This indicates an attack attempt to exploit a Command Execution vulnerability in Trend Micro InterScan Web Security Virtual Appliance.
The vulnerability is due to improper validation of the HTTP request parameters. A remote attacker may be able to exploit this to execute arbitrary command within the context of the process, via a crafted HTTP request.
Trend Micro InterScan Web Security Virtual Appliance 6.5 prior to 6.5 CP 1746
System Compromise: Remote attackers can execute arbitrary command execution under the security context of the root user.
Apply the most recent upgrades or patches from the vendor.