This indicates an attack attempt to exploit an Use After Free vulnerability in Microsoft Office.
The vulnerability is due to an error when the vulnerable software handles a maliciously crafted xls file. A remote attacker may be able to exploit this to execute arbitrary code within the context of the application, via a crafted xls file.
Microsoft Office 2016 Click-to-Run (C2R) for 32-bit editions
Microsoft Office 2016 Click-to-Run (C2R) for 64-bit editions
System Compromise: Remote attackers can gain control of vulnerable systems.
Apply the most recent upgrade or patch from the vendor.