Description
Traefik is an HTTP reverse proxy and load balancer. Prior to versions 2.11.42, 3.6.11, and 3.7.0-ea.3, when `headerField` is configured with a non-canonical HTTP header name (e.g., `x-auth-user` instead of `X-Auth-User`), an authenticated attacker can inject their own canonical version of that header to impersonate any identity to the backend. The backend receives two header entries — the attacker-injected canonical one is read first, overriding Traefik's non-canonical write. Versions 2.11.42, 3.6.11, and 3.7.0-ea.3 patch the issue.
Affected products
Version statuses are supplied by the assigning organization. Consult the original record for detailed ranges and platform conditions.
traefik traefik
< 2.11.42affected>= 3.0.0-beta1, < 3.6.11affected>= 3.7.0-ea.1, < 3.7.0-ea.3affected
References
- https://github.com/traefik/traefik/security/advisories/GHSA-qr99-7898-vr7c ↗
- https://github.com/traefik/traefik/releases/tag/v2.11.42 ↗
- https://github.com/traefik/traefik/releases/tag/v3.6.11 ↗
- https://github.com/traefik/traefik/releases/tag/v3.7.0-ea.3 ↗
- https://access.redhat.com/security/cve/CVE-2026-33433 ↗
- https://bugzilla.redhat.com/show_bug.cgi?id=2452289 ↗
- https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-33433.json ↗
- https://access.redhat.com/errata/RHSA-2026:10175 ↗