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← archiveexploit · 27 Sep 2026 · 14:17 UTC

Rapid7 Analysis: Microsoft SharePoint JWT Token Authentication Bypass (CVE-2026-55040)

EXPLKEV575 CVEsource · RPD
KEVActive exploitation (KEV)

CISA KEV means this flaw has been seen exploited in real attacks — not predicted, observed. Treat it as urgent regardless of its score.

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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. …

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