I could be wrong, buy my understanding is that it isn't even a door. It simply allows anyone that has a certain private key, to send a payload that the server will execute. This won't produce any audit of someone logging in, you won't see any session etc.

Any Linux with this installed would basically become a bot that can be taken over. Perhaps they could send a payload to make it DDoS another host, or payload to open a shell or payload that would install another backdoor with more functionality, and to draw attention away from this one.