VulnerabilityAnalyzed

CVE-2025-66491

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.

MEDIUM 5.9EPSS 0.22%

Does this matter?

Lower severity and a low EPSS score (0.22%). Track it; it rarely justifies an emergency change on its own.

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.

CVSS 3.1: 5.9 MEDIUMCVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:N/A:N
EPSS: 0.22% probability · 13th percentile
CISA KEV: Not listed
Weakness: CWE-295
Affected: traefik/traefik
Source: security-advisories@github.com

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

Source: NVD record, EPSS from FIRST.org, KEV from CISA. Refreshed daily.