CVE-2025-66491
Medium
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.
SeverityMedium
CVSS5.9
Exploit probability—
Product
Traefik
PublishedDec 9, 2025
First seenDec 9, 2025
Weakness typeCWE-295CWE-295
How to fix
Update
- traefik traefik3.6.3 or later
- github.com/traefik/traefik/v33.6.3 or later
Affected products
| Product | Affected versions | Fixed in |
|---|---|---|
| traefik traefik | 3.5.0 ≤ v < 3.6.3 | 3.6.3 |
| github.com/traefik/traefik/v3Go | 3.5.0 ≤ v < 3.6.3 | 3.6.3 |
| github.com/traefik/traefikGo | No range specified | — |
| github.com/traefik/traefik/v2Go | No range specified | — |
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