This indicates an attack attempt to exploit a Cross-Site Scripting vulnerability in Microsoft Sharepoint.
The vulnerability is due to insufficient sanitizing of user supplied inputs in the application when handling a crafted request. A remote attacker may be able to exploit this to execute arbitrary script code within the context of the application.
Microsoft SharePoint Server 2013
Microsoft SharePoint Server 2010
System Compromise: Remote attackers can execute arbitrary script code in the context of the application.
Apply the most recent upgrade or patch from the vendor.