Critical [CVE-2026-48020] Authentication bypass in StripPrefix middleware allows unauthorized access to protected paths

Traefik is an HTTP reverse proxy and load balancer. Prior to 2.11.48, 3.6.19, and 3.7.3, there is a high severity vulnerability in Traefik's StripPrefix middleware that allows an unauthenticated attacker to bypass route-level authentication and authorization.

When a public router matches on a PathPrefix rule and applies the StripPrefix middleware, a request path containing.. or its percent-encoded form %2e%2e can match the public route at routing time and then, after the prefix is stripped and the path is normalized, resolve to a path served by a separate, authenticated router.

As a result, an attacker can reach protected backend paths — such as admin or internal configuration endpoints — without satisfying the authentication middleware attached to the protected router. This vulnerability is fixed in 2.11.48, 3.6.19, and 3.7.3.

By crafting a request path containing '..' or its percent-encoded form, an attacker can access protected backend paths, such as administrative or internal configuration endpoints, without proper authentication. This could lead to unauthorized information disclosure or modification of sensitive settings.

This is an Important authentication bypass flaw in Traefik's StripPrefix middleware, affecting Red Hat OpenShift Dev Spaces. Red Hat severity: Important — CVSS 9.1 (CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N).

Weakness: CWE-22.