CVE-2025-66491

Name: CVE-2025-66491
Creator: NVD / NIST
Published: 2025-12-09T01:16:55.72+00:00
License: https://creativecommons.org/publicdomain/zero/1.0/

MEDIUMCVSS 5.9/10EPSS 0.21%

Last modified Jun 17, 2026

CVE-2025-66491 is a medium-severity vulnerability rated 5.9/10 on the CVSS scale. 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. EPSS estimates a 0.21% chance of exploitation in the next 30 days.

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.

Metrics

CVSS 3.1

5.9/10

CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:N/A:N

EPSS Probability

0.21%

10.6th percentile

Probability of exploitation in the next 30 days. Learn more

Weakness Enumeration

CWE-295

Affected Software

Vendor	Product	Versions
Traefik	Traefik	>= 3.5.0, < 3.6.3

References

https://github.com/traefik/traefik/commit/14a1aedf5704673d875d210d7bacf103a43c77e4Patch
https://github.com/traefik/traefik/releases/tag/v3.6.3Release Notes
https://github.com/traefik/traefik/security/advisories/GHSA-7vww-mvcr-x6vjPatch, Vendor Advisory

Timeline

Published: Dec 9, 2025
Last Modified: Jun 17, 2026
Status: Analyzed

Frequently Asked Questions

What is CVE-2025-66491?

How severe is CVE-2025-66491?

CVE-2025-66491 has a CVSS score of 5.9/10 (MEDIUM severity). The EPSS model estimates a 0.21% probability of exploitation in the next 30 days.

How do I fix CVE-2025-66491?

Check the vendor references and advisories linked above for patched versions and mitigation guidance. You can also run a Strix scan to test if your systems are affected.

Are you affected by CVE-2025-66491?

Run a free Strix scan to check your systems for this vulnerability.

Scan your code now

Source: NVD / NIST