A remote code execution vulnerability exists in Microsoft SharePoint when the software fails to check the source markup of an application package. An attacker who successfully exploited the vulnerability could run arbitrary code in the context of the SharePoint application pool and server farm account. The security update addresses the vulnerability by correcting how SharePoint checks the source Marking of application packages. The vulnerability requires that a user uploads a specially crafted SharePoint app package to an affected version of SharePoint. The update fixes the vulnerability.”]
Source: https://msrc.microsoft.com/update-guide/vulnerability/CVE-2020-16952