CVE-2021-1691Network attack vector

Authenticated denial of service

Published Jan 12, 2021 · Updated Nov 19, 2024

Denial of service in Microsoft Hyper-V on affected Windows 10 and Windows Server releases allows remote authenticated users to interrupt the host. Microsoft has not published the affected component, crafted input, or incorrect operation that triggers the interruption. The record requires network access and low privileges and reports only an availability impact; it does not identify a crash, hang, or reboot.

CVSS severity7.7
High
EPSS probability3.77%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Denial of service in Microsoft Hyper-V on affected Windows 10 and Windows Server releases allows remote authenticated users to interrupt the host. Microsoft has not published the affected component, crafted input, or incorrect operation that triggers the interruption. The record requires network access and low privileges and reports only an availability impact; it does not identify a crash, hang, or reboot.

The record

CVE
CVE-2021-1691
Published
Jan 12, 2021
Updated
Nov 19, 2024
Vendor
Microsoft
Product
Windows 10 Version 1909
Classifications
T1499
Attack vector
network
Privileges
authenticated

Timeline

How it unfolded

  1. Jan 12, 2021CVE publishedPublication date reported by the CVE source.
  2. Nov 19, 2024Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=10.0.0 <publication

What conditions does exploitation require?

Attack vectornetwork
Required privilegesauthenticated

What is affected?

Microsoft · Windows 10 Version 1909version=10.0.0 <publication
Microsoft · Windows Server, version 2004version=10.0.0 <publication
Microsoft · Windows Server version 20H2version=10.0.0 <publication
Microsoft · Windows 10 Version 2004version=10.0.0 <publication
Microsoft · Windows Server, version 1909 (Server Core installation)version=10.0.0 <publication

Published CVSS scores

4.0NIST NVDAV:N/AC:L/Au:S/C:N/I:N/A:P
7.7Microsoft CorporationCVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:N/I:N/A:H

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

T1499Endpoint Denial of Service

Public exploit references

No public exploit references are available in this record.

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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