I have a question concerning setting up a FTP server on a VPN connected host. Basically I have a FTP server setup on my machine that's behind a VPN through the VPN providers client. Everything works, so this isn't a question about that. But recently I've seen some activity on my FTP server from non connected users (not logged in) where they wrote the following command :
ftp GET / HTTP/1.0 and the server responded with my real hostname aka my real IP-adress even though the only way to connect to the FTP server itself is through my VPN static IPv4 adress. First off why is this possible? And how can I fix it? Did they just bypass the security of my VPN? And why are commands like these available without authorization?