Medium severity · published Dec 9, 2025
CVE-2025-66491
Traefik has Inverted TLS Verification Logic in its ingress-nginx Provider
5.9
CVSS
0.2%
EPSS
No
On KEV
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:N
Attack vector
Network
Complexity
High
Privileges
None
User interaction
None
Confidentiality
High
Integrity
None
Availability
None
Scope
Unchanged
Exploitation
Is it being used?
Exploit prediction (EPSS)0.2% · higher than 13% of CVEs
Exploited in the wildNo evidence yet
CISA KEVNot listed
Ransomware campaign useNot known
Affected products
Which versions
TR
traefik · traefik
>= 3.5.0, < 3.6.3 · source: vendor, NVD
References
NVD
https://nvd.nist.gov/vuln/detail/CVE-2025-66491
CVE.org
https://www.cve.org/CVERecord?id=CVE-2025-66491
Patch
https://github.com/traefik/traefik/commit/14a1aedf5704673d875d210d7bacf103a43c77e4
Release Notes
https://github.com/traefik/traefik/releases/tag/v3.6.3
Patch
https://github.com/traefik/traefik/security/advisories/GHSA-7vww-mvcr-x6vj
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