Threat Summary Cybersecurity and Infrastructure Security Agency (CISA) has added several critical zero-day vulnerabilities targeting Microsoft SharePoint Server. CVE-2026-58644 is a deserialization flaw in SharePoint Server (Subscription Edition <16.0.19725.20434; 2019 <16.0.10417.20175; 2016 <16.0.5561.1001) that allows remote, authenticated attackers to execute arbitrary code, gain persistence (historically through IIS machine key theft), and establish footholds in enterprise ... UPDATE: Microsoft SharePoint Server Vulnerabilities – Immediate Patching Required