Authenticated code execution via unsafe deserialization

Deserialization of untrusted data in Microsoft SharePoint Server 2019 and Subscription Edition allows remote authenticated users to execute code over a network. Microsoft has publicly described the flaw only as unsafe deserialization in Office SharePoint and has not disclosed the vulnerable endpoint, object type, or code path that rebuilds attacker-controlled data. Exploitation requires valid SharePoint credentials with low privileges and no user interaction, so exposure is limited to reachable on-premises farms that permit untrusted authenticated access.