CVE-2026-54763

Critical · CVSS 10.0

Traefik — HTTP header spoofing via underscore-variant header bypass in authentication middleware (BasicAuth, DigestAuth, ForwardAuth)

CVSS: 10.0; nvd
EPSS: —
KEV: No
Class: oss containerizable; CWE-178, CWE-290, CWE-345

Description

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.

Search profile — drives PoC discovery

Symbols BasicAuthDigestAuthForwardAuthauthResponseHeadersX-Forwarded-Usercanonical-casedunderscore-variantheader strippingGHSA-x677-9fxg-v5c5108a5264473a2cbc8f12d6d691a3c6553cdf2c1b

Keywords CVE-2026-54763Traefik header spoofingTraefik underscore header bypassTraefik BasicAuth bypassTraefik ForwardAuth spoofTraefik DigestAuth bypassGHSA-x677-9fxg-v5c5Traefik identity header injectionTraefik auth middleware bypassTraefik CWE-178 CWE-290 CWE-345

Versions: < v2.11.51, < v3.6.22, < v3.7.6

References

Status: enriched · ingested 2026-07-09T00:00:39.000Z · profiled 2026-07-09T00:30:39.000Z