By Default, no IP Address is remotely allowed to access or authenticate to MySQL even if they try. Though, the ports will be open, but only the Internal Websites who has localhost access can connect to the Databases.
For any Other IP addresses to access any Databases, You need to login to respective cPanel account, Go to Remote MySQL and Allow Access of that specific or Subnet IP address. That too will only allow access of those databases belonging to that cPanel Account, Not the whole MySQL access.