T0869.002 Publish/Subscribe Protocols

Adversaries may communicate using publish/subscribe (pub/sub) application layer protocols to avoid detection/network filtering by blending in with existing traffic. Commands to the remote system, and often the results of those commands, will be embedded within the protocol traffic between the client and broker. Protocols such as MQTT are widely used in Internet-of-Things (IoT) and operational technology environments where devices are resource constrained and there is limited or unreliable network bandwidth. The protocol follows a publish/subscribe design, with message distribution managed by a centralized broker. Publishers categorize their messages by topics, while subscribers receive messages according to their subscribed topics. An adversary may abuse publish/subscribe protocols to communicate with systems under their control from behind a message broker while also blending in with normal, expected traffic.