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CVE-2026-85596 – Authentication Bypass (mTLS) – Traefik v3.7.0 through v3.7.10

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Summary

CVE-2026-85596 is an authentication bypass in Traefik’s Kubernetes Ingress NGINX provider that lets an attacker reach routes protected by mutual TLS (mTLS) client-certificate authentication without presenting a valid client certificate. The issue affects the Traefik v3.7 release line and carries a CVSS v4.0 base score of 8.2 (High).

Technical details

  • Root cause: Traefik names the generated TLS option for an Ingress carrying the nginx.ingress.kubernetes.io/auth-tls-secret annotation after the Ingress’s namespace and name, rather than after the host/client-CA/auth-mode combination.
  • Trigger condition: Two or more Ingress objects share the same host, the same client CA secret, and the same client-authentication mode, but have different Ingress names — producing two distinct TLS option identifiers for that single host.
  • Effect of the conflict: Traefik detects this as a TLS options conflict and falls back to the entry point’s default TLS configuration, which does not request a client certificate.
  • Attack vector: Network-based, no privileges or user interaction required; an attacker simply connects to the affected host without a client certificate.
  • Impact: A route configured with nginx.ingress.kubernetes.io/auth-tls-verify-client: "on" becomes reachable without mTLS enforcement, exposing confidentiality of the protected backend (no integrity or availability impact per the CVSS vector).

Affected software

  • Traefik versions >= v3.7.0 and <= v3.7.10 (per the official advisory description)
  • CVE record version ranges list affected versions through v3.7.12, with the fix landing in v3.7.11
  • Only the v3.7 release line is affected; v2.11 and v3.6 lines are not impacted by this CVE

Severity

  • CVSS v4.0 Base Score: 8.2 (High)
  • Vector: CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:H/VI:N/VA:N/SC:N/SI:N/SA:N

Mitigation and recommended actions

  • Immediate: Upgrade to Traefik v3.7.11 or later, where the TLS option naming has been fixed.
  • If patching is not immediately possible: Audit Kubernetes Ingress objects for any that share the same host and the same auth-tls-secret/auth-tls-verify-client configuration but have different Ingress names, and consolidate them into a single Ingress object (or ensure only one Ingress defines the TLS/mTLS policy per host) to avoid triggering the conflicting-TLS-option fallback.
  • Review access/authentication logs for connections reaching mTLS-protected routes without a client certificate as a compromise indicator.

How IONIX identifies potentially affected assets

IONIX matches the following signals against data already collected when it crawled the asset; identifying the technology sends no request beyond that crawl.

  • Page title: Traefik or Traefik Proxy
  • Content-Security-Policy response header: frame-src 'self' https://traefik.io https://*.traefik.io;

References

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