CVE-2026-85596 in Traefik
Summary
by MITRE • 09/04/2026
Traefik versions >= v3.7.0 and <= v3.7.10 contain an authentication bypass in the Kubernetes Ingress NGINX provider. The TLS option generated for an Ingress carrying the nginx.ingress.kubernetes.io/auth-tls-secret annotation was named after the Ingress namespace and name. As a result, two Ingress objects sharing the same host, the same client CA secret, and the same client-authentication mode produced two distinct TLS option names for that host. Traefik treats this as a TLS options conflict and falls back to the entry point's default TLS configuration, which does not request a client certificate, so a route configured with nginx.ingress.kubernetes.io/auth-tls-verify-client: "on" becomes reachable without a client certificate. Only the v3.7 line is affected; the issue is fixed in v3.7.11.
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Analysis
by VulDB Data Team • 09/04/2026
Traefik versions ranging from 3.7.0 to 3.7.10 contain a critical authentication bypass vulnerability within its Kubernetes Ingress NGINX provider, specifically affecting how TLS options are generated for ingress resources that utilize client certificate verification. The root cause of this flaw lies in the naming convention used for internal TLS configuration objects. When Traefik processes an Ingress object annotated with nginx.ingress.kubernetes.io/auth-tls-secret to enforce mutual Transport Layer Security (mTLS), it generates a unique identifier for the associated TLS option based on the ingress namespace and name rather than solely on the host or certificate parameters. This design decision creates a scenario where two distinct Ingress objects, which share identical hosts, client Certificate Authority secrets, and authentication modes, result in separate and conflicting TLS option names within Traefik's internal configuration store.
The operational impact of this conflict is severe because Traefik interprets the presence of multiple TLS options for the same host as a configuration error or ambiguity. In response to this perceived conflict, the software falls back to the default TLS configuration defined at the entry point level rather than applying the specific mTLS settings intended by the administrator. The default entry point configuration typically does not request or verify client certificates. Consequently, any route configured with the annotation nginx.ingress.kubernetes.io/auth-tls-verify-client set to on becomes accessible without requiring a valid client certificate from the connecting party. This effectively nullifies the authentication mechanism that was explicitly intended for those services, allowing unauthorized access to protected endpoints.
From a security classification perspective, this vulnerability represents an Authentication Bypass via Configuration Error, aligning with CWE-287 in the Common Weakness Enumeration framework. The flaw allows attackers to bypass protective mechanisms by exploiting how configuration conflicts are resolved within the application logic. In terms of adversary behavior, this could facilitate unauthorized access to sensitive backend services that rely on client certificates for identity verification, potentially leading to data exfiltration or further lateral movement if those services handle privileged operations. This aligns with techniques observed in MITRE ATT&CK where attackers exploit misconfigurations to bypass authentication controls.
To mitigate this vulnerability, organizations running Traefik versions 3.7.0 through 3.7.10 must upgrade immediately to version 3.7.11 or later, which resolves the naming conflict and ensures that TLS options are correctly applied even when multiple ingress resources target the same host with identical authentication requirements. Until an upgrade is performed, administrators should review their Kubernetes Ingress configurations for duplicate hosts using client certificate verification and consider implementing network-level access controls as a temporary compensating measure to restrict traffic to those specific services until the software patch can be deployed.