CVE-2026-39858

A flaw was found in Traefik. A remote attacker can exploit an authentication bypass vulnerability by injecting spoofed trust context through unsanitized alias headers. This is due to Traefik's forwarded-header sanitization logic not properly handling alias header names that use underscores instea...

GHSA-5M6W-WVH7-57VM Traefik: Pre-authentication decision bypass due to forwarded alias spoofing

Summary There is a high severity authentication bypass vulnerability in Traefik's ForwardAuth and snippet-based authentication middleware. Traefik's forwarded-header sanitization logic targets only canonical header names e.g., X-Forwarded-Proto and does not strip or normalize alias variants that...