Researchers Disclose AI-Assisted SharePoint Exploit Chain Reaching Unauthenticated RCE

Researchers discovered a critical vulnerability chain in Microsoft SharePoint on-premises servers that allows attackers without valid credentials to gain administrative access and run malicious code. The flaw was found partly through an AI agent that performed automated code analysis, chaining together two vulnerabilities (CVE-2026-55040 with CVSS 9.1 and CVE-2026-63520 with CVSS 8.1, a rating system measuring vulnerability severity) in SharePoint's authentication and service systems. The attack affects SharePoint Server Subscription Edition, 2019, and 2016, but not the cloud-based SharePoint Online.