The remote host is vulnerable to a Denial of Service (DoS) attack.
The remote host is running Serv-U FTP server. There is a bug in the way this version handles the 'STOU' command, which is used to send files to a remote server. It is reported that Serv-U FTP server will crash if it receives certain 'STOU' requests. An attacker may connect to the remote server and issue a 'STOU' request to deny service to legitimate users.
Upgrade to version 18.104.22.168 or higher.