Main Vulnerability Database Vulnerabilities #VU138275

Weak Authentication in Microsoft SharePoint Server - CVE-2026-55040

Published: July 17, 2026 / Updated: August 14, 2026

Vulnerability identifier: #VU138275

CSH Severity: Critical

CVSS v4: 9.3 [CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:H/VA:N/SC:N/SI:N/SA:N]

CVE-ID: CVE-2026-55040

CWE-ID: CWE-1390

Exploitation vector: Remote access

Exploit availability: The vulnerability is being exploited in the wild

Vulnerability details

The vulnerability allows a remote attacker to bypass an authentication security feature.

The vulnerability exists due to weak authentication in Microsoft Office SharePoint when handling network requests. A remote attacker can make an anonymous connection to bypass an authentication security feature.

Successful exploitation can allow impersonation, disclosure of files, and modification of data.

Affected software

Microsoft SharePoint Server

How to mitigate CVE-2026-55040

Install security update from vendor's website.

Microsoft SharePoint Server - addressed in versions 16.0.5561.1001, 16.0.10417.20175, 16.0.19725.20434

Links to Public Exploits and PoC-codes

Exploit #12935 - CVE-2026-55040 (Exploit code for CVE-2026-55040, it can create auth header for any validate account.) (August 14, 2026)

External References

Related Security Bulletins

Multiple vulnerabilities in Microsoft SharePoint Server