Vulnerability in Traefik
CVE-2025-66491
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.
Vulnerability class: Improper Certificate Validation
Published · last modified .
CVSS v3 metric
CVSS v3 base score 5.9 (Medium). Vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:N/A:N.
EPSS exploit prediction
EPSS: 0.002 (11.4th percentile), scored .
Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 11th percentile — 11.4% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.
EPSS over last 30 days · oldest: 0.002 · newest: 0.002 · change: -0.000
Affected products
- Traefik — versions >= 3.5.0, < 3.6.3
Weakness classification (CWE)
References
- github.com/traefik/traefik/security/advisories/GHSA-7vww-mvcr-x6vj (Patch, Vendor Advisory)
- github.com/traefik/traefik/commit/14a1aedf5704673d875d210d7bacf103a43c77e4 (Patch)
- github.com/traefik/traefik/releases/tag/v3.6.3 (Release Notes)
Frequently asked questions
- What is CVE-2025-66491?
- CVE-2025-66491 is a medium-severity vulnerability in Traefik, classified under Improper Certificate Validation. CVSS score: 5.9/10. Published 2025-12-09.
- How severe is CVE-2025-66491?
- Medium severity. CVSS v3 base score is 5.9 out of 10.