You are running a version of MySQL which is older than version 3.23.56. It is vulnerable to a vulnerability that may allow the mysqld service to start with elevated privileges. An attacker can exploit this vulnerability by creating a DATADIR/my.cnf that includes the line 'user=root' under the '[mysqld]' option section. When the mysqld service is executed, it will run as the root user instead of the default user.
Upgrade to at least version 3.23.56