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CVE-2021-40444

HIGH · CVSS 8.8 · Analyzed

Published: 2021-09-15 · Updated: 2026-08-10 · Source: NVD

Vulnerability overview

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.

Severity and scoring

CVSS score
8.8 · HIGH
CVSS version
3.1
CVSS vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:H/A:L
Weaknesses
CWE-22

CVSS measures technical severity; it does not establish whether this vulnerability is being exploited in your environment.

Known exploitation and remediation

Listed in CISA’s Known Exploited Vulnerabilities catalog.

Affected product
Microsoft · MSHTML
Added to catalog
2021-11-03
Required action
Apply updates per vendor instructions.
CISA remediation due date
2021-11-17

CISA deadlines apply to the organizations covered by its directives. Confirm your own remediation requirements.

Verify affected versions and patch availability in the vendor advisory before making changes.

Affected products and versions

  • cpe:2.3:o:microsoft:windows_10_1507:*:*:*:*:*:*:*:*

    Before (exclusive): 10.0.10240.19060

  • cpe:2.3:o:microsoft:windows_10_1607:*:*:*:*:*:*:*:*

    Before (exclusive): 10.0.14393.4651

  • cpe:2.3:o:microsoft:windows_10_1809:*:*:*:*:*:*:*:*

    Before (exclusive): 10.0.17763.2183

  • cpe:2.3:o:microsoft:windows_10_1909:*:*:*:*:*:*:*:*

    Before (exclusive): 10.0.18363.1801

  • cpe:2.3:o:microsoft:windows_10_2004:*:*:*:*:*:*:*:*

    Before (exclusive): 10.0.19041.1237

  • cpe:2.3:o:microsoft:windows_10_20h2:*:*:*:*:*:*:*:*

    Before (exclusive): 10.0.19042.1237

  • cpe:2.3:o:microsoft:windows_10_21h1:*:*:*:*:*:*:*:*

    Before (exclusive): 10.0.19043.1237

  • cpe:2.3:o:microsoft:windows_7:-:sp1:*:*:*:*:*:*

  • cpe:2.3:o:microsoft:windows_8.1:-:*:*:*:*:*:*:*

  • cpe:2.3:o:microsoft:windows_rt_8.1:-:*:*:*:*:*:*:*

  • cpe:2.3:o:microsoft:windows_server_2004:*:*:*:*:*:*:*:*

    Before (exclusive): 10.0.19041.1237

  • cpe:2.3:o:microsoft:windows_server_2008:-:sp2:*:*:*:*:*:*

  • cpe:2.3:o:microsoft:windows_server_2008:r2:sp1:*:*:*:*:x64:*

  • cpe:2.3:o:microsoft:windows_server_2012:-:*:*:*:*:*:*:*

  • cpe:2.3:o:microsoft:windows_server_2012:-:r2:*:*:*:*:*:*

  • cpe:2.3:o:microsoft:windows_server_2016:*:*:*:*:*:*:*:*

    Before (exclusive): 10.0.14393.4651

  • cpe:2.3:o:microsoft:windows_server_2019:*:*:*:*:*:*:*:*

    Before (exclusive): 10.0.17763.2183

  • cpe:2.3:o:microsoft:windows_server_2022:*:*:*:*:*:*:*:*

    Before (exclusive): 10.0.20348.230

  • cpe:2.3:o:microsoft:windows_server_20h2:*:*:*:*:*:*:*:*

    Before (exclusive): 10.0.19042.1237

These are NVD CPE applicability entries. Some products depend on configuration conditions; consult the official record to confirm applicability.

Advisories and references

Explore official sources

Read the official NVD record ↗

Explore the CISA catalog ↗

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