CVE-2026-88007: Traefik HTTP/3 Backend NTLM Connection Reuse

Severity: critical (CVSS 9.1 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.6% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2026-09-10 · updated 2026-09-14
Weakness: CWE-287

Description

Traefik is an open source HTTP reverse proxy and load balancer. From 2.11.0 until 2.11.57 and 3.7.13, the HTTP/3 entrypoint ConnContext does not call service.AddTransportOnContext, so kerberosRoundTripper uses a shared backend transport instead of a transport dedicated to each frontend connection. With HTTP/3 enabled, a backend using connection-bound NTLM or Negotiate authentication, and backend keep-alive, an unrelated client can reuse a backend connection authenticated for a victim, read victim-only data, and act as that victim without the victim credentials. This issue is fixed in 2.11.57 and 3.7.13.

Affected products

Traefik: from 2.8.2 before 2.11.56; from 3.0.0 before 3.7.12 — fixed in 2.11.56, 3.7.12

How to fix

Upgrade to a fixed version: Traefik 2.11.56, 3.7.12. Check the vendor advisory for mitigations.

References

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