5900 - VNC

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

Nmap:

Script: vnc-info

Example Usage

nmap -p 5901 --script vnc-info 192.168.0.50

PORT    STATE SERVICE 
5900/tcp open  vnc 
| vnc-info: 
|   Protocol version: 3.889 
|   Security types: 
|     Mac OS X security type (30) 
|_    Mac OS X security type (35) 

Connect to VNC:

vncviewer $IP:5901

Brute Force with Metasploit

use auxiliary/scanner/vnc/vnc_login