CVE-2020-16951: 
vulnerability analysis and mitigation

A remote code execution vulnerability (CVE-2020-16951) exists in Microsoft SharePoint when the software fails to check the source markup of an application package. The vulnerability was disclosed and patched as part of Microsoft's October 2020 Patch Tuesday update (Tenable Blog, NVD).

The vulnerability occurs due to SharePoint's failure to properly validate the source markup of application packages. The vulnerability has a CVSS v3.1 base score of 7.8 HIGH (CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H) according to NVD, while Microsoft assigned it a score of 8.6 HIGH (CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:H/A:L) (NVD).

Successful exploitation of this vulnerability could allow an attacker to run arbitrary code in the context of the SharePoint application pool and the SharePoint server farm account, potentially leading to a complete compromise of the affected SharePoint server (NVD).

To exploit this vulnerability, an attacker would need to upload a specially crafted SharePoint application package to an affected version of SharePoint. The vulnerability affects multiple versions of SharePoint, including SharePoint Enterprise Server 2016, SharePoint Foundation 2013 SP1, and SharePoint Server 2019 (NVD).

Microsoft addressed this vulnerability by correcting how SharePoint checks the source markup of application packages. The fix was released as part of the October 2020 security updates. Organizations are advised to apply the security update to affected SharePoint installations (NVD).