CVE intelligenceCISA KEV

CVE-2026-55040

Microsoft SharePoint Weak Authentication Vulnerability

Published Jul 14, 2026Sources checked Nov 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.

Public exploit: Public PoC reported.

The Hacker News: Exploitation attempts reported by The Hacker News (2026-08-13)
The Hacker News reports attacks targeting CVE-2026-55040. The collected report supports exploitation attempts; it does not establish successful compromise.
The Hacker News: Public proof of concept reported by The Hacker News (2026-08-13)
The Hacker News reports a public proof of concept for CVE-2026-55040. This is a publication report; SecurityAlert has not run or validated the code.

What to do next

Remediation and response

Review the linked vendor advisory and apply the mitigation or fixed release for your affected product.

Microsoft Security Response Center guidance

Vendor revision: Jul 14, 2026

Install KB5002891. Install KB5002883. Install KB5002882.

Vendor-listed releases

16.0.5561.1001
16.0.10417.20175
16.0.19725.20434

CISA KEVListedObserved exploitation

EPSS69.5%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.

Source: NVD

Reported activity: The Hacker News reports attacks targeting CVE-2026-55040. The collected report supports exploitation attempts; it does not establish successful compromise.
The Hacker News · Published Aug 13, 2026

CISA says: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 catalog due date Aug 21, 2026