This indicates an attack attempt to exploit a Code Execution vulnerability in Microsoft SQL Server Reporting Services.
The vulnerability is caused by an error when the vulnerable software handles a specially crafted user-supplied script. A remote attacker may be able to exploit this to execute arbitrary code within the context of the application.
Microsoft SQL Server 2012 Service Pack 4
Microsoft SQL Server 2014 Service Pack 3
Microsoft SQL Server 2016 Service Pack 2 for x64-based Systems
System Compromise: Remote attackers can gain control of vulnerable systems.
Apply the most recent upgrade or patch from the vendor.