GHSA-X677-9FXG-V5C5 Traefik: Incomplete fix for CVE-2026-33433 + CVE-2026-39858 cross-cohort: headerField underscore-variant identity spoofing in BasicAuth / DigestAuth / ForwardAuth

Summary There is a high severity vulnerability in Traefik's BasicAuth, DigestAuth, and ForwardAuth middlewares. The fix for CVE-2026-33433 stripped canonical-cased spoofed identity headers e.g. X-Auth-User before writing Traefik's own value, but did not account for underscore-variant header names...

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...

Puma's header normalization allows for client to clobber proxy set headers

Impact Clients could clobber values set by intermediate proxies such as X-Forwarded-For by providing a underscore version of the same header X-ForwardedFor. Any users trusting headers set by their proxy may be affected. Attackers may be able to downgrade connections to HTTP non-SSL or redirect...

CVE-2024-45614 Header normalization allows for client to clobber proxy set headers in Puma

Puma is a Ruby/Rack web server built for parallelism. In affected versions clients could clobber values set by intermediate proxies such as X-Forwarded-For by providing a underscore version of the same header X-ForwardedFor. Any users relying on proxy set variables is affected. v6.4.3/v5.6.9 now...