What’s Vulnerable › Vulnerabilities

CVE-2021-1691: Windows Hyper-V Denial of Service Vulnerability

• Severity: medium (CVSS 4.0 v2.0)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 4.1% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2021-01-12 · updated 2026-06-17

Description

Windows Hyper-V Denial of Service Vulnerability

Affected products

• Microsoft Windows 10 Version 1607: 20h2, 1909, 2004
• Microsoft Windows Server 2016: 20h2, 1909, 2004
• Microsoft Windows 10 1909: from 10.0.0 before publication — fixed in publication
• Microsoft Windows 10 2004: from 10.0.0 before publication — fixed in publication
• Microsoft Windows Server, version 1909 (Server Core installation): from 10.0.0 before publication — fixed in publication
• Microsoft Windows Server version 2004: from 10.0.0 before publication — fixed in publication
• Microsoft Windows Server version 20H2: from 10.0.0 before publication — fixed in publication

How to fix

Upgrade to a fixed version: Microsoft Windows 10 1909 publication; Microsoft Windows 10 2004 publication; Microsoft Windows Server, version 1909 (Server Core installation) publication; Microsoft Windows Server version 2004 publication; Microsoft Windows Server version 20H2 publication. Check the vendor advisory for mitigations.

References

• https://msrc.microsoft.com/update-guide/vulnerability/CVE-2021-1691
• https://portal.msrc.microsoft.com/en-US/security-guidance/advisory/CVE-2021-1691

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