Affected: Microsoft Skype for Business Server 2019 CU2, Microsoft Skype for Business Server 2015 CU 8, Microsoft Lync Server 2013, Microsoft SharePoint Enterprise Server 2016, Microsoft SharePoint Server 2019, Microsoft SharePoint Foundation 2013 Service Pack 1

An elevation of privilege vulnerability exists when Microsoft SharePoint Server and Skype for Business Server improperly handle OAuth token validation. An attacker who successfully exploited the vulnerability could bypass authentication and achieve improper access. To exploit this vulnerability, an attacker would need to modify the token. The update addresses the vulnerability by modifying how Microsoft SharePoint Server and Skype for Business Server validate tokens.