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.