This indicates an attack attempt to exploit a Buffer Overflow vulnerability in Oracle MySQL.
The vulnerability is due to an error when the vulnerable software parses a crafted Grant command. A remote attacker may be able to exploit this to execute arbitrary code within the context of the application, via a crafted request.
Oracle MySQL 5.5.28 and prior
System Compromise: Remote attackers can gain control of vulnerable systems.
Currently we are unaware of any vendor supplied patch or updates available for this issue.