This indicates an attack attempt to exploit a remote OS Command Execution vulnerability in D'Link wireless router.
The vulnerability is due to insufficient sanitizing of user supplied inputs in the application when handling crafted HTTP requests. A remote attacker may be able to exploit this to execute arbitrary OS command within the context of the application, via a crafted HTTP request.
DIR-615 - Hardware revision D3
DIR-300 - Hardware revision A
System Compromise: Remote attackers can gain control of vulnerable systems.
Apply the most recent upgrade or patch from the vendor.