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Fencer Intel
medium 4.8

CVE-2026-125109 json

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

published 2d ago modified yesterday also EUVD-2026-120482 , GHSA-2j8w-xcrc-x985

cvss
4.8
version 3.1, CNA
cisa kev
Not listed
not in CISA's catalog
epss
0.2%
EPSS 0.2% chance of exploitation in 30 days, percentile 12%
public exploits
0
none known

Summary

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.

Patch / fix

  • rubygems rack 3.1.23, 3.2.8
  • ruby-rack Debian 14 3.2.8-1

debian advisories DEBIAN-CVE-2026-125109

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Vendor advisories

What the vendors themselves say about their products: affected, fixed or not affected, and what to do.

red hat product security vex CVE-2026-125109 updated cvss 4.8

rack: Rack: Security bypass and URL manipulation via invalid HTTP host headers

  • Red Hat 3scale API Management Platform 2 3scale-amp2/backend-rhel8
    affected: workaround, no fix available “Fix deferred”
  • Red Hat 3scale API Management Platform 2 3scale-amp2/zync-rhel9, 3scale-amp2/system-rhel8, 3scale-amp2/system-rhel9 Red Hat Enterprise Linux 7 pcs, pcs-snmp, python-clufter, pcs 0.12.3-3.el10 Red Hat Enterprise Linux 8 pcs, pcs-snmp, pcs 0.12.3-3.el10 Red Hat Enterprise Linux 9 pcs, pcs-snmp, pcs 0.12.3-3.el10 Red Hat Enterprise Linux 10 pcs 0.12.3-3.el10 Red Hat OpenStack Platform 13 (Queens) rhosp13/openstack-redis, rhosp13/openstack-haproxy, rhosp13/openstack-mariadb, rhosp13/openstack-rabbitmq, rhosp13/openstack-ovn-northd, rhosp13/openstack-manila-share, +2 more
    +2 more products
    Red Hat OpenStack Platform 16.2 rhosp-rhel8/openstack-redis, rhosp-rhel8/openstack-haproxy, rhosp-rhel8/openstack-mariadb, rhosp-rhel8/openstack-rabbitmq, rhosp-rhel8/openstack-ovn-northd, rhosp-rhel8/openstack-manila-share, +2 more Red Hat OpenStack Platform 17.1 rhosp-rhel9/openstack-redis, rhosp-rhel9/openstack-haproxy, rhosp-rhel9/openstack-mariadb, rhosp-rhel9/openstack-rabbitmq, rhosp-rhel9/openstack-ovn-northd, rhosp-rhel9/openstack-manila-share, +2 more
    not affected: vulnerable code not present

Red Hat CSAF VEX © Red Hat, Inc., from https://security.access.redhat.com/data/csaf/v2/vex/; changed: reduced to product statuses and remediations. CC BY 4.0 · csaf

CISA SSVC

Exploitation
none
Automatable
no
Technical impact
partial
Assessed
yesterday

Exploit prediction

0.22% chance of exploitation in the next 30 days, higher than 12% of all scored CVEs (FIRST EPSS, 2026-11-11).

CVSS scores

assigned by version score vector
CNA 3.1 4.8 CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:N
GitHub 3.1 4.8 CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:N

Affected packages

ecosystem package affected fixed in
rubygems rack
>=3.0.0, <3.1.23
>=3.2.0, <3.2.8
3.1.23
3.2.8

Affected products

  • rack rack

Classification

Weakness
  • CWE-1286 Improper Validation of Syntactic Correctness of Input

References

Sources

Fencer Intel keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.