Modbus is an industrial control system (ICS) network protocol that is used for communication between devices such as sensors, controllers, actuators, and monitors. Modbus has no inherent security functions on TCP port 502, which is the default port for Modbus TCP/IP communication. Modbus does not provide any encryption, authentication, or integrity protection for the data transmitted over the network, making it vulnerable to various attacks such as replay, modification, spoofing, or denial-of-service.