CVE-2025-66491

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 v3.1 Score

5.9

MEDIUM

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

Weakness Type (CWE)

CWE-295 CWE-295

Affected Products

Vendor	Product	Versions
traefik	traefik	3.5.0 — 3.6.3

References

Advisories & Patches

https://github.com/traefik/traefik/commit/14a1aedf5704673d875d210d7bacf103a43c77e4 https://github.com/traefik/traefik/security/advisories/GHSA-7vww-mvcr-x6vj

Other References

https://github.com/traefik/traefik/releases/tag/v3.6.3

Frequently Asked Questions

What is 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. It has a CVSS v3.1 base score of 5.9 (MEDIUM).

How severe is CVE-2025-66491? +

CVE-2025-66491 has a CVSS v3.1 score of 5.9 out of 10, rated MEDIUM. This is a medium-severity vulnerability that should be remediated as part of regular maintenance.

What products are affected by CVE-2025-66491? +

CVE-2025-66491 affects products from traefik, specifically: traefik. Check the affected products table above for specific version ranges.

How do I check if I'm vulnerable to CVE-2025-66491? +

You can use Secably's free Website Scanner to check your website for known vulnerabilities. For infrastructure scanning, use the Port Scanner to identify exposed services that may be affected. Check the vendor advisories linked above for specific patch and version information.

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