CVE-2026-85596

Traefik before v2.11.55 contains a TLS option conflict resolution vulnerability that allows unauthenticated attackers to bypass client-certificate authentication by creating conflicting TLS options on multi-host routers. Attackers can reach protected backends by exploiting shared TLS resolution across multiple hostnames in a single router rule, causing the strict mTLS requirement to fall back to default options for all hosts.

Traefik versions from v3.7.1 fail to enforce crossProviderNamespaces restrictions on the traefik.ingress.kubernetes.io/service.middlewares Service annotation in the Kubernetes Ingress provider. A namespace-limited tenant excluded from the allowlist can attach an operator-owned middleware to its Service, and if that middleware injects backend credentials, recover them at a controlled backend.

Traefik versions before v2.11.55 contain an authentication bypass vulnerability in the digestAuth middleware where unknown usernames receive an empty secret instead of rejection. Attackers can compute a valid digest response using the empty secret to bypass authentication on any digestAuth-protected route.

In Traefik prior to versions v2.11.51, v3.6.22, and v3.7.6, the BasicAuth, DigestAuth, and ForwardAuth middlewares fail to strip underscore-variant identity headers that backends normalize to dashed forms. An attacker can inject such a header to spoof identity or bypass authorization.

Traefik versions prior to 3.7.3, 3.6.18, and 2.11.51 have a critical vulnerability in HTTP/3 (QUIC) TLS configuration selection that allows unauthenticated clients to bypass router-specific mTLS enforcement. When HTTP/3 is enabled, the TLS handshake selects the TLS configuration via exact, case-sensitive SNI lookup, failing to match wildcard host patterns or case variants. This allows clients to complete the QUIC handshake without presenting a certificate, while the HTTP routing layer still dispatches requests to protected backends.

In Traefik versions 3.7.0 through 3.7.3, a vulnerability in the domain-fronting protection (SNICheck) allows an unauthenticated client to bypass mutual TLS enforced by wildcard router rules. The attacker can complete a TLS handshake under permissive options for a different SNI and then send an HTTP request with a Host header targeting the wildcard-protected backend without presenting a client certificate.

In Traefik prior to versions 2.11.48, 3.6.19, and 3.7.3, a high severity vulnerability exists in the StripPrefix middleware. An unauthenticated attacker can bypass route-level authentication and authorization by using paths containing .. or %2e%2e, which after normalization resolve to protected resources.

A vulnerability in Traefik allows a user with HTTPRoute creation permissions in the Kubernetes Gateway API provider to bypass the providers.rest.insecure=false setting and access the REST provider handler. By accepting TraefikService backends with names ending in @internal, traffic can be routed to rest@internal, enabling unauthorized reconfiguration of routers and services in shared Gateway deployments.

A high severity authentication bypass vulnerability was found in Traefik's ForwardAuth and snippet-based authentication middleware. The issue stems from improper sanitization of header aliases using underscores instead of dashes, allowing an attacker to inject spoofed trust context and bypass authentication without valid credentials.

An authentication bypass vulnerability was found in Traefik's ForwardAuth middleware when trustForwardHeader=false is set and Traefik runs behind a trusted upstream proxy. The issue is fixed in versions 2.11.43, 3.6.14, and 3.7.0-rc.2.