This indicates an attack attempt to exploit a remote Command Execution vulnerability in Sophos Web Appliance.
The vulnerability is due to insufficient sanitizing of user supplied inputs in the application when parsing HTTP request.
A remote attacker may be able to exploit this to execute arbitrary operating system command within the context of the application, via a crafted HTTP request.
Sophos Web Appliance 18.104.22.168
System Compromise: Remote attackers can gain control of vulnerable systems.
Apply the most recent upgrade or patch from the vendor.