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Fencer Vulns
medium 5.9

CVE-2025-66491 json

Traefik has Inverted TLS Verification Logic in its ingress-nginx Provider

published 2025-12-08 11 mo ago modified 2026-10-14 25 d ago also EUVD-2025-201730 , GHSA-7vww-mvcr-x6vj , GO-2025-4205

cvss
5.9
version 3.1, CNA
cisa kev
Not listed
not in CISA's catalog
epss
0.2%
EPSS 0.2% chance of exploitation in 30 days, percentile 12%
public exploits
0
none known

Summary

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.

Patch / fix

  • go github.com/traefik/traefik/v3 3.6.3
  • traefik traefik 3.6.3
  • govulncheck-vulndb openSUSE Leap 15.6 0.0.20251230T014957-150000.1.134.1

suse advisories SUSE-SU-2026:0037-1

  • govulncheck-vulndb openSUSE Leap 16.0 0.0.20260723T184607-160000.1.1
  • traefik openSUSE Tumbleweed 3.6.6-1.1

opensuse advisories openSUSE-SU-2026:21483-1openSUSE-SU-2026:10020-1

Vendor advisories

What the vendors themselves say about their products: affected, fixed or not affected, and what to do.

red hat product security vex CVE-2025-66491 updated cvss 5.9

github.com/traefik/traefik: Traefik has Inverted TLS Verification Logic in its ingress-nginx Provider

  • Red Hat OpenShift Dev Spaces devspaces/traefik-rhel9
    affected: workaround, no fix available “Fix deferred”

Red Hat CSAF VEX © Red Hat, Inc., from https://security.access.redhat.com/data/csaf/v2/vex/; changed: reduced to product statuses and remediations. CC BY 4.0 · csaf

CISA SSVC

Exploitation
none
Automatable
no
Technical impact
partial
Assessed
11 mo ago

Exploit prediction

0.22% chance of exploitation in the next 30 days, higher than 12% of all scored CVEs (FIRST EPSS, 2026-11-08).

CVSS scores

assigned by version score vector
CNA 3.1 5.9 CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:N/A:N
GitHub 3.1 5.9 CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:N/A:N

Affected packages

ecosystem package affected fixed in
go github.com/traefik/traefik/v3
>=3.5.0, <3.6.3
3.6.3
go github.com/traefik/traefik
all versions
 no fix listed
go github.com/traefik/traefik/v2
all versions
 no fix listed

Affected products

  • traefik traefik

Classification

Weakness
  • CWE-295 Improper Certificate Validation

References

Sources

Fencer Vulns keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.

CPEs and fixed versions use Anchore's correction of NVD's data: Added CPE configurations because not yet analyzed by NVD.