Ubuntu Uncomplicated Firewall (ufw) rules to allow specific IP addresses to access VNC

vnc-security

## allow ssh connections (otherwise you will lock yourself out)
sudo ufw allow 22/tcp
## allow VNC connections from one IP address (edit the port if you don't use 5901)
sudo ufw allow from 12.34.56.78/24 to any port 5901
## reject all other incoming connections
sudo ufw default reject incoming
## enable the firewall
sudo ufw enable