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CVE-2021-40444

Microsoft MSHTML Remote Code Execution Vulnerability

CVSS 3.1 High 8.8Known exploited (CISA KEV)

CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:H/A:L/E:P/RL:O/RC:C

Description

Microsoft is investigating reports of a remote code execution vulnerability in MSHTML that affects Microsoft Windows. Microsoft is aware of targeted attacks that attempt to exploit this vulnerability by using specially-crafted Microsoft Office documents. An attacker could craft a malicious ActiveX control to be used by a Microsoft Office document that hosts the browser rendering engine. The attacker would then have to convince the user to open the malicious document. Users whose accounts are configured to have fewer user rights on the system could be less impacted than users who operate with administrative user rights. Microsoft Defender Antivirus and Microsoft Defender for Endpoint both provide detection and protections for the known vulnerability. Customers should keep antimalware products up to date. Customers who utilize automatic updates do not need to take additional action. Enterprise customers who manage updates should select the detection build 1.349.22.0 or newer and deploy it across their environments. Microsoft Defender for Endpoint alerts will be displayed as: “Suspicious Cpl File Execution”. Upon completion of this investigation, Microsoft will take the appropriate action to help protect our customers. This may include providing a security update through our monthly release process or providing an out-of-cycle security update, depending on customer needs. Please see the Mitigations and Workaround sections for important information about steps you can take to protect your system from this vulnerability. UPDATE September 14, 2021: Microsoft has released security updates to address this vulnerability. Please see the Security Updates table for the applicable update for your system. We recommend that you install these updates immediately. Please see the FAQ for important information about which updates are applicable to your system.

Official description from the CVE record, published by microsoft. Copyright © 1999-2026 The MITRE Corporation. See /security/cve/legal for the CVE license. View the record on cve.org

Key data

CVSS 3.1 High 8.8

Score published by microsoft in the CVE record.

CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:H/A:L/E:P/RL:O/RC:C

  • Attack vector: Network

    The vulnerable component can be reached over a network, possibly from the Internet.

  • Attack complexity: Low

    No special conditions are needed. The attack can be repeated at will.

  • Privileges required: None

    No account or privileges are needed.

  • User interaction: Required

    A user has to do something first, such as opening a file or following a link.

  • Scope: Changed

    The impact can reach other components beyond the vulnerable one.

  • Confidentiality impact: Low

    Limited effect on the secrecy of data.

  • Integrity impact: High

    Serious or total effect on the trustworthiness of data.

  • Availability impact: Low

    Limited effect on availability.

CVSS is owned and managed by FIRST.Org, Inc. (FIRST) and is used by permission. Each CVSS score on this site is shown together with its vector string, as published in the CVE record by the source named next to it. Learn more at first.org/cvss.

EPSS

Exploit Prediction Scoring System by FIRST: an estimate of the probability that exploitation activity will be observed in the next 30 days.
Score
0.97840 (97.8% probability)
Percentile
99.9%
Scores of
Nov 10, 2026
Model
v2026.06.15

CISA Known Exploited Vulnerabilities

This CVE is listed in the CISA KEV catalog.
Name in the catalog
Microsoft MSHTML Remote Code Execution Vulnerability
Added to the catalog
Nov 3, 2021
Federal due date
Nov 17, 2021
Ransomware campaigns
Known use

CISA assessment as of Sep 8, 2021

Stakeholder-Specific Vulnerability Categorization (SSVC) decision points added by CISA.
Exploitation
Recorded by CISA as active
Automatable
no
Technical impact
total

Weakness (CWE)

CWE catalog version 5.0.
CWE names: Copyright © 2006-2026, The MITRE Corporation. See /security/cve/legal for the CWE license.
  • CWE-22Improper Limitation of a Pathname to a Restricted Directory

Affected products

Products listed in the CVE record, as the CNA published them.

  • Microsoft Windows 10 Version 1507

    • affected: 10.0.10240.0 up to before 10.0.10240.19060

  • Microsoft Windows 10 Version 1607

    • affected: 10.0.14393.0 up to before 10.0.14393.4651

  • Microsoft Windows 10 Version 1809

    • affected: 10.0.17763.0 up to before 10.0.17763.2183

  • Microsoft Windows 10 Version 1809

    • affected: 10.0.0 up to before 10.0.17763.2183

  • Microsoft Windows 10 Version 1909

    • affected: 10.0.0 up to before 10.0.18363.1801

  • Microsoft Windows 10 Version 2004

    • affected: 10.0.0 up to before 10.0.19041.1237

  • Microsoft Windows 10 Version 20H2

    • affected: 10.0.0 up to before 10.0.19042.1237

  • Microsoft Windows 10 Version 21H1

    • affected: 10.0.0 up to before 10.0.19043.1237

  • Microsoft Windows 7

    • affected: 6.1.0 up to before 6.1.7601.25712

  • Microsoft Windows 7 Service Pack 1

    • affected: 6.1.0 up to before 6.1.7601.25712

  • Microsoft Windows 8.1

    • affected: 6.3.0 up to before 6.3.9600.20120

  • Microsoft Windows Server 2008 R2 Service Pack 1

    • affected: 6.1.7601.0 up to before 6.1.7601.25712

  • Microsoft Windows Server 2008 R2 Service Pack 1 (Server Core installation)

    • affected: 6.1.7601.0 up to before 6.1.7601.25712

  • Microsoft Windows Server 2008 Service Pack 2

    • affected: 6.0.6003.0 up to before 6.0.6003.21218

  • Microsoft Windows Server 2008 Service Pack 2 (Server Core installation)

    • affected: 6.0.6003.0 up to before 6.0.6003.21218

  • Microsoft Windows Server 2012

    • affected: 6.2.9200.0 up to before 6.2.9200.23462

  • Microsoft Windows Server 2012 (Server Core installation)

    • affected: 6.2.9200.0 up to before 6.2.9200.23462

  • Microsoft Windows Server 2012 R2

    • affected: 6.3.9600.0 up to before 6.3.9600.20120

  • Microsoft Windows Server 2012 R2 (Server Core installation)

    • affected: 6.3.9600.0 up to before 6.3.9600.20120

  • Microsoft Windows Server 2016

    • affected: 10.0.14393.0 up to before 10.0.14393.4651

  • Microsoft Windows Server 2016 (Server Core installation)

    • affected: 10.0.14393.0 up to before 10.0.14393.4651

  • Microsoft Windows Server 2019

    • affected: 10.0.17763.0 up to before 10.0.17763.2183

  • Microsoft Windows Server 2019 (Server Core installation)

    • affected: 10.0.17763.0 up to before 10.0.17763.2183

  • Microsoft Windows Server 2022

    • affected: 10.0.20348.0 up to before 10.0.20348.230

  • Microsoft Windows Server version 2004

    • affected: 10.0.0 up to before 10.0.19041.1237

  • Microsoft Windows Server version 20H2

    • affected: 10.0.0 up to before 10.0.19042.1237

References

Links listed in the CVE record. They lead to other sites, which CubePath does not control.

Timeline

  1. ID reserved
  2. Record published
  3. Added to CISA KEV
  4. Record last updated

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Data from the CVE Program (MITRE), CISA KEV and FIRST EPSS. CVSS is owned by FIRST and used by permission. Not affiliated with or endorsed by MITRE, CISA or FIRST. Data as of Nov 10, 2026, 19:38 UTC. Sources and licenses