CVE intelligenceCISA KEV

CVE-2026-55040

Microsoft SharePoint Weak Authentication Vulnerability

Published Jul 14, 2026Sources checked Sep 12, 2026

9.1CRITICALCVSS out of 10

What this means

Actively exploited

CISA lists CVE-2026-55040 in its Known Exploited Vulnerabilities catalog, which means exploitation has been observed. The entry applies to Microsoft SharePoint.

Apply mitigations in accordance with vendor instructions, ensuring compliance with CISA’s BOD 26-04 Prioritizing Security Updates Based on Risk (see URL in Notes) guidance and CISA’s “Forensics Triage Requirements” (see URL in Notes). Follow applicable BOD 26-04 guidance for cloud services or discontinue use of the product if mitigations are unavailable. Stakeholders are responsible for evaluating each asset's internet exposure and ensuring adherence to BOD 26-04 patching guidelines.

CISA KEVListedObserved exploitation

EPSS50.6%Estimated 30-day exploitation probability

Ransomware useNot markedCISA KEV ransomware field

Threat actors1Source-linked actor relationships

Overview

What is CVE-2026-55040?

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