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CVE-2026-55040

Microsoft SharePoint Weak Authentication Vulnerability

Microsoft SharePoint CWE-1390

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

CVSS Score
9.1
Critical
EPSS — Exploit Probability
70%
Riskier than 99% of all CVEs · checked 2026-10-13
Exploitation
Confirmed in the wild
KEV since 2026-08-18
Remediation
Patch available
Federal deadline 2026-08-21
CISA 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. Deadline for federal agencies: 2026-08-21.

NVD entry Vendor patch PoC / advisory CISA KEV

16 articles across 6 outlets · first covered Jul 15, 2026 · latest Oct 2, 2026

Associated threat actors

FIN11

Coverage timeline

Related CVEs — Microsoft

CVE-2026-96940 CVE-2026-32201KEV CVE-2026-45659KEV CVE-2026-56164KEV CVE-2026-50522KEV CVE-2026-58644KEV CVE-2026-65660KEV CVE-2026-85880KEV