Authentication Bypass Affecting traefik-fips-3 package, versions <3.7.12-r0
Threat Intelligence
The probability is the direct output of the EPSS model, and conveys an overall sense of the threat of exploitation in the wild. The percentile measures the EPSS probability relative to all known EPSS scores. Note: This data is updated daily, relying on the latest available EPSS model version. Check out the EPSS documentation for more details.
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Test your applications- Snyk IDSNYK-MINIMOSLATEST-TRAEFIKFIPS3-19829752
- published16 Sept 2026
- disclosed10 Sept 2026
Introduced: 10 Sep 2026
CVE-2026-88879 (opens in a new tab)How to fix?
Upgrade Minimos:latest traefik-fips-3 to version 3.7.12-r0 or higher.
NVD Description
Note: Versions mentioned in the description apply only to the upstream traefik-fips-3 package and not the traefik-fips-3 package as distributed by Minimos.
See How to fix? for Minimos:latest relevant fixed versions and status.
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.
References
- https://www.cve.org/CVERecord?id=CVE-2026-88879
- https://github.com/advisories/GHSA-cwr6-3wm2-9xhw
- https://osv.dev/vulnerability/MINI-v23m-c3ph-2j7p
- https://osv.dev/vulnerability/CVE-2026-88879
- 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