Traefik before 2.11.60 and 3.7.16 ForwardAuth NTLM/Negotiate Identity Leak
Only Traefik 2.x before 2.11.60 and 3.x before 3.7.16 using a ForwardAuth middleware whose authentication server uses NTLM or SPNEGO/Kerberos Negotiate are covered. Fixed in 2.11.60 and 3.7.16.
Written by anthropic/claude-haiku-5.5 from the sources below. Verify against them.
- Exploited
- No known exploitation
- Fix
- Fixed in 2.11.60, 3.7.16
- Who is exposed
- Not reported
Do first: Upgrade to a fixed version: 2.11.60, 3.7.16.
- Exploitation0/40No signal
- Exposure17/25No login or user action needed, reachable over the network without a login · Data gap: Advisories don't say whether default setups are affected
- Reach?/20Reach: unknown (data gap). No tracked technology or package matched
- Severity8/10CVSS 7.0, total technical impact per CISA
- No patch0/5No signal
What would change the score
- Would score about 70 if added to CISA KEV
- Would score about 65 if CISA's SSVC rates exploitation active
- Would score about 30 if advisories confirm default setups are exposed
CVE-2026-121966 is not in CISA's Known Exploited Vulnerabilities (KEV) catalog. No public exploit code is tracked. It is rated CVSS 7.0 (high) and affects traefik; fixed in 2.11.60 and 3.7.16.
- Last modified
- Where the record stands: published, rejected by its publisher, or superseded by another id.What do these mean? →
- Published
- Whether CISA lists it in its Known Exploited Vulnerabilities catalog: proof that attackers are using it.What do these mean? →
- Not listed in CISA KEV
- A 0-100 score for how much a CVE matters across the industry: exploitation, exposure, how widely the software is used, severity and whether a fix exists.What do these mean? →
- 25/100 · provisional
- How many real-world setups can hit the bug, from the vendor's advisory and CISA data. It does not know your setup.What do these mean? →
- Unclear
- Fix
- Fixed in 2.11.60, 3.7.16
- Whether working attack code is public (Exploit-DB, Metasploit, Nuclei or GitHub). Public code makes attacks easier.What do these mean? →
- None on Exploit-DB, Metasploit or GitHub
- Exploitation: none
- Automatable: no
- Technical impact: total
Summary
Traefik 2.x and 3.x (before the patched releases) can let an unauthenticated attacker over the network reuse another user's authenticated NTLM or Negotiate connection through the shared ForwardAuth auth-server pool. Successful reuse gives the attacker that user's identity, letting them reach backend services as the victim, and this requires a non-default setup only if noted elsewhere, which the facts here do not establish.
Read the original 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.
What to do
Upgrade to a fixed version: 2.11.60, 3.7.16.
Timeline
- CVE published
- First seen by cve.now
- CISA SSVC assessment
Exploitation: none · Automatable: no · Technical impact: total
- Record last updated
Affected versions
- traefik traefik
fixed in 2.11.60
- traefik traefik
From 3.0.0 · fixed in 3.7.16
Evidence 2
- Advisory
- Link
Corrections
None so far.
Something wrong on this page? Report an error. Every fix is listed here.
Questions about CVE-2026-121966
Is CVE-2026-121966 being exploited?
It is not in CISA's Known Exploited Vulnerabilities catalog, and CISA's SSVC assessment does not mark exploitation as active. That does not mean it has not been attacked: vendors and researchers can report attacks before CISA lists them. No public exploit code is tracked.Source: cve.now feed data
What does this mean?
ForwardAuth checks each request with an external authentication server. When that server uses a connection-bound scheme such as NTLM or SPNEGO/Kerberos Negotiate, an unauthenticated client can receive a successful authentication response that carries another user's identity, letting it access backends as that user.Source: github.com, vulncheck.com
Which versions are affected by CVE-2026-121966?
traefik: before 2.11.60. traefik: from 3.0.0 before 3.7.16.Source: cve.now feed data
Am I affected, and how do I check?
Traefik 2.x before 2.11.60 and 3.x before 3.7.16 are in scope, with the setup being a ForwardAuth middleware whose authentication server uses NTLM or Negotiate. In Traefik 3.7, Ingress NGINX auth-url external authentication requests are also in scope. To check, run the traefik version command and review the forwardAuth middleware configuration to see which authentication scheme its server uses.Source: github.com, vulncheck.com
How do I fix CVE-2026-121966?
Upgrade to Traefik 2.11.60 or 3.7.16, depending on the release line in use. No workaround is listed in the facts.Source: github.com, vulncheck.com