MySQL Brute Force Defense
MySQL security hasn't been every a particular strong point of the server software. That is why most people recommend not expose the MySQL port outside the internal network/firewall. Like any other software, there has been records of vulnerabilities found.

Having said that, MySQL has a basic protection against port-scan attacks, as it maintains internally a list of blocked hosts and it adds a host to this list when more than 10/100 TCP/IP connections are interrupted (max_connect_errors). Please note that this is not a real brute-force attack protection, as both a successful and an unsuccessful complete connection will reset the counter and localhost is whitelisted.