CVE-2026-63520: Microsoft SharePoint Remote Code Execution (FIXED)

OverviewRapid7 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. An attacker can leverage CVE-2026-63520 to execute arbitrary code on a vulnerable SharePoint server with the privileges of the SharePoint Site’s service account. The vulnerability is due to an unsafe .NET type instantiation issue within the Business Connectivity Services.CVE-2026-63520 has a CVSSv3.1 score of 8.1 (High), and a Common Weakness Enumeration (CWE) of CWE-20: Improper Input Validation. While the severity of the RCE is described as high, chained together with CVE-2026-55040 it becomes part of a critical u…