{"id":"EUVD-2026-75429","revision":"915fed59264d401fb0ed767463357aa3","records":[{"revision":"915fed59264d401fb0ed767463357aa3","observedAt":"2026-10-28T10:35:40.501+00:00","statement":{"source":"euvd","id":"EUVD-2026-75429","aliases":["CVE-2026-88879","GHSA-cwr6-3wm2-9xhw"],"title":"Traefik is an HTTP reverse proxy and load balancer. In Traefik v1.x, v2.x through v2.11.55, and v3.0.0 through v3.7.11, header names are canonicalized only on dashes, so X-Auth-User, X_Auth_User and X.Auth.User are treated as three distinct…","description":"Traefik is an HTTP reverse proxy and load balancer. In Traefik v1.x, v2.x through v2.11.55, and v3.0.0 through v3.7.11, header names are canonicalized only on dashes, so X-Auth-User, X_Auth_User and X.Auth.User are treated as three distinct headers by Traefik, while backends that derive variable names from header names (CGI, WSGI, PHP, NGINX and others) collapse them into a single variable. A client can therefore smuggle a dot-form alias of a header that Traefik manages past the middleware managing it — for example supplying X.Authenticated.User alongside the canonical X-Authenticated-User written by the ForwardAuth middleware — causing such a backend to read the client-supplied value instead of the identity Traefik asserted. In the tested configuration (PHP 8.2 built-in SAPI over an HTTP/1 backend path), Go's lexical header ordering makes the attacker-supplied value win deterministically, so a client that ForwardAuth admits as a low-privilege identity can be treated by the backend as a different user or role. Any header Traefik sets is affected, not only ForwardAuth's. This is an incomplete fix for GHSA-x677-9fxg-v5c5, which blocked only the underscore form. Fixed in v2.11.56 and v3.7.12, which add the aliasHeadersStrategy entry-point option; because it defaults to 'keep' for backwards compatibility, it must be explicitly set to 'delete' or 'reject' for the fix to take effect. Unmaintained release lines will not receive a patch.","state":0,"publishedAt":null,"modifiedAt":null,"affected":[],"metrics":[{"system":"EUVD CVSS 4.0","vector":"CVSS:4.0/AV:N/AC:L/AT:P/PR:L/UI:N/VC:N/VI:N/VA:N/SC:H/SI:H/SA:N","score":5.3,"severity":null}],"references":["https://github.com/traefik/traefik/security/advisories/GHSA-rf44-j88r-hh8c","https://www.vulncheck.com/advisories/traefik-before-2.11.56-identity-spoofing-via-header-alias"],"sourceUrl":"https://euvd.enisa.europa.eu/vulnerability/EUVD-2026-75429","license":"ENISA EUVD · source terms and attribution apply","enrichment":{"sourceStatus":null,"weaknesses":[],"productCriteria":[],"sourceDates":{"datePublished":"Sep 10, 2026, 1:05:30 PM","dateUpdated":"Oct 8, 2026, 3:25:59 PM"},"relatedAdvisories":[],"note":"EUVD source date text has no stated timezone and is retained without inventing a UTC instant. Related bulletin membership is not an alias, common cause or applicability claim. A missing vector with a zero score is treated as unrated. Complete vendor/product and underlying source evidence remains in the original JSON."},"key":"euvd:EUVD-2026-75429","identifiers":["EUVD-2026-75429","CVE-2026-88879","GHSA-cwr6-3wm2-9xhw"]},"retained":false,"historicalAffected":[]}],"coverage":[]}