Executive Summary
Researchers, working largely through an AI agent, found CVE-2026-55040 (CVSS 9.1), a SharePoint flaw letting anyone sign in as any user including admin without a valid account, leading to unauthenticated RCE.
What Happened
Security researchers found a way to enter Microsoft SharePoint servers as any user, including an administrator, with no valid account. A significant part of the work that found it was done through an AI agent. The flaw, tracked as CVE-2026-55040 (CVSS 9.1), affects SharePoint Server Subscription Edition, SharePoint Server 2019, and SharePoint Server 2016. Microsoft's
Affected Products
- SharePoint Server Subscription Edition
- SharePoint Server 2019
- SharePoint Server 2016
Vulnerability / Attack Technique
Authentication bypass chained to RCE, found with AI assistance
Technical Mechanism
The chain lets an unauthenticated attacker act as any user, including administrator, and execute code.
AI Security Category
AI-assisted attack
Part of the AI-Assisted Attacks topic.
Relevant Frameworks
RealGround Analysis
AI agents are now doing substantial vulnerability research on enterprise software. RealGround analysis: expect faster discovery of critical flaws in widely deployed platforms.
Recommended Controls
- Apply Microsoft's SharePoint update
- Do not expose on-prem SharePoint to the internet
Related RealGround Service
Secure AI Agent Build · or start with the free AI Agent Security Scanner.
Sources
thehackernews.com: https://thehackernews.com/2026/08/researchers-disclose-ai-assisted.html
Summary and analysis written by RealGround from the source above; last updated 2026-10-18.