High [CVE-2026-71325] Namespace isolation bypass via TraefikService backendRef

Traefik is an open-source edge router that makes publishing services a fun and easy experience. Prior to 2.11.54, 3.6.25, and 3.7.10, cross-namespace @kubernetescrd references are not rejected for TraefikService backend references resolved by the service resolver.

A tenant confined by RBAC to a single namespace can therefore bind its own router to a TraefikService owned by another namespace and expose or reroute that namespace's backend, defeating the namespace isolation allowCrossNamespace=false is meant to enforce. This issue is fixed in version 2.11.54, 3.6.25, 3.7.10.

A flaw was found in Traefik. This flaw allows a tenant, even when restricted by Role-Based Access Control (RBAC) to a single namespace, to bypass namespace isolation.

This defeats the intended `allowCrossNamespace=false` enforcement, leading to unauthorized access or manipulation of services across namespaces. A flaw in Traefik's service resolver allows a lower-privileged tenant to reference and bind cross-namespace TraefikService objects via @kubernetescrd, even when allowCrossNamespace=false is configured.

By creating a custom router targeting an isolated TraefikService CRD in a separate namespace, an authenticated attacker can bypass namespace isolation controls, intercepting or rerouting backend service traffic across multi-tenant boundaries.