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
CVSS Score
4.8
EPSS Score
0.0%
EPSS Percentile
0th
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.
| CWE | CWE-1286 |
| Vendor | rack |
| Product | rack |
| Published | Nov 9, 2026 |
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CVSS v3 Breakdown
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:N Attack Vector
Network
Attack Complexity
High
Privileges Required
None
User Interaction
None
Scope
Unchanged
Confidentiality
Low
Integrity
Low
Availability
None
Affected Versions
rack / rack
>= 3.0, < 3.1.23 >= 3.2, < 3.2.8
References
github.com: https://github.com/rack/rack/security/advisories/GHSA-2j8w-xcrc-x985 github.com: https://github.com/rack/rack/commit/4380381a56dc52556a436d6d794c8e18dc8b0565 github.com: https://github.com/rack/rack/commit/49386f460286b7346c7003b69a839de782cc8a39 github.com: https://github.com/rack/rack/releases/tag/v3.1.23 github.com: https://github.com/rack/rack/releases/tag/v3.2.8