The MQTT protocol 3.1.1 requires a server to set a timeout value of 1.5 times the Keep-Alive value specified by a client, which allows remote attackers to cause a denial of service (loss of the ability to establish new connections), as demonstrated by SlowITe.

A specifically malformed MQTT Subscribe packet crashes MQTT Brokers using the mqtt-packet module versions < 3.5.1, 4.0.0 - 4.1.3, 5.0.0 - 5.6.1, 6.0.0 - 6.1.2 for decoding.

MQTT before 3.4.6 and 4.0.x before 4.0.5 allows specifically crafted MQTT packets to crash the application, making a DoS attack feasible with very little bandwidth.

MQTT.js 2.x.x prior to 2.15.0 issue in handling PUBLISH tickets may lead to an attacker causing a denial-of-service condition.