If you run Mosquitto without a configuration file then it will allow unauthenticated access but on localhost only. The same is true if you have a configuration file but do not define a listener.
If you want to allow connections from other computers, you must define a listener and define some form of authentication. That could be password file based authentication, the dynamic security plugin, or allowing unauthenticated access with the allow_anonymous true option. »
etc. Dont acte !