Cross-site scripting (XSS) vulnerability in Microsoft Excel for Mac 2011 and Excel 2016 for Mac allows remote attackers to inject arbitrary web script or HTML via a crafted e-mail message that is mishandled by Outlook for Mac, aka "Microsoft Outlook for Mac Spoofing Vulnerability."
https://docs.microsoft.com/en-us/security-updates/securitybulletins/2015/ms15-116