Security experts from Trend Micro and the Polytechnic University of Milan studied machine-to-machine (M2M) protocols. M2M protocols can be abused to attack IoT and industrial Internet of Things (IIoT) systems. The experts analyzed the Message Queuing Telemetry Transport (MQTT) and Constrained Application Protocol (CoAP) Protocol. MQTT is a messaging protocol used to establish communication between broker and multiple clients. CoAP is a UDP client-server protocol that allows communications between nodes.”]
Source: https://securityaffairs.co/wordpress/78677/hacking/m2m-protocols-flaws.html