Vulnerability in Rack
CVE-2026-125109
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.
Published .
CVSS v3 metric
CVSS v3 base score 4.8 (Medium). Vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:N.
EPSS exploit prediction
No EPSS score from FIRST.org yet. New CVEs usually get one within a few days; no score means no signal yet, not low risk. How EPSS works.
Affected products
- Rack — versions >= 3.0, < 3.1.23, >= 3.2, < 3.2.8
Weakness classification (CWE)
References
- https://github.com/rack/rack/security/advisories/GHSA-2j8w-xcrc-x985
- 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
Frequently asked questions
- What is CVE-2026-125109?
- CVE-2026-125109 is a medium-severity vulnerability in Rack, classified under CWE-1286. CVSS score: 4.8/10. Published 2026-11-09.
- How severe is CVE-2026-125109?
- Medium severity. CVSS v3 base score is 4.8 out of 10.