Containous Traefik 1.6.x before 1.6.6, when --api is used, exposes the configuration and secret if authentication is missing and the API's port is publicly reachable.
https://github.com/containous/traefik/releases/tag/v1.6.6
https://github.com/containous/traefik/pull/3790/commits/368bd170913078732bde58160f92f202f370278b
https://github.com/containous/traefik/pull/3790/commits/113250ce5735d554c502ca16fb03bb9119ca79f1