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CVE-2026-125109

MEDIUMCVSS 4.8/10EPSS 0.22%

Last modified

CVE-2026-125109 is a medium-severity vulnerability rated 4.8/10 on the CVSS scale. 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. EPSS estimates a 0.22% chance of exploitation in the next 30 days.

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.

Metrics

CVSS 3.1
4.8/10

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

EPSS Probability
0.22%

12.9th percentile

Probability of exploitation in the next 30 days. Learn more

Weakness Enumeration

Affected Software

Source: CNA advisory (CVE.org). NVD analysis pending.

VendorProductVersions
rackrack>= 3.0, < 3.1.23; >= 3.2, < 3.2.8

References

Timeline

Published
Last Modified
Status
Received

Frequently Asked Questions

What is 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.
How severe is CVE-2026-125109?
CVE-2026-125109 has a CVSS score of 4.8/10 (MEDIUM severity). The EPSS model estimates a 0.22% probability of exploitation in the next 30 days.
How do I fix CVE-2026-125109?
Check the vendor references and advisories linked above for patched versions and mitigation guidance. You can also run a Strix scan to test if your systems are affected.

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Source: NVD / NIST