CVE-2026-88008: Traefik

Critical severity, CVSS 9.1. EPSS: 0.5% chance of exploitation in the next 30 days.

Traefik is an open source HTTP reverse proxy and load balancer. From 2.11.26 until 2.11.57 and 3.7.13, Traefik forwards a client-supplied Connection header requesting Upgrade, the Upgrade: h2c token, and HTTP2-Settings to a shared backend. If the backend accepts h2c and returns 101 Switching Protocols, Traefik enters a raw tunnel and no longer applies routers, BasicAuth, ForwardAuth, IPAllowList, RateLimit, access logging, metrics, or tracing to later HTTP/2 requests, allowing an unauthenticated request through an unprotected route to reach protected paths on the same backend. This issue is fixed in 2.11.57 and 3.7.13.

Affected products

• Traefik Traefik: from 2.11.26, before 2.11.57 (fixed in 2.11.57); from 3.4.2, before 3.7.13 (fixed in 3.7.13)

Published 2026-09-10. Last modified 2026-09-14.