CVE-2025-66491 | Traefik has Inverted TLS Verification Logic in its ingress-nginx Provider

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.

Published: 2025-12-09 Last update: 2026-01-02 Assigner: [email protected] Source: [email protected]
NVD Status：Analyzed，CVE State: published
View at NVD, CVE.org, EUVD

CVE-2025-66491 is rated Low Risk (23.7/100): CVSS Medium severity, with low exploitation likelihood (EPSS 0.01%). Monitor for updates and reassess as exploit intelligence or EPSS changes.

Risk is dynamic; we continuously reassess and refresh what is shown on this page as upstream context changes.

Exploit prediction scoring system (EPSS) score for CVE-2025-66491

EPSS lead: Daily EPSS estimates relative likelihood of exploitation; percentile ranks this CVE among scored vulnerabilities (higher = more severe relative rank).

# Date Old EPSS score New EPSS score Delta (New - Old)
1 2025-12-09 — 0.01% —

Full EPSS history (1 record total)

Common vulnerability scoring system (CVSS) metrics for CVE-2025-66491

CVSS metrics for this CVE.

Base score Version Severity Vector Exploitability Impact Score source
5.9 3.1 MEDIUM
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:N/A:N Click to expand
Attack vector (AV:N)
Could be attacked over the internet or any normal routed network—not just someone sitting at the machine.
Attack complexity (AC:H)
Even with access, the exploit needs extra luck, timing, or a fussy environment to actually work.
Privileges required (PR:N)
No account or special rights needed—anonymous or random user is enough.
User interaction (UI:N)
Nobody has to click “OK” or open a trap file; it can work without a victim helping.
Scope (S:U)
Damage stays in the same “trust bubble” as the broken component—no big spill into unrelated systems.
Confidentiality (C:H)
Serious risk that confidential data gets exposed in a big way.
Integrity (I:N)
Data isn’t meaningfully altered or forged.
Availability (A:N)
Service keeps running; no real outage angle.
 2.2 3.6 [email protected]

Weakness enumeration for CVE-2025-66491

GitHub Security Advisory for CVE-2025-66491

GHSA-7vww-mvcr-x6vj · Severity: medium · Ecosystem: go — Traefik Inverted TLS Verification Logic in ingress-nginx Provider

OS Trackers for CVE-2025-66491

vendor priority summary link
alpine — CVE-2025-66491: 1 source package rows (traefik); 10 state rows across 2 repos (3.23-community, edge-community); fixed 0, open 10. https://security.alpinelinux.org/vuln/CVE-2025-66491
redhat medium — https://access.redhat.com/security/cve/CVE-2025-66491

Affected software / configurations for CVE-2025-66491

Vendor Product Version Raw CPE
traefik traefik >= 3.5.0, < 3.6.3 cpe:2.3:a:traefik:traefik:*:*:*:*:*:*:*:*

References for CVE-2025-66491

cvelogic Threat Intelligence