CVE-2026-54763
Traefik is an HTTP reverse proxy and load balancer. Prior to v2.11.51, v3.6.22, and v3.7.6, Traefik's BasicAuth, DigestAuth, and ForwardAuth middlewares strip canonical-cased spoofed identity headers before writing Traefik's own value, but do not account for underscore-variant header names, which many backends normalize identically to dashed forms. An attacker able to reach a protected route can inject an underscore-variant header that survives Traefik's stripping and reaches the backend alongside, or on the unauthenticated ForwardAuth authResponseHeaders path instead of, the value Traefik intended to set, spoofing identity or authorization context. This issue is fixed in versions v2.11.51, v3.6.22, and v3.7.6.
No public exploitation has been reported so far. A fixed version is available (see the table below).
Recommended action: Update to the fixed version listed for your distribution using the native package manager.
Severity metrics
CVSS 4.0 : 7.8 HIGH · CVSS 3.1 : 10.0 CRITICAL
Vector: AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:N/SC:H/SI:H/SA:N
Affected & fixed versions by distribution
Versions are the native distribution strings (backport-aware): RHEL/Debian/SUSE backport fixes, so compare with the distro version comparator (dpkg / rpm / vercmp), not the upstream version.
| Distribution | Package | Affected | Fixed version | Status |
|---|---|---|---|---|
| openSUSE:Tumbleweed | traefik | - | 3.7.7-1.1 | fixed |