CVE-2026-54765: Traefik: Gateway HTTPRoute backendRef filters can leak backend context across routes sharing a Service:port

There is a medium severity vulnerability in Traefik’s Kubernetes Gateway API provider. When two accepted HTTPRoutes target the same backend Service:port but configure different backendRef filters, Traefik may resolve both routes to the same child service and apply only one route’s filter set to all requests reaching that backend. In Gateway deployments where backendRef filters set security-sensitive headers — such as tenant identity, authorization context, or values the backend trusts — an attacker who can create an accepted HTTPRoute sharing the same backend Service:port may cause their route’s filter context to be applied to another route’s requests, potentially crossing namespace boundaries when a ReferenceGrant permits cross-namespace targeting.

Traefik’s Kubernetes Gateway API provider builds the dynamic HTTP backend service key for a Gateway HTTPRoute backendRef from only the backend namespace, Service name, protocol, and port. It does not include the HTTPRoute, listener, rule, or backendRef filter identity in that key.

When two accepted HTTPRoutes point to the same backend Service:port but define different backendRef filters, Traefik can make both route WRR services reference the same child service. The child service then carries only one backendRef filter set, so one route can send requests to the backend with another route’s backend context.

This is security-relevant when backendRef filters set, remove, or rewrite security-sensitive context, such as tenant, identity, auth, sanitization, Host, or path headers trusted by the backend.

Credit: Qican Ma, Ding Luo @XiaoMi ShadowBlade Security Lab