This indicates an attack attempt to exploit a Cross-Site Scripting vulnerability in Microsoft Exchange Server.
The vulnerability is due to Microsoft Exchange Server does not properly validate the OWA request. An attacker who successfully exploited these vulnerabilities can execute arbitrary script code within the context of the application.
Microsoft Exchange Server 2007 Service Pack 3
Microsoft Exchange Server 2010 Service Pack 3
Microsoft Exchange Server 2013 Service Pack 1
Microsoft Exchange Server 2013 Cumulative Update 6
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.