Patch nowWhy this label: EPSS 70%

CVE-2026-55040Microsoft SharePoint Weak Authentication Vulnerability

Product: Microsoft SharePoint
Added to CISA KEV: August 18, 2026
Deadline for US federal agencies: August 21, 2026
Known ransomware use: Not known
EPSS, next 30 days: 70%, in the top 1% of scored CVEs (Oct 25, 2026)
Weakness: CWE-1390

What CISA says

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

What CISA asks you to do

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.

Sources

Also exploited recently

Data from CISA's Known Exploited Vulnerabilities catalog (public domain) and FIRST EPSS, refreshed hourly. Rheono did not find or test this vulnerability; this page summarizes public sources.