Port 5900: VNC
Open VNC port detected on a publicly accessible host.
Severity: Critical | Port: 5900
What is VNC?
VNC (Virtual Network Computing) is a remote desktop sharing protocol that lets you view and control another computer's screen over a network. Unlike RDP which is Windows-specific, VNC works across operating systems. It is commonly used for remote support, server management, and accessing headless machines.
Why this is a problem
Many VNC implementations have weak or no authentication by default. Even when a password is set, VNC passwords are limited to 8 characters in some implementations and the protocol itself does not encrypt traffic (unless tunneled through SSH or VPN). An exposed VNC port gives attackers a direct path to attempt to gain full graphical control of the machine.
What you should do
- Close port 5900 to the internet — VNC should never be publicly accessible
- If remote desktop access is needed, tunnel VNC through SSH or a VPN
- Use a VNC implementation that supports strong authentication and encryption
- Consider switching to a more secure alternative like RDP (behind VPN) or a web-based remote access tool