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**Name of the Vulnerable Software and Affected Versions** SharePoint Enterprise Server 2016 SharePoint Server 2019 SharePoint Server Subscription Edition **Description** An issue exists in the deserialization mechanism of Microsoft Office SharePoint, where the deserialization of untrusted data allows an authorized attacker to execute arbitrary code remotely over a network. An attacker requires only Site Member permissions, with no elevated privileges or user interaction needed, and the flaw is exploitable from the internet. This issue has been actively exploited in the wild and can lead to full system compromise, data exfiltration, and serve as a pivot point for further network penetration. **Recommendations** Apply the security updates released by Microsoft on May 21, 2026, for SharePoint Enterprise Server 2016, SharePoint Server 2019, and SharePoint Server Subscription Edition. Audit Site Member permissions to minimize the risk of exploitation.