CVE-2026-55040: critical vulnerability in Microsoft SharePoint Enterprise Server 2016
Microsoft SharePoint Server Security Feature Bypass Vulnerability
Published · Updated
Patch now. It under exploitation confirmed by CISA and has a working public exploit.
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.
Microsoft SharePoint has a weak authentication flaw that lets attackers bypass security protections remotely. This means unauthorized people could gain access to protected data and features without proper verification.
A weak authentication mechanism in Microsoft Office SharePoint allows network-based attackers to circumvent security controls without valid credentials. The vulnerability enables unauthorized access to restricted resources and functionality, requiring only network connectivity to the affected SharePoint instance.
In the same product, most dangerous first.