CVE-2025-66491: Traefik

Medium severity, CVSS 5.9. EPSS: 0.2% chance of exploitation in the next 30 days.

Traefik is an HTTP reverse proxy and load balancer. Versions 3.5.0 through 3.6.2 have inverted TLS verification logic in 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. This issue is fixed in version 3.6.3.

Affected products

• Traefik Traefik: from 3.5.0, before 3.6.3 (fixed in 3.6.3)

Published 2025-12-09. Last modified 2026-06-17.