CVE-2026-54763: Traefik: headerField underscore-variant identity spoofing in BasicAuth / DigestAuth / ForwardAuth

Severity: critical (CVSS 10.0 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.2% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2026-07-06 · updated 2026-07-08
Weakness: CWE-178

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.

Affected products

Traefik: before 2.11.51; from 3.0.0 before 3.6.22; from 3.7.0 before 3.7.6 — fixed in 2.11.51, 3.6.22, 3.7.6

How to fix

Upgrade to a fixed version: Traefik 2.11.51, 3.6.22, 3.7.6. Check the vendor advisory for mitigations.

References

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