Home/CVE/Traefik is an HTTP reverse proxy and load balancer. Versions 3.5.0 through 3.6.2 have inverted TLS verification logic in
CVE

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

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.

MEDIUM · CVSS 5.9 EPSS 9e-05
Monitor
  • No active-exploitation, high-EPSS, or public-exploit signals - routine patching cadence
Sigma rules0 YARA rules0
⬡

Weakness Classification

CWE-295Improper Certificate Validation
▤

Affected Products & Versions

1
traefik>= 3.5.0 and < 3.6.3
▤

Affected Packages

3
Language-ecosystem packages (from OSV) tied to this CVE, with the version that fixes it - the dependency-level detail NVD doesn’t carry.
Go github.com/traefik/traefik
Go github.com/traefik/traefik/v2
Go github.com/traefik/traefik/v3 MODERATE fixed in 3.6.3
▣

Scoring & Timeline

5.9
MEDIUM · CVSS v3.1 · security-advisories@github.com
View on NVD
Attack Vector
Network Adjacent Local Physical
Attack Complexity
Low High
Privileges Required
None Low High
User Interaction
None Required
Scope
Unchanged Changed
Confidentiality
None Low High
Integrity
None Low High
Availability
None Low High
Published to NVD09 Dec 2025 · 01:16 AM
CVSS VectorCVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:N/A:N
SSVC triage · cisa-vulnrichment
Exploitation
none
Automatable
no
Technical impact
partial
SSVC asks the questions that actually drive patch urgency: is it being exploited, can attacks be automated, and how total is the impact.
⚑

Vendor Advisories

1
suse-csafopenSUSE-SU-2026:10020-1
🔗

References & Sources

3
Source URLs (vendor pages, mailing lists, write-ups). Exploit/PoC links are in their own section above to avoid duplication.
https://github.com/traefik/traefik/commit/14a1aedf5704673d875d210d7bacf103a43c77e4Patch
https://github.com/traefik/traefik/releases/tag/v3.6.3Release Notes
https://github.com/traefik/traefik/security/advisories/GHSA-7vww-mvcr-x6vjPatchVendor Advisory
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