This indicates an attack attempt to exploit a remote Code Execution vulnerability in Oracle MySQL.
The vulnerability is due to insufficient checks when handling the config file used by mysqld_safe. A remote attacker may be able to exploit this to execute arbitrary code on vulnerable systems via a crafted sql query.
MySQL version 5.7.15 and earlier versions
MySQL version 5.6.33 and earlier versions
MySQL version 5.5.52 and earlier versions
System Compromise: Remote attackers can gain control of vulnerable systems.
Currently we are unaware of any vendor supplied patch for this issue.