CVE-2026-54761: Traefik: Kubernetes Gateway crossProviderNamespaces bypass allows HTTPRoute outside the allowlist to expose internal Traefik services

There is a high severity vulnerability in Traefik’s Kubernetes Gateway provider affecting the crossProviderNamespaces allowlist. For HTTPRoute rules that declare multiple (WRR) backendRefs, Traefik evaluates the allowlist against the target backendRef.namespace instead of the route’s own namespace. As a result, an HTTPRoute created in a namespace that is not allow-listed can reference a cross-provider TraefikService such as api@internal, dashboard@internal or rest@internal by pointing backendRef.namespace at an allow-listed namespace covered by a Gateway API ReferenceGrant, exposing internal Traefik services on the data plane. Exploitation requires the ability to create an accepted HTTPRoute and a matching ReferenceGrant from an allow-listed namespace ; it does not require any change to Traefik static configuration, RBAC, or the deployment itself.

The Kubernetes Gateway provider’s crossProviderNamespaces option is documented as restricting which Gateway API route namespaces may declare TraefikService backendRefs.

For HTTPRoute rules with multiple backendRefs, Traefik checks this allowlist against backendRef.namespace instead of the HTTPRoute namespace. A route in a namespace that is not allow-listed can therefore add api@internal to the generated WRR service by setting backendRef.namespace to an allow-listed namespace, as long as a normal Gateway API ReferenceGrant permits that cross-namespace reference.

Verified affected versions:

• v3.7.1 (fa49e2bcad7ffd8a80accdf1fae1ae480913d93d)
• current source/master tested by me (29406d42898547f1ffabd904f66af06c212740cf)