Rack: Rack::Request#host_with_port (and #base_url / #url) return the raw invalid Host header — incomplete fix of CVE-2026-34835

MITRE NVD CVE.ORG JSON API

Summary

CVECVE-2026-125109
StatePUBLISHED
AssignerGitHub_M
Source PriorityCVE Program / NVD first with legacy fallback
Published2026-11-09 22:18:42 UTC
Updated2026-11-10 17:17:26 UTC
DescriptionRack 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.

Risk And Classification

Primary CVSS: v3.1 4.8 MEDIUM from [email protected]

CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:N

Problem Types: CWE-1286 | CWE-1286 CWE-1286: Improper Validation of Syntactic Correctness of Input

VersionSourceTypeScoreSeverityVector
3.1[email protected]Secondary4.8MEDIUMCVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:N
3.1CNADECLARED4.8MEDIUMCVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:N

CVSS v3.1 Breakdown

Attack Vector
Network
Attack Complexity
High
Privileges Required
None
User Interaction
None
Scope
Unchanged
Confidentiality
Low
Integrity
Low
Availability
None

CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:N

Vendor Declared Affected Products

SourceVendorProductVersionPlatforms
CNA Rack Rack affected >= 3.0, < 3.1.23 Not specified
CNA Rack Rack affected >= 3.2, < 3.2.8 Not specified

References

ReferenceSourceLinkTags
github.com/rack/rack/commit/4380381a56dc52556a436d6d794c8e18dc8b0565 [email protected] github.com
github.com/rack/rack/security/advisories/GHSA-2j8w-xcrc-x985 [email protected] github.com
github.com/rack/rack/releases/tag/v3.1.23 [email protected] github.com
github.com/rack/rack/commit/49386f460286b7346c7003b69a839de782cc8a39 [email protected] github.com
github.com/rack/rack/releases/tag/v3.2.8 [email protected] github.com
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