Traefik: HTTP/3 mTLS bypass via exact SNI TLSOptions lookup for wildcard and mixed-case hosts

Summary

Traefik is an HTTP reverse proxy and load balancer. Versions prior to 3.7.3, 3.6.18, and 2.11.51 have a critical vulnerability in Traefik's HTTP/3 (QUIC) TLS configuration selection that allows unauthenticated clients to bypass router-specific mTLS enforcement. When HTTP/3 is enabled on an entrypoint, the TLS handshake selects the applicable TLS configuration through an exact, case-sensitive lookup on the SNI value, which fails to match wildcard host patterns (e.g., *.example.com) or case variants of the configured hostname. Because the handshake falls back to the default TLS configuration — which may not require client certificates — a client can complete the QUIC handshake without presenting a certificate, while the subsequent HTTP routing layer still dispatches the request to a backend protected by a router-specific mTLS policy. The issue affects deployments where HTTP/3 is enabled, a router uses a wildcard Host rule or case-insensitive hostname matching, a router-specific TLSOptions enforces client certificate authentication, and UDP access to the entrypoint is reachable by an attacker. This vulnerability is fixed in versions 3.7.3, 3.6.18, and 2.11.51.

Timeline

1. Jun 23, 2026, 7:13 PM UTCCVE published
2. Jun 25, 2026, 12:44 PM UTCCISA SSVC assessment

   Exploitation: none · Automatable: yes · Technical impact: partial

3. Sep 2, 2026, 12:04 PM UTCRecord last updated

Affected versions

• traefik traefik

  From 3.7.0 · fixed in 3.7.3; From 3.0.0 · fixed in 3.6.18; fixed in 2.11.51

• github.com/traefik/traefik/v3Go

  From 3.7.0 · fixed in 3.7.3

• github.com/traefik/traefik/v2Go

  fixed in 2.11.51

• github.com/traefik/traefikGo

  through 1.7.34

• github.com/traefik/traefik/v3Go

  fixed in 3.6.18

• github.com/traefik/traefikGo

  All versions

• github.com/traefik/traefik/v3Go

  fixed in 3.7.3

References 8