This indicates an attack attempt to exploit a Command Injection vulnerability in PHPWiki SyntaxHighlighter Plugin.
The vulnerability is due to insufficient validation of user supplied inputs in the application. A remote attacker may be able to exploit this to execute arbitrary code within the context of the application, via a crafted HTTP request.
PhpWiki before 1.5.5
System Compromise: Remote attackers can gain control of vulnerable systems.
Apply the most recent upgrade or patch from the vendor: