CVE-2026-85594

Traefik v3.7.1 and later fail to enforce crossProviderNamespaces allowlist restrictions when processing the traefik.ingress.kubernetes.io/service.middlewares annotation on Services in the Kubernetes Ingress provider. In a multi-tenant cluster, a tenant whose namespace is excluded from the allowlist can still attach an operator-owned middleware defined in another namespace to its own Service. If that middleware injects backend credentials (for example auth headers or tokens), the tenant can recover those credentials at a backend it controls, potentially exposing credentials that grant access to other resources in the cluster. Only Traefik v3.7.1+ deployments using the Kubernetes Ingress provider in multi-tenant configurations with cross-namespace middleware allowlists are affected. No public proof-of-concept, in-the-wild exploitation, or KEV listing is known, and EPSS assigns a low ~0.2% probability of exploitation within 30 days.

What to do: Upgrade Traefik to a release that enforces crossProviderNamespaces for the service.middlewares annotation (check the vendor advisory for the patched version, as none is specified here). In the meantime, audit tenant Services for the traefik.ingress.kubernetes.io/service.middlewares annotation referencing middlewares outside the tenant's namespace, and rotate any credentials injected by operator-owned middlewares that tenants could have captured via their own backends.