CVE-2026-33433: Traefik

High severity, CVSS 8.8. EPSS: 0.6% chance of exploitation in the next 30 days.

Traefik is an HTTP reverse proxy and load balancer. Prior to versions 2.11.42, 3.6.11, and 3.7.0-ea.3, when `headerField` is configured with a non-canonical HTTP header name (e.g., `x-auth-user` instead of `X-Auth-User`), an authenticated attacker can inject their own canonical version of that header to impersonate any identity to the backend. The backend receives two header entries — the attacker-injected canonical one is read first, overriding Traefik's non-canonical write. Versions 2.11.42, 3.6.11, and 3.7.0-ea.3 patch the issue.

Affected products

• Traefik Traefik: before 2.11.42 (fixed in 2.11.42); from 3.0.0, before 3.6.12 (fixed in 3.6.12); version 3.7.0 only

Published 2026-03-27. Last modified 2026-07-15.