Traefik CVE-2026-85594

Exploitation requires all of the following concurrent conditions to be met: (1) Traefik v3.7.1 or later is deployed as the Kubernetes Ingress controller with crossProviderNamespaces configured to restrict cross-namespace middleware references for at least one tenant namespace; (2) the attacker holds a Kubernetes identity with write access to Service resources within their assigned namespace - a standard tenant role, not cluster-admin; (3) an operator-managed middleware exists in a namespace outside the tenant's allowlist that injects authentication credentials - such as an Authorization header, API key, or BasicAuth header - into backend requests toward protected systems; and (4) the attacker can deploy or observe a backend endpoint that receives and records HTTP request headers. Deployments where tenant RBAC prevents Service annotation modification, where no credential-injecting middlewares are in use, or where all namespaces are already within the crossProviderNamespaces allowlist are not practically exploitable.

The CVSS 4.0 score of 7.0 reflects a moderate-to-high real-world priority in affected multi-tenant environments, anchored by AT:P (specific attack preconditions must hold), which prevents broad automated exploitation. The high confidentiality impact on both the vulnerable system (VC:H) and subsequent systems (SC:H) reflects that stolen middleware-injected credentials may grant access to backend infrastructure well beyond the Traefik instance itself. CISA KEV status is absent and no public exploit code has been confirmed, suggesting mass exploitation has not yet occurred. EPSS data is not available in the provided intelligence, so exploitation probability must be inferred from the CVSS precondition metrics alone. The practical risk is meaningful for organizations running shared Traefik ingress controllers with credential-injecting operator middlewares; even a mid-sized municipal IT team in mielec operating Traefik as a shared ingress layer for departmental tenants should treat this as urgent if any operator middlewares inject API keys or bearer tokens into backend requests. Environments without credential-injecting middlewares, or with strict admission controls preventing tenants from modifying Service annotations, face significantly reduced practical risk despite the high confidentiality impact rating.

An attacker with a standard tenant Kubernetes account in a restricted namespace annotates a Service resource with traefik.ingress.kubernetes.io/service.middlewares referencing an operator middleware in a namespace they are not allowed to access. Traefik v3.7.1+ skips the crossProviderNamespaces validation for this annotation path and attaches the middleware - which adds an Authorization bearer-token header to every backend request - to the attacker's ingress traffic, forwarding requests to an attacker-controlled HTTP endpoint that logs all incoming headers, yielding the operator's long-lived credential. No public exploit code exists at time of analysis, and the attack requires only standard Kubernetes tooling such as kubectl.