CVE-2021-40444Known exploitationPublic exploit

Code execution via ActiveX CAB path traversal

Published Sep 15, 2021 · Updated Aug 10, 2026

Remote code execution in MSHTML in Microsoft Windows allows remote attackers to run code through a crafted Office document. A crafted document makes the browser rendering engine instantiate a malicious ActiveX control, fetch a CAB archive, and extract a disguised DLL outside the intended path for Control Panel loading. The victim must open the document; payload code runs with that user's rights, and targeted attacks have used the chain.

CVSS severity7.8
High
EPSS probability97.45%
Next 30 days · Sep 16, 2026
Known exploitationReported
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Remote code execution in MSHTML in Microsoft Windows allows remote attackers to run code through a crafted Office document. A crafted document makes the browser rendering engine instantiate a malicious ActiveX control, fetch a CAB archive, and extract a disguised DLL outside the intended path for Control Panel loading. The victim must open the document; payload code runs with that user's rights, and targeted attacks have used the chain.

The record

CVE
CVE-2021-40444
Published
Sep 15, 2021
Updated
Aug 10, 2026
Vendor
Microsoft
Product
Windows 10 Version 1507
Classifications
CWE-22, T1204.002, T1203
Attack vector
local
Privileges
unauthenticated

Timeline

How it unfolded

  1. Sep 15, 2021CVE publishedPublication date reported by the CVE source.
  2. Nov 3, 2021Exploitation reportedMicrosoft MSHTML Remote Code Execution Vulnerability
  3. Aug 10, 2026Record 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=10.0.10240.0 <10.0.10240.19060

What conditions does exploitation require?

Attack vectorlocal
Required privilegesunauthenticated

What is affected?

Microsoft · Windows 10 Version 1507version=10.0.10240.0 <10.0.10240.19060
Microsoft · Windows Server 2019version=10.0.17763.0 <10.0.17763.2183
Microsoft · Windows 7version=6.1.0 <6.1.7601.25712
Microsoft · Windows 10 Version 21H1version=10.0.0 <10.0.19043.1237
Microsoft · Windows 10 Version 1909version=10.0.0 <10.0.18363.1801
Microsoft · Windows 8.1version=6.3.0 <6.3.9600.20120
Microsoft · Windows Server 2016 (Server Core installation)version=10.0.14393.0 <10.0.14393.4651
Microsoft · Windows Server 2012 (Server Core installation)version=6.2.9200.0 <6.2.9200.23462
Microsoft · Windows Server 2012version=6.2.9200.0 <6.2.9200.23462
Microsoft · Windows Server, version 2004version=10.0.0 <10.0.19041.1237
Microsoft · Windows Server 2016version=10.0.14393.0 <10.0.14393.4651
Microsoft · Windows Server 2008 R2 Service Pack 1version=6.1.7601.0 <6.1.7601.25712
Microsoft · Windows 10 Version 20H2version=10.0.0 <10.0.19042.1237
Microsoft · Windows Server 2008 R2 Service Pack 1 (Server Core installation)version=6.1.7601.0 <6.1.7601.25712
Microsoft · Windows Server 2012 R2 (Server Core installation)version=6.3.9600.0 <6.3.9600.20120
Microsoft · Windows Server 2019 (Server Core installation)version=10.0.17763.0 <10.0.17763.2183
Microsoft · Windows 7 Service Pack 1version=6.1.0 <6.1.7601.25712
Microsoft · Windows Server version 20H2version=10.0.0 <10.0.19042.1237
Microsoft · Windows 10 Version 1607version=10.0.14393.0 <10.0.14393.4651
Microsoft · Windows Server 2008 Service Pack 2version=6.0.6003.0 <6.0.6003.21218
Microsoft · Windows Server 2022version=10.0.20348.0 <10.0.20348.230
Microsoft · Windows 10 Version 2004version=10.0.0 <10.0.19041.1237
Microsoft · Windows 10 Version 1809version=10.0.0 <10.0.17763.2183; version=10.0.17763.0 <10.0.17763.2183
Microsoft · Windows Server 2012 R2version=6.3.9600.0 <6.3.9600.20120
Microsoft · Windows Server 2008 Service Pack 2 (Server Core installation)version=6.0.6003.0 <6.0.6003.21218

Published CVSS scores

7.8National Vulnerability DatabaseCVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/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.

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No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectorlocal
Privilegesunauthenticated
Known exploitationReported
Public exploitPublished

Weakness, pattern, technique

CWE-22Improper Limitation of a Pathname to a Restricted Directory ('Path Traversal')
T1204.002User Execution: Malicious File
T1203Exploitation for Client Execution

Public exploit references

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

Reported exploitation

Technologies

Your stack

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Your stack

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