All vulnerabilities
CVE-2026-55040

Microsoft SharePoint Weak Authentication Vulnerability

Microsoft SharePointApplications & CMS
Open in ThreatlineRecord JSON
CVSS
9.1Critical
ExploitationExploited in the wildAdded to KEV 18 Aug 2026CISA KEV
Exploit odds (EPSS)69.5%Chance of exploitation activity in the next 30 days, higher than 99% of CVEs. Scored 23 Oct 2026FIRST EPSS
Fixed in16.0.5561.1001Also 16.0.10417.20175, 16.0.19725.20434CVE List
Federal deadline21 Aug 2026Remediation due date for US federal agenciesCISA KEV
CISA required actionApply 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 KEV
Patching is not enoughCISA requires federal agencies to look for signs of compromise on affected systems, not only patch (forensic triage under BOD 26-04). Treat exposed systems as possibly compromised. CISA guidance

What fixes it

  • 16.0.5561.1001Microsoft SharePoint Enterprise Server 2016CVE List
  • 16.0.10417.20175Microsoft SharePoint Server 2019CVE List
  • 16.0.19725.20434Microsoft SharePoint Server Subscription EditionCVE List

A fixed version on one release line is not the upgrade target for every line. Check your exact version and any vendor backports.

Timeline

  1. 14 Jul 2026, 17:09 UTCPublishedCVE List
  2. 18 Aug 2026Added to CISA KEVCISA KEV

Public exploit code and templates 1

  • Scanner templateMicrosoft SharePoint Server - JWT Authentication BypassNuclei

Listed so defenders can prioritize. Threatline links to the source and does not host exploit code.

Description

Microsoft SharePoint contains a weak authentication vulnerability which allows an unauthorized attacker to bypass a security feature over a network.

Text from CVE List

Affected versions 3

  • Microsoft SharePoint Enterprise Server 2016affected: 16.0.0 before 16.0.5561.1001CVE List
  • Microsoft SharePoint Server 2019affected: 16.0.0 before 16.0.10417.20175CVE List
  • Microsoft SharePoint Server Subscription Editionaffected: 16.0.0 before 16.0.19725.20434CVE List

References 5