CVE-2026-121966 (CVSS 8.7)

Description

Traefik 2.x before 2.11.60 and 3.x before 3.7.16 sends ForwardAuth subrequests (and, in 3.7, Ingress NGINX auth-url requests) through an auth-server connection pool shared by all clients, exposing connection-bound NTLM or Negotiate authentication. An unauthenticated attacker can reuse another user's authenticated connection, receiving the victim's identity via authResponseHeaders to access backends as that user.

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CVSS v3.1 Score

8.7

HIGH

CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:H/I:H/A:N

EPSS — Exploit Prediction

0.0033

Probability of exploitation

0.27%

Percentile rank

EPSS estimates the probability that this vulnerability will be exploited in the wild within the next 30 days. A higher score means more likely to be exploited.

Weakness Type (CWE)

CWE-488 CWE-488

References

Other References

https://github.com/traefik/traefik/security/advisories/GHSA-hrpp-p4fc-wwf8 https://www.vulncheck.com/advisories/traefik-before-2.11.60-and-3.7.16-forwardauth-ntlm-negotiate-identity-leak

Frequently Asked Questions

What is CVE-2026-121966? +

Traefik 2.x before 2.11.60 and 3.x before 3.7.16 sends ForwardAuth subrequests (and, in 3.7, Ingress NGINX auth-url requests) through an auth-server connection pool shared by all clients, exposing connection-bound NTLM or Negotiate authentication. An unauthenticated attacker can reuse another user's authenticated connection, receiving the victim's identity via authResponseHeaders to access backends as that user. It has a CVSS v3.1 base score of 8.7 (HIGH).

How severe is CVE-2026-121966? +

CVE-2026-121966 has a CVSS v3.1 score of 8.7 out of 10, rated HIGH. This is a high-severity vulnerability that should be prioritized for patching. The EPSS score is 0.0033, placing it in the 0th percentile for exploitation probability.

How do I check if I'm vulnerable to CVE-2026-121966? +

You can use Secably's free Website Scanner to check your website for known vulnerabilities. For infrastructure scanning, use the Port Scanner to identify exposed services that may be affected. Check the vendor advisories linked above for specific patch and version information.

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