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CVE-2026-55040: Microsoft SharePoint Weak Authentication Vulnerability

Microsoft SharePoint · in CISA KEV since 2026-08-18

2026-08-18added to KEV

2026-08-21federal remediation due date

50.59%EPSS exploit probability (30 days) 98.9th percentile

9.1 CRITICALCVSS 3.1

Unknownknown ransomware use

35days from NVD publication to KEV

What it is

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

Required action (CISA)

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.

CWE	CWE-1390
CVSS vector	`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N`
NVD published	2026-07-14 (Analyzed)

Original records: NVD · CISA KEV · JSON: /api/cve/CVE-2026-55040.json · all KEV CVEs

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