CVE-2026-125109

Description

Rack is a modular Ruby web server interface. From 3.0 until 3.1.23 and 3.2.8, Rack::Request#host_with_port, #base_url, and #url can return an attacker-controlled invalid authority from Host, X-Forwarded-Host, or Forwarded: host= verbatim. Applications without an independent host allowlist that use these methods for absolute URLs, redirects, or origin-dependent checks can emit attacker-chosen delimiters, enabling redirect manipulation, string-based allowlist bypass, or unescaped markup reflection. Rails overrides these methods and is not expected to be affected. This issue is fixed in versions 3.1.23 and 3.2.8.

References

• https://github.com/rack/rack/commit/4380381a56dc52556a436d6d794c8e18dc8b0565
• https://github.com/rack/rack/commit/49386f460286b7346c7003b69a839de782cc8a39
• https://github.com/rack/rack/releases/tag/v3.1.23
• https://github.com/rack/rack/releases/tag/v3.2.8
• https://github.com/rack/rack/security/advisories/GHSA-2j8w-xcrc-x985