Port 5900 (TCP) — VNC

Virtual Network Computing remote desktop.

🔒 Runs locally — your input never leaves this browser tab

Often weak or no password. Tunnel over SSH or VPN.

Check if port 5900 is open

On the server, see what is listening:

sudo ss -tulpn | grep ':5900 '

From another machine, test reachability:

nc -zv your-server.example.com 5900

With UFW (Ubuntu/Debian):

sudo ufw deny 5900

With firewalld (RHEL/AlmaLinux/Rocky):

sudo firewall-cmd --permanent --remove-port=5900/tcp && sudo firewall-cmd --reload