CVE-2026-48491

There is a high severity vulnerability in Traefik's domain-fronting protection (`SNICheck`) that allows an unauthenticated client to bypass mutual TLS enforced through wildcard router `TLSOptions`. When a router uses a wildcard host rule such as `Host(`*.example.com`)` with stricter TLS options (for example `RequireAndVerifyClientCert`), `SNICheck` resolves the TLS options for the HTTP `Host` header using exact map lookups only and never applies wildcard matching. If another permissive SNI is served on the same entrypoint, an attacker can complete the TLS handshake under the permissive options and then send an HTTP `Host` header targeting the wildcard-protected backend, reaching it without presenting a client certificate. This affects the regular HTTPS / HTTP-2 path and does not require HTTP/3. Traefik's `SNICheck` domain-fronting protection ignores wildcard `TLSOptions` mappings. A wildcard router such as `Host("*.example.com")` can require mTLS for direct access, but an unauthenticated client can complete the TLS handshake with another permissive SNI on the same entrypoint and then send `Host: api.example.com` / HTTP request authority `api.example.com` to reach the wildcard-protected backend. This issue does not require HTTP/3. The PoC uses the regular HTTPS/HTTP2 path and abuses the domain-fronting consistency check between TLS SNI and the HTTP `Host` header. For HTTP/2, this corresponds to the request authority / `Host` value as exposed to Traefik's HTTP request handling.

EPSS 0.36% · 29.2th percentile