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

Detailed vulnerability description

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.

How to mitigate CVE-2026-55040

Sources

• https://portal.msrc.microsoft.com/en-US/security-guidance/advisory/CVE-2026-55040
• https://support.microsoft.com/help/5002891