CVE-2025-66491 Traefik has Inverted TLS Verification Logic in its ingress-nginx Provider
Traefik's ingress-nginx provider incorrectly disables TLS verification when enabled, allowing man-in-the-middle attacks against HTTPS backends.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2025-66491?
CVE-2025-66491 is a medium-severity vulnerability in Traefik Traefik, published on 9 Dec 2025. An attacker can exploit it over the internet without logging in, with no action from the victim.
Official description
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.
Weakness: CWE-295
Which versions are affected by CVE-2025-66491?
5 open source packages ship an affected version, including github.com/traefik/traefik/v3, github.com/traefik/traefik and github.com/traefik/traefik/v2. It affects 1 product.
| Package | Affected | Fixed in |
|---|---|---|
github.com/traefik/traefik/v3 Go | From 3.5.0 | 3.6.3 |
github.com/traefik/traefik/v3 Go | From 3.5.0 | 3.6.3 |
github.com/traefik/traefik/v3 Go | From 3.5.0 | 3.6.3 |
github.com/traefik/traefik Go | All versions | None |
github.com/traefik/traefik/v2 Go | All versions | None |
Products include Traefik Traefik.
How do I fix CVE-2025-66491?
Upgrade github.com/traefik/traefik/v3 to 3.6.3 or later.
Is CVE-2025-66491 being exploited?
There is no known exploitation of CVE-2025-66491 in the wild and no public exploit code.
Other vulnerabilities in Traefik Traefik
- CVE-2024-45410 HTTP client can remove the X-Forwarded headers in Traefik
- CVE-2026-88877 Traefik v3.7.0 Authentication Bypass via from-to-www-redirect
- CVE-2026-85595 Traefik before v2.11.55 and v3.0.0 through v3.7.10 Authentication Bypass via digestAuth
- CVE-2026-88007 Traefik HTTP/3 Backend NTLM Connection Reuse
- CVE-2026-88009 Traefik: Rootless HTTP/1 request-target routes as "/" but is forwarded verbatim, bypassing path-scoped routing, middleware guards and access logging
Sources
Also known as GHSA-7vww-mvcr-x6vj, GO-2025-4205, MINI-2gpr-f46c-76fm, MINI-34hh-5w9m-w3j8.