I'm slightly concerned that this could also be open and internet facing
By "this" do you mean 127.0.0.1 (port 8777) or the proxy's internet facing side?
The loopback range 127.0.0.0/8 is supposed to be dropped if any of those packets should get on the network. Those packets are not supposed to be on the network.
The proxy's internet facing side ... if the proxy were keeping listening ports open you could check it out by doing a netstat -ano and seeing what ports are listening, cull out the known ones, and investigate the unknown ones.