Traefik Inverted TLS Verification Logic in ingress-nginx Provider

Exploitation

No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.

CVSS

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

EPSS

• CVE-2025-66491: 0.22% estimated exploitation activity in the next 30 days; percentile 12.72 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.

As published by the source; long descriptions are shortened.

Impact There is a potential vulnerability in Traefik NGINX provider managing the nginx.ingress.kubernetes.io/proxy-ssl-verify annotation. The provider inverts the semantics of 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. Patches - https://github.com/traefik/traefik/releases/tag/v3.6.3 For more information If you have any questions or comments about this advisory, please open an issue. <details <summaryOriginal Description</summary Summary A logic error in Traefik's experimental ingress-nginx provider inverts the semantics of 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…

Published by the source

8 Dec 2025, 16:43 UTC

Last modified by the source

9 Dec 2025, 16:32 UTC

Source last checked

26 Oct 2026, 15:13 UTC

1. Revision 1 · created · 26 Oct 2026

   Published from ghsa record GHSA-7vww-mvcr-x6vj

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# Patch Next advisory brief: CVE-2025-66491

Advisory: Traefik Inverted TLS Verification Logic in ingress-nginx Provider
IDs: CVE-2025-66491, GHSA-7vww-mvcr-x6vj
Record: https://patchnext.com/advisories/cve-2025-66491 (revision 1, source checked 26 Oct 2026, 15:13 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: Medium (CVSS 5.9)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: github.com/traefik/traefik/v3 3.6.3. A vendor fix does not mean a deployment is fixed.

## Affected components
- Go github.com/traefik/traefik/v3: affected >= 3.5.0, <= 3.6.2; fixed in 3.6.3

## Suggested inspection (read-only)
- Go github.com/traefik/traefik/v3: check the installed version with your package manager.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on github.com/traefik/traefik/v3.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://github.com/advisories/GHSA-7vww-mvcr-x6vj (GitHub-reviewed advisory GHSA-7vww-mvcr-x6vj lists affected ranges: Go github.com/traefik/traefik/v3 >=3.5.0 <=3.6.2)

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