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9.1 Critical Exploited

CVE-2026-55040 Microsoft SharePoint Weak Authentication Vulnerability

Active exploitation observed

· CISA KEV catalogue
Required action 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.
Ransomware campaigns Not observed so far
Weakness CWE-1390

Description

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

Affected products and versions

Product Affected versions Fixed in
Microsoft SharePoint Enterprise Server 2016 16.0 16.0.0 → < 16.0.5561.1001 16.0.5561.1001
Microsoft SharePoint Server 2019 16.0 16.0.0 → < 16.0.10417.20175 16.0.10417.20175
Microsoft SharePoint Server Subscription Edition 16.0 16.0.0 → < 16.0.19725.20434 16.0.19725.20434

References

Timeline

  1. Published
  2. Added to the KEV catalogue
  3. Last modified

Other CVEs of Microsoft SharePoint Enterprise Server 2016

The 337 CVEs of Microsoft SharePoint Enterprise Server 2016 →
CVE-2026-97783 Improper neutralization of input during web page generation ('cross-site scripting') in Microsoft Office SharePoint… 8.1 High CVE-2026-69943 Improper limitation of a pathname to a restricted directory ('path traversal') in Microsoft Office SharePoint allows… 8.8 High CVE-2026-62917 Improper input validation in Microsoft Office SharePoint allows an authorized attacker to perform spoofing over a… 4.6 Medium CVE-2026-58639 Server-side request forgery (ssrf) in Microsoft Office SharePoint allows an authorized attacker to perform spoofing over… 6.5 Medium
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