A vulnerability exists in Mosquitto versions 0.15 to 1.4.11. Pattern based ACLs can be bypassed by clients that set their username/client id to # or +. This allows locally or remotely connected clients to access MQTT topics that they do have the rights to. The same issue may be present in third party authentication/access control plugins for Mosquitto. The vulnerability only comes into effect where pattern based ACLs are in use, or potentially where third party plugins are in use. Fixed In Version mosquitto 1.4.12 Reference Patch