CVE-2025-66491 — Improper Certificate Validation in Traefik Traefik V3

CWE-295 — Improper Certificate Validation6 documents5 sources
Severity
5.9MEDIUMNVD
EPSS
0.0%
top 98.89%
CISA KEV
Not in KEV
Exploit
No known exploits
Affected products
2
Github.com Traefik Traefik V3Traefik
Timeline
PublishedDec 9
Latest updateDec 15

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 vector

CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:N/A:NExploitability: 2.2 | Impact: 3.6

Affected Packages3 packages

▶NVDtraefik/traefik3.5.0 — 3.6.3
▶Gogithub.com/traefik_traefik_v33.5.0 — 3.6.3
▶CVEListV5traefik/traefik>= 3.5.0, < 3.6.3

Patches

Patch: github.com ↗Patch: github.com ↗

🔴Vulnerability Details

4
OSV
Traefik Inverted TLS Verification Logic in ingress-nginx Provider in github.com/traefik/traefik↗2025-12-15
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CVEList
Traefik has Inverted TLS Verification Logic in its ingress-nginx Provider↗2025-12-09
▶
OSV
Traefik Inverted TLS Verification Logic in ingress-nginx Provider↗2025-12-08
▶
GHSA
Traefik Inverted TLS Verification Logic in ingress-nginx Provider↗2025-12-08
▶

📋Vendor Advisories

1
Red Hat
github.com/traefik/traefik: Traefik has Inverted TLS Verification Logic in its ingress-nginx Provider↗2025-12-09
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CVE-2025-66491 — Improper Certificate Validation | cvebase