What’s Vulnerable › Vulnerabilities

CVE-2026-88011: Traefik: ForwardAuth identity spoofing via dot-form header alias

• Severity: high (CVSS 8.1 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 0.4% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2026-09-10 · updated 2026-09-15
• Weakness: CWE-290

Description

Traefik is an open source HTTP reverse proxy and load balancer. Prior to 2.11.56, and from 3.0.0 until 3.7.12, a client-supplied dot-form header such as X.Authenticated.User survives ForwardAuth replacement and underscoreHeadersStrategy because Go treats it as distinct from X-Authenticated-User while normalization-prone CGI, WSGI, PHP, and NGINX backends collapse both names. A backend can consequently consume the client value instead of the identity Traefik asserted, allowing identity spoofing for any header managed by Traefik. The aliasHeadersStrategy protection is disabled by default and must be configured as delete or reject. The mitigation is available in 2.11.56 and 3.7.12.

Affected products

• Traefik: before 2.11.56; from 3.0.0 before 3.7.12 — fixed in 2.11.56, 3.7.12

How to fix

Upgrade to a fixed version: Traefik 2.11.56, 3.7.12. Check the vendor advisory for mitigations.

References

• https://github.com/traefik/traefik/commit/0331801c72329e0eaeb850e53ccce87c57fbecf8
• https://github.com/traefik/traefik/pull/13720
• https://github.com/traefik/traefik/releases/tag/v2.11.56
• https://github.com/traefik/traefik/releases/tag/v3.7.12
• https://github.com/traefik/traefik/security/advisories/GHSA-rf44-j88r-hh8c

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