This indicates an attack attempt to exploit a Security Bypass vulnerability in Microsoft Outlook.
The vulnerability is due to insufficient validation of emails that are sent to the application. A remote attacker may be able to exploit this to load crafted documents via outlook attachments, possibly leading to other attacks.
Microsoft Outlook 2007 Service Pack 3
Microsoft Outlook 2010 Service Pack 2 (32-bit editions)
Microsoft Outlook 2010 Service Pack 2 (64-bit editions)
Microsoft Outlook 2016 (32-bit edition)
Microsoft Outlook 2016 (64-bit edition)
Microsoft Outlook 2013 Service Pack 1 (32-bit editions)
Microsoft Outlook 2013 Service Pack 1 (64-bit editions)
Security Bypass: Remote attackers can bypass security features of vulnerable systems.
Apply the most recent upgrade or patch from the vendor.