Hello,
You can configure it with no exec command - it will disable the command line interpreter on this connection. Even if someone connects to the AUX port, the port will appear "dead".
This being said, I do not believe that it is wise to disable the AUX port functionality. To use the AUX, you need physical access to the switch - and if you have a physical access to the switch, then you can also access the console port, the AUX port, the management Ethernet interface directly, you can even change the cabling or smash the box completely so you can do much more harm. Disabling the AUX port does not add to the security.
I would personally recommend configuring it the same way as the console port. This way, if something happens to the console port (such as burning out due to some static electricity discharge), you can still use AUX to connect to the box.
Best regards,
Peter
