CVE-2026-55040: Microsoft SharePoint JWT Token Authentication Bypass (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 first vulnerability in this chain, the authentication bypass vulnerability CVE-2026-55040. The RCE component of the exploit chain is expected to be patched by Microsoft in the next update cycle for August 2026.