Vulnerability · Published Jul 6, 2026 · Assigned by GitHub_M

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

High 7.8

In plain English

A high-severity authentication bypass by spoofing in traefik from traefik. There are no confirmed reports of exploitation so far. The chance it is exploited in the next 30 days is estimated at 0.2% (higher than 15% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.

Severity (CVSS 4.0)7.8High

Exploit odds (30 days)0.2%top 84.9% of all CVEs

Exploited in the wildNo reportsCISA SSVC: none

Attack toolingNoneno public tooling known

Official 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 packages & fixed versions

Ecosystem	Package	Fixed in	Advisory
Go	github.com/traefik/traefik	no fix listed	GO-2026-6211
Go	github.com/traefik/traefik/v2	2.11.51	GHSA-x677-9fxg-v5c5
Go	github.com/traefik/traefik/v2	2.11.51	GO-2026-6211
Go	github.com/traefik/traefik/v3	3.6.22	GHSA-x677-9fxg-v5c5
Go	github.com/traefik/traefik/v3	3.7.6	GHSA-x677-9fxg-v5c5
Go	github.com/traefik/traefik/v3	3.6.22, 3.7.6	GO-2026-6211

Affected products (as reported)

Vendor	Product	Versions
traefik	traefik	< 2.11.51>= 3.0.0-beta1, < 3.6.22>= 3.7.0-ea.1, < 3.7.6

Weakness: CWE-178, CWE-290, CWE-345 · Vector: CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:N/SC:H/SI:H/SA:N

References

https://github.com/traefik/traefik/security/advisories/GHSA-x677-9fxg-v5c5 x_refsource_CONFIRM
https://github.com/traefik/traefik/pull/13262 x_refsource_MISC
https://github.com/traefik/traefik/commit/108a5264473a2cbc8f12d6d691a3c6553cdf2c1b x_refsource_MISC