Compares the detected service on a port against the expected service for that port number (e.g. ssh on 22, http on 80) and reports deviations. The script requires that a version scan has been run in order to be able to discover what service is actually running on each port.
nmap --script unusual-port <ip>
23/tcp open ssh OpenSSH 5.8p1 Debian 7ubuntu1 (protocol 2.0) |_unusual-port: ssh unexpected on port tcp/23 25/tcp open smtp Postfix smtpd
License: Same as Nmap--See https://nmap.org/book/man-legal.html