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Researchers Disclose AI-Assisted SharePoint Exploit Chain Reaching Unauthenticated RCE
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
CVE-2026-63520: Microsoft SharePoint Remote Code Execution (FIXED)
Overview Rapid7 Labs conducted a zero-day research project against Microsoft SharePoint, resulting in the discovery of two new vulnerabilities that, when chained together, achieve unauthenticated remote code execution (RCE) against a vulnerable SharePoint server. Today, both Rapid7 and Microsoft are disclosing the second vulnerability in this chain, the RCE vulnerability CVE-2026-63520. The first vulnerability in the chain, CVE-2026-55040, was disclosed by Rapid7 and Microsoft last month. Our full disclosure timeline for the exploit chain can be seen below in Figure 1. Figure 1: The road to disclosure. ⠀ CVE-2026-63520 affects all supported versions of Microsoft SharePoint, and certain versions of Microsoft Project Server and Microsoft Office Web Apps Server. For the purpose of our research, we focused solely on SharePoint.
Rapid7 Analysis: Microsoft SharePoint JWT Token Authentication Bypass (CVE-2026-55040)
Overview On July 14, 2026, Rapid7 and Microsoft disclosed CVE-2026-55040, an authentication bypass vulnerability affecting Microsoft SharePoint. Today we are publishing a technical analysis of the vulnerability along with an accompanying proof-of-concept (PoC) script . Figure 1: The Rapid7 Labs PoC for CVE-2026-55040. ⠀ A remote unauthenticated attacker can leverage CVE-2026-55040 to bypass authentication on a vulnerable SharePoint server, and perform operations as a SharePoint site user or administrator. The vulnerability is due to several issues in the JWT token validation pipeline. Analysis The following technical analysis is based upon SharePoint Server Subscription Edition version 16. 0. 19725. 20210 . A critical authentication bypass vulnerability exists in SharePoint Server Subscription Edition's JWT token validation pipeline.
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