This indicates an attack attempt to exploit a Memory Corruption vulnerability in Microsoft Office Excel.
The vulnerability is due to improper handling of objects while the vulnerable software attempts to access a specially crafted excel file. An attacker can exploit this to execute arbitrary code within the context of the logged in user via a crafted excel file.
Microsoft Excel 2010 Service Pack 2 (32-bit editions)
Microsoft Excel 2010 Service Pack 2 (64-bit editions)
Microsoft Excel 2013 Service Pack 1 (32-bit editions)
Microsoft Excel 2013 Service Pack 1 (64-bit editions)
Microsoft Excel 2013 RT Service Pack 1
Microsoft Excel 2016 (32-bit edition)
Microsoft Excel 2016 (64-bit edition)
Microsoft Excel 2016 for Mac
Microsoft Office Web Apps Server 2013 Service Pack 1
System Compromise: Remote attackers can gain control of vulnerable systems.
Apply the most recent upgrade or patch from the vendor.