CVE-2021-24086Public exploitNetwork attack vector

Remote system crash via IPv6 fragment reassembly

Published Feb 25, 2021 · Updated Aug 3, 2024

Denial of service in Microsoft Windows TCP/IP allows remote attackers to crash affected systems with crafted IPv6 fragments. In tcpip.sys, Ipv6pReassembleDatagram truncates the allocation length, accepts a null NdisGetDataBuffer result, and writes through it. IPv6 reachability is required, and successful exploitation produces a stop error that interrupts the operating system.

CVSS severity7.5
High
EPSS probability58.96%
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 Windows TCP/IP allows remote attackers to crash affected systems with crafted IPv6 fragments. In tcpip.sys, Ipv6pReassembleDatagram truncates the allocation length, accepts a null NdisGetDataBuffer result, and writes through it. IPv6 reachability is required, and successful exploitation produces a stop error that interrupts the operating system.

The record

CVE
CVE-2021-24086
Published
Feb 25, 2021
Updated
Aug 3, 2024
Vendor
Microsoft
Product
Windows 10 Version 1507
Classifications
T1499
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Feb 25, 2021CVE publishedPublication date reported by the CVE source.
  2. Aug 3, 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 privilegesunauthenticated

What is affected?

Microsoft · Windows 10 Version 1507version=10.0.0 <publication
Microsoft · Windows Server 2019version=10.0.0 <publication
Microsoft · Windows 7version=6.1.0 <publication
Microsoft · Windows 10 Version 1909version=10.0.0 <publication
Microsoft · Windows 10 Version 1803version=10.0.0 <publication
Microsoft · Windows 8.1version=6.3.0 <publication
Microsoft · Windows Server 2016 (Server Core installation)version=10.0.0 <publication
Microsoft · Windows Server 2012 (Server Core installation)version=6.2.0 <publication
Microsoft · Windows Server 2012version=6.2.0 <publication
Microsoft · Windows Server, version 2004version=10.0.0 <publication
Microsoft · Windows Server 2016version=10.0.0 <publication
Microsoft · Windows Server 2008 R2 Service Pack 1version=6.1.0 <publication
Microsoft · Windows 10 Version 20H2version=10.0.0 <publication
Microsoft · Windows Server 2008 R2 Service Pack 1 (Server Core installation)version=6.0.0 <publication
Microsoft · Windows Server 2012 R2 (Server Core installation)version=6.3.0 <publication
Microsoft · Windows Server 2019 (Server Core installation)version=10.0.0 <publication
Microsoft · Windows 7 Service Pack 1version=6.1.0 <publication
Microsoft · Windows Server version 20H2version=10.0.0 <publication
Microsoft · Windows 10 Version 1607version=10.0.0 <publication
Microsoft · Windows Server 2008 Service Pack 2version=6.0.0 <publication
Microsoft · Windows 10 Version 2004version=10.0.0 <publication
Microsoft · Windows 10 Version 1809version=10.0.0 <publication
Microsoft · Windows Server 2012 R2version=6.3.0 <publication
Microsoft · Windows Server 2008 Service Pack 2 (Server Core installation)version=6.0.0 <publication
Microsoft · Windows Server, version 1909 (Server Core installation)version=10.0.0 <publication

Published CVSS scores

7.5NIST NVDCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/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
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitPublished

Weakness, pattern, technique

T1499Endpoint Denial of Service

Public exploit references

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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