This indicates an attack attempt against a Remote Code Execution vulnerability in ZeroShell.
The vulnerability is due to insufficient sanitizing of user supplied inputs in the application when handling a crafted HTTP request. A remote attacker may be able to exploit this to execute arbitrary code within the context of the application, via a crafted HTTP request.
ZeroShell 1.0beta11 and earlier
System Compromise: Remote attackers can execute arbitrary code on vulnerable systems.
Apply the most recent upgrade or patch from the vendor.