CVE-2025-66491: Traefik Inverted TLS Verification Logic in ingress-nginx Provider

December 8, 2025 (updated December 9, 2025)

A logic error in Traefik’s experimental ingress-nginx provider inverts the semantics of the nginx.ingress.kubernetes.io/proxy-ssl-verify annotation. Setting the annotation to "on" (intending to enable backend TLS certificate verification) actually disables verification, allowing man-in-the-middle attacks against HTTPS backends when operators believe they are protected.

References

github.com/advisories/GHSA-7vww-mvcr-x6vj
github.com/traefik/traefik
github.com/traefik/traefik/commit/14a1aedf5704673d875d210d7bacf103a43c77e4
github.com/traefik/traefik/releases/tag/v3.6.3
github.com/traefik/traefik/security/advisories/GHSA-7vww-mvcr-x6vj
nvd.nist.gov/vuln/detail/CVE-2025-66491

Code Behaviors & Features

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