Traefik: `allowCrossNamespace=false` bypass via `@kubernetescrd` TraefikService backendRef

Summary There is a medium severity vulnerability in Traefik's Kubernetes CRD provider. When providers.kubernetesCRD.allowCrossNamespace is disabled — the default — cross-namespace @kubernetescrd references are rejected for middlewares, TLS options and HTTP/TCP ServersTransports, but the same...