This indicates an attack attempt to exploit a Command Injection vulnerability in PHP.
The vulnerability is due to insufficient validation on users' supplied inputs in the application when handling malicious requests. A remote attacker may be able to exploit this to execute arbitrary commands in the affected machine via crafted requests.
WebUI WebUI 1.5b9
System Compromise: Remote attackers can execute arbitrary commands in the context of the affected site
Currently we are unaware of any vendor supplied patch for this issue