In computing, Virtual Network Computing (VNC) is a graphical desktop-sharing system that uses the Remote Frame Buffer protocol (RFB) to remotely control another computer. It transmits the keyboard and mouse events from one computer to another, relaying the graphical-screen updates back in the other direction, over a network. From wikipedia.
VNC usually uses ports 5800 or 5801 or 5900 or 5901.
PORT STATE SERVICE5900/tcp open vnc
nmap -sV --script vnc-info,realvnc-auth-bypass,vnc-title -p <PORT> <IP>msf> use auxiliary/scanner/vnc/vnc_none_auth
vncviewer [-passwd passwd.txt] <IP>::5901
Default password is stored in: ~/.vnc/passwd
If you have the VNC password and it looks encrypted (a few bytes, like if it could be and encrypted password). It is probably ciphered with 3des. You can get the clear text password using https://github.com/jeroennijhof/vncpwd
makevncpwd <vnc password file>
You can do this because the password used inside 3des to encrypt the plain-text VNC passwords was reversed years ago. For Windows you can also use this tool: https://www.raymond.cc/blog/download/did/232/ I save the tool here also for ease of access: