CVE-2025-66491

MEDIUM

Traefik 3.5.0-3.6.2 - Improper Certificate Validation via proxy-ssl-verify Annotation

Title source: llm
STIX 2.1

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.

References (3)

Core 3

Scores

CVSS v3 5.9
EPSS 0.0021
EPSS Percentile 10.5%
Attack Vector NETWORK
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:N/A:N

CISA SSVC

Vulnrichment
Exploitation none
Automatable no
Technical Impact partial

Details

CWE
CWE-295
Status published
Products (2)
traefik/traefik 3.5.0 - 3.6.3
traefik/traefik 3.5.0 - 3.6.3Go
Published Dec 09, 2025
Tracked Since Feb 18, 2026