Traefik: IngressRouteTCP ignores crossProviderNamespaces, letting any namespace borrow file-provider mTLS identity

Impact

Traefik enforced the crossProviderNamespaces allowlist only for HTTP serversTransport references, not for the TCP equivalent. A tenant who can create an IngressRouteTCP in any namespace can point its service at serversTransport: foo@file and make the shared ingress use a file-provider TCPServersTransport that was meant for a different, trusted namespace - including the privileged backend mTLS client certificate, the SPIFFE identity, or PROXY-protocol settings defined in the static config. On a multi-tenant GPU cluster where one Traefik instance fronts tenant inference and notebook endpoints, that is a tenant borrowing the cluster's trusted client identity to reach backends it should not be able to authenticate to. Confidentiality and integrity of the subsequent (cross-)system are the rated impact; Traefik itself is not crashed or read out.

Who can reach it

Any authenticated Kubernetes user with permission to create or edit an IngressRouteTCP in a namespace that is not in crossProviderNamespaces - i.e. a normal tenant namespace, no cluster-admin needed.

What to do

Upgrade Traefik to 3.6.23 or 3.7.7 and restart the ingress controller pods; a rolling restart of the Traefik deployment is enough and no node maintenance is required. Until then, audit existing IngressRouteTCP objects for serversTransport references carrying an @file provider suffix, and restrict who may create IngressRouteTCP via RBAC or admission policy.

References

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