Modbus
Modbus
Modbus (Industrieprotokoll)
Modbus is one of the oldest and most widely used communication protocols of industrial automation. It is simple, robust and cross-vendor — and precisely for that reason ubiquitous to this day in controllers, sensors and actuators. It was, however, designed without any security function.
History & facts. Modbus stems from the late 1970s and has established itself as a de-facto standard because of its simplicity; it exists both in serial variants and over TCP/IP. Since it knows neither authentication nor encryption, anyone with access to the network can send commands or read values — a weakness that is grave in the OT context but inherent in the design. It implicitly trusts all participants.
Outlook & recommendation. Modbus can hardly be „made secure“ without replacing it; pragmatic protection therefore lies in the surroundings: strict network segmentation, controlled access and the monitoring of Modbus traffic for unexpected or anomalous commands. Because the protocol is so widespread, observing it is part of the standard repertoire of OT security. It is a prime example of why visibility and segmentation in OT are more important than the (often impossible) hardening of the protocol itself.