This indicates an attack attempt to exploit a remote Code Execution vulnerability in Microsoft IIS that was disclosed by Shadow Broker as EXPIREDPAYCHECK exploit.
The vulnerability is due to insufficient sanitizing 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.
Microsoft IIS 6.0
System Compromise: Remote attackers can gain control of vulnerable systems
Currently we are unaware of any vendor supplied patch for this issue