CVE-2026-125109
Rack: Rack::Request#host_with_port (and #base_url / #url) return the raw invalid Host header — incomplete fix of CVE-2026-34835
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.
Fixes and workarounds
No remediation reported in collected sources.
Missing remediation information is not evidence that no patch exists.
Affected products and versions
| Product | Versions | Authority |
|---|---|---|
| rack rack |
>= 3.0, < 3.1.23 (affected) >= 3.2, < 3.2.8 (affected) |
CNA: GitHub_M |
Version ranges are source assertions. Check the vendor advisory and your installed configuration before determining exposure.
CVSS assessments
| Version / score | Vector | Authority |
|---|---|---|
| 3.1 / 4.8 medium |
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:N | CNA: GitHub_M |
Exploit evidence
No exploit evidence in collected sources. This is not proof of no exploitation.
References
- https://github.com/rack/rack/security/advisories/GHSA-2j8w-xcrc-x985CNA: GitHub_M · x_refsource_CONFIRM
- https://github.com/rack/rack/commit/4380381a56dc52556a436d6d794c8e18dc8b0565CNA: GitHub_M · x_refsource_MISC
- https://github.com/rack/rack/commit/49386f460286b7346c7003b69a839de782cc8a39CNA: GitHub_M · x_refsource_MISC
- https://github.com/rack/rack/releases/tag/v3.1.23CNA: GitHub_M · x_refsource_MISC
- https://github.com/rack/rack/releases/tag/v3.2.8CNA: GitHub_M · x_refsource_MISC
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