This indicates an attack attempt against a remote Code Execution vulnerability in Microsoft Office.
The vulnerability is caused by an error when the vulnerable software handles a specially crafted rtf file. A remote attacker may be able to exploit this to execute arbitrary code within the context of the application, via a crafted RTF file.
Microsoft Office 2007 Service Pack 3
Microsoft Office 2010 Service Pack 2 (32-bit editions)
Microsoft Office 2010 Service Pack 2 (64-bit editions)
Microsoft Office 2013 Service Pack 1 (32-bit editions)
Microsoft Office 2013 Service Pack 1 (64-bit editions)
Microsoft Excel 2013 RT Service Pack 1
Microsoft Office 2016 (32-bit edition)
Microsoft Office 2016 (64-bit edition)
System Compromise: Remote attackers can gain control of vulnerable systems.
Apply the most recent upgrade or patch from the vendor.