GitHub Security Advisory: GHSA-vrch-868g-9jx5
Package: github.com/traefik/traefik/v2 (GO)
Severity: LOW (CVSS 0.0)
CWE: CWE-22: Improper Limitation of a Pathname to a Restricted Directory ('Path Traversal')
Vulnerable versions: < 2.11.25
Patched in: 2.11.25

Summary: Traefik allows path traversal using url encoding

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

<details>
<summary>Original Description</summary>
### 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)
</details>