Lakshminarayana, S.Santhi Thilagam, P.2026-02-032025IEEE Internet of Things Journal, 2025, 12, 12, pp. 22090-22109https://doi.org/10.1109/JIOT.2025.3549784https://idr.nitk.ac.in/handle/123456789/20473Message queuing telemetry transport (MQTT) has emerged as the widely adopted application layer protocol for IoT environments because of its lightweight header, minimal power, and bandwidth requirements. Despite its popularity, the earlier version of the protocol, MQTT v3.1.1, encounters performance issues in large-scale implementations and required an update to handle the growing requirements of modern IoT applications. In response to these concerns, MQTT v5.0 was released with several significant features designed to enhance the reliability, user experience, and performance of IoT systems. While the MQTT protocol features were intended to facilitate robust and efficient communications, adversaries could exploit these features to mount various types of attacks in IoT deployments. More specifically, the Denial-of-Service (DoS) attacks toward the MQTT protocol have recently gained a lot of attention from the research community. However, the existing works primarily focus only on exploring the possibilities of misusing the MQTT v3.1.1 protocol features to generate DoS attacks in IoT realms. In this work, we attempt to extensively investigate the advanced protocol features of MQTT v5.0 that can be exploited to launch DDoS attacks impacting the IoT paradigm. We present the first critical evaluation of Distributed DoS (DDoS) attacks on the MQTT v5.0 protocol by analyzing three significant features: 1) CONNECT properties; 2) user properties; and 3) flow control. Moreover, we systematically propose attack scenarios based on the adversary’s capabilities, thus illustrating the practicality of proposed attacks in real-world scenarios. Furthermore, we built a real-world testbed for IoT healthcare application to evaluate the severity of the identified attacks. The experimental results demonstrate the effectiveness of these attacks in impacting the availability of guaranteed IoT services to legitimate users, even in times of need. Additionally, we disclose the insightful findings of this work as takeaways and present research initiatives toward developing effective defense mechanisms for MQTT v5.0 protocol. We hope that such a discussion could pave the way for future research, contributing to MQTT v5.0 security and resiliency. © 2014 IEEE.Application LayerBandwidthDenial-of-service attackInternet protocolsNetwork layersQueueing networksQueueing theoryTelemeteringTelemetering systemsDenialof- service attacksDistributed denial of serviceDistributed denial of service attackInternet of thingMessage queuing telemetry transportMessage queuing telemetry transport brokerMessage queuing telemetry transport securityMessage queuing telemetry transport v5.0Transport protocolsTransport securityInternet of things