GHSA-vrch-868g-9jx5 Traefik allows path traversal using url encoding

• Go github.com/traefik/traefik/v3: < 3.4.1 → fixed in 3.4.1 • Go github.com/traefik/traefik/v2: < 2.11.25 → fixed in 2.11.25 • Go github.com/traefik/traefik: <= 1.7.34 (no fix yet)

Impact There is a potential vulnerability in Traefik managing the requests using a `PathPrefix`, `Path` or `PathRegex` matcher. When Traefik is configured to route the requests to a backend using a matcher based on the path, if the URL contains a URL encoded string in its path, it’s possible to target a backend, exposed using another router, by-passing the middlewares chain. Example ```yaml apiVersion: traefik.io/v1alpha1 kind: IngressRoute metadata: name: my-service spec: routes: • match: PathPrefix(‘/service’) kind: Rule services: • name: service-a port: 8080 middlewares: • name: my-middleware-a • match: PathPrefix(‘/service/sub-path’) kind: Rule services: • name: service-a port: 8080 ``` In such a case, the request `http://mydomain.example.com/service/sub-path/%2e%2e/other-path` will reach the backend `my-service-a` without operating the middleware `my-middleware-a` unless the computed path is `http://mydomain.example.com/service/other-path` and should be computes by the first router (operating `my-middleware-a`). Patches • https://github.com/traefik/traefik/releases/tag/v2.11.25 • https://github.com/traefik/traefik/releases/tag/v3.4.1 For more information If you have any questions or comments about this advisory, please open an issue. Original Description Summary Path traversal with "/../" using URL encodings ("/%2e%2e") allows for circumventing routing rules. Details When having defined a route, you can path traverse using the URL encoded variant of /../ and reach endpoints that are not made publicly available. This issue has been found and fixed earlier with regular /../ and has been fixed in this CVE. This URL encoding trick works around that https://nvd.nist.gov/vuln/detail/CVE-2025-32431 Simply implementing a check on the URL encoding won't be sufficient as path traversal can take numerous formats. See examples here: https://book.hacktricks.wiki/en/pentesting-web/file-inclusion/index.html PoC Setup a service with two endpoints: "/public" and "/private", which returns a 200 OK for both Setup a Traefik proxy with a single route which points to the service using path /public Regular requests to traefik /public will return 200 OK and to /private should return 404 (response by Traefik) When making a request to /public/%2e%2e/private you should receive a 200 OK. Impact Impacts all traefik implementations with path prefix routes that expose only part of the downstream api Suggestion Provide configuration property which disables all path traversals. Steps: 1. Decode URL 2. Evaluate and construct relative path (do traversal before route evaluation) 3. Compare relative/evaluated path to configured routes (PathPrefix/pathRegexp)