The port that should be disabled on the firewall is port 3389. Port 3389 is used by Remote Desktop Protocol (RDP), which is a protocol that allows remote access and control of a Windows system through a graphical user interface. RDP can pose a security risk if it is not properly configured or secured, as it can expose the system to unauthorized or malicious access from external sources. Therefore, port 3389 should be disabled on the firewall unless it is needed for legitimate purposes.