Traefik has a possible vulnerability with its path matchers

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 /../ in its path, it’s possible to target a backend, exposed using another router, by-passing the middlewares chain.

Example

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/../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/v2.11.24
• https://github.com/traefik/traefik/releases/tag/v3.3.6
• https://github.com/traefik/traefik/releases/tag/v3.4.0-rc2

Workaround

Add a PathRegexp rule to the matcher to prevent matching a route with a /../ in the path.

Example:

match: PathPrefix(`/service`) && !PathRegexp(`(?:(/\.\./)+.*)`)

For more information

If you have any questions or comments about this advisory, please open an issue.