This indicates an attack attempt against a Command Injection vulnerability in Sophos Web Appliance.
The vulnerability is caused by lacking of sanitizing the parameter "unblockip" and "blockip" that is passed to "MgrReport.php". A remote attacker can exploit this to execute arbitrary commands, via a crafted request.
Sophos Web Appliance 188.8.131.52 and the prior
System Compromise: Remote attackers can gain control of vulnerable systems.
Apply the most recent upgrade or patch from the vendor.