CVE-2026-55040
Microsoft SharePoint Weak Authentication Vulnerability
IN CISA KEV
Weak authentication in Microsoft Office SharePoint allows an unauthorized attacker to bypass a security feature over a network.
- Vendor
- Microsoft
- Product
- SharePoint
- CVSS 3.1
- 9.1 (critical), scored by secure@microsoft.comCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N
- CWE
- CWE-1390
- Published
- 2026-07-14
- NVD modified
- 2026-08-19
- NVD status
- Analyzed
CISA KEV
- Date added
- 2026-08-18
- Due date
- 2026-08-21
- Ransomware use
- Unknown
- 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.
EPSS
69.5% chance of exploitation in the next 30 days (percentile 99th)
FIRST EPSS, updated 17 Oct 2026. About EPSS
CVSS is severity, EPSS is likelihood, KEV means already exploited. EPSS is a statistical probability, not a certainty: a low score does not make a bug safe, and a high one does not prove it is being exploited.
References
- msrc.microsoft.com (Patch, Vendor Advisory)
- www.rapid7.com (US Government Resource)
Data last updated 18 Oct 2026. Sources: NVD API 2.0, CISA KEV catalog, FIRST EPSS. Links: NVD, CISA KEV. Metadata only. ThreatWire does not host exploit code.