Rapid7 Labs disclosed an exploit chain combining two SharePoint vulnerabilities enabling unauthenticated RCE. CVE-2026-55040 (CVSS 9.1) is a JWT bypass; CVE-2026-63520 (CVSS 8.1) is an unsafe .NET instantiation flaw. Together, they enable arbitrary code execution as the SharePoint service account.
The research used AI agents across two sprints: January failed, March succeeded in 24 active days, 96 agentic sessions, 256 prompts, and roughly 80,000 tool calls.
The headline reads “AI found a critical vulnerability.” Rapid7’s analysis says otherwise. “An agent guided by a subject matter expert was crucial,” they write, specifically to prevent invalid assumptions. The AI accelerated the legwork; human expertise prevented dead ends. That reframes vulnerability research as human-guided AI augmentation, not autonomous discovery. The unexplained gap between January’s failure and March’s success (model quality? workflow?) is what actually deserves attention.
Sources: CVE-2026-55040: Microsoft SharePoint JWT Token Authentication Bypass Technical Analysis • CVE-2026-63520: Microsoft SharePoint Remote Code Execution
Coverage: Researchers Disclose AI-Assisted SharePoint Exploit Chain Reaching Unauthenticated RCE
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