CVE-2026-55040: Microsoft SharePoint Weak Authentication Vulnerability

Critical severity, CVSS 9.1. Actively exploited: in CISA KEV since 2026-08-18. EPSS: 69.5% chance of exploitation in the next 30 days.

Weak authentication in Microsoft Office SharePoint allows an unauthorized attacker to bypass a security feature over a network.

Affected products

• Microsoft SharePoint Server: before 16.0.19725.20434 (fixed in 16.0.19725.20434); version 2016 only; version 2019 only

Published 2026-07-14. Last modified 2026-08-19.