In Traefik before versions 1.7.26, 2.2.8, and 2.3.0-rc3, there exists a potential open redirect vulnerability in Traefik's handling of the "X-Forwarded-Prefix" header. The Traefik API dashboard component doesn't validate that the value of the header "X-Forwarded-Prefix" is a site relative path and will redirect to any header provided URI. Successful exploitation of an open redirect can be used to entice victims to disclose sensitive information. Active Exploitation of this issue is unlikely as it would require active header injection, however the Traefik team addressed this issue nonetheless to prevent abuse in e.g. cache poisoning scenarios.
Affected: Go: github.com/traefik/traefik, Go: github.com/traefik/traefik/v2, Go: github.com/containous/traefik, Go: github.com/containous/traefik/v2, Go: github.com/traefik/traefik/api, Go: github.com/traefik/traefik/v2/pkg/api, Go: github.com/containous/traefik/api, Go: github.com/containous/traefik/v2/pkg/api
## Summary
There exists a potential open redirect vulnerability in Traefik's handling of the `X-Forwarded-Prefix` header. Active Exploitation of this issue is unlikely as it would require active header injection, however the Traefik team addressed this issue nonetheless to prevent abuse in e.g. cache poisoning scenarios.
## Details
The Traefik API dashboard component doesn't validate that the value of the header `X-Forwarded-Prefix` is a site relative path and will redirect to any header provided URI.
e.g.
``` $ curl --header 'Host:traefik.localhost' --header 'X-Forwarded-Prefix:https://example.org' 'http://localhost:8081' <a href="https://example.org/dashboard/">Found</a>.` ```
### Impact A successful exploitation of an open redirect can be used to entice victims to disclose sensitive information.
### Workarounds
By using the `headers` middleware, the request header `X-Forwarded-Prefix` value can be overridden by the value `.` (dot)
- https://docs.traefik.io/v2.2/middlewares/headers/#customrequestheaders - https://docs.traefik.io/v1.7/basics/#custom-headers
### For more information
If you have any questions or comments about this advisory, open an issue in [Traefik](https://github.com/containous/traefik/issues).
## Credit
This issue was found by the GitHub Application Security Team and reported on behalf of the GHAS by the GitHub Security Lab Team.