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CVE-2021-40444

Microsoft MSHTML Remote Code Execution Vulnerability

Affects many Windows versions, from Windows 7 and 8.1 to Windows 10 and Server 2008 through 2022, when an attacker-crafted ActiveX control is used by a Microsoft Office document. Fixed in the listed builds.

Published
Last modified
published
Listed in CISA KEV
Actively exploited
Fix
Fixed in 10.0.10240.19060, 10.0.14393.4651, 10.0.17763.2183, 10.0.18363.1801, 10.0.19041.1237, and 7 more
1 Metasploit module, 35 proofs of concept on GitHub
  • Exploitation: active
  • Automatable: no
  • Technical impact: total

Summary

This vulnerability affects Microsoft Windows systems through the MSHTML browser rendering engine, which can be reached through Microsoft Office documents. An attacker who gets a user to open a specially crafted document could execute code on the affected system, with greater impact on accounts that have administrative rights.

Summarized by anthropic/claude-haiku-5.5. Verify details against the original sources.

Read the original 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.

Timeline

  1. CISA SSVC assessment

    Exploitation: active · Automatable: no · Technical impact: total

  2. CVE published
  3. Added to CISA KEV

    CISA has evidence of exploitation in the wild

  4. CISA remediation deadline

    Due date for US federal agencies to patch

  5. Record last updated
  6. EPSS reached 10%

    FIRST estimates at least a 10% chance of exploitation in the next 30 days

Affected versions

  • Microsoft Windows 10 Version 1507

    From 10.0.10240.0 · fixed in 10.0.10240.19060

  • Microsoft Windows 10 Version 1607

    From 10.0.14393.0 · fixed in 10.0.14393.4651

  • Microsoft Windows 10 Version 1809

    From 10.0.17763.0 · fixed in 10.0.17763.2183

  • Microsoft Windows 10 Version 1809

    From 10.0.0 · fixed in 10.0.17763.2183

  • Microsoft Windows 10 Version 1909

    From 10.0.0 · fixed in 10.0.18363.1801

  • Microsoft Windows 10 Version 2004

    From 10.0.0 · fixed in 10.0.19041.1237

  • Microsoft Windows 10 Version 20H2

    From 10.0.0 · fixed in 10.0.19042.1237

  • Microsoft Windows 10 Version 21H1

    From 10.0.0 · fixed in 10.0.19043.1237

  • Microsoft Windows 7

    From 6.1.0 · fixed in 6.1.7601.25712

  • Microsoft Windows 7 Service Pack 1

    From 6.1.0 · fixed in 6.1.7601.25712

  • Microsoft Windows 8.1

    From 6.3.0 · fixed in 6.3.9600.20120

  • Microsoft Windows Server 2008 R2 Service Pack 1

    From 6.1.7601.0 · fixed in 6.1.7601.25712

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

    From 6.1.7601.0 · fixed in 6.1.7601.25712

  • Microsoft Windows Server 2008 Service Pack 2

    From 6.0.6003.0 · fixed in 6.0.6003.21218

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

    From 6.0.6003.0 · fixed in 6.0.6003.21218

  • Microsoft Windows Server 2012

    From 6.2.9200.0 · fixed in 6.2.9200.23462

  • Microsoft Windows Server 2012 (Server Core installation)

    From 6.2.9200.0 · fixed in 6.2.9200.23462

  • Microsoft Windows Server 2012 R2

    From 6.3.9600.0 · fixed in 6.3.9600.20120

  • Microsoft Windows Server 2012 R2 (Server Core installation)

    From 6.3.9600.0 · fixed in 6.3.9600.20120

  • Microsoft Windows Server 2016

    From 10.0.14393.0 · fixed in 10.0.14393.4651

  • Microsoft Windows Server 2016 (Server Core installation)

    From 10.0.14393.0 · fixed in 10.0.14393.4651

  • Microsoft Windows Server 2019

    From 10.0.17763.0 · fixed in 10.0.17763.2183

  • Microsoft Windows Server 2019 (Server Core installation)

    From 10.0.17763.0 · fixed in 10.0.17763.2183

  • Microsoft Windows Server 2022

    From 10.0.20348.0 · fixed in 10.0.20348.230

  • Microsoft Windows Server version 2004

    From 10.0.0 · fixed in 10.0.19041.1237

  • Microsoft Windows Server version 20H2

    From 10.0.0 · fixed in 10.0.19042.1237

References 37

msrc.microsoft.com

GitHub · rapid7/metasploit-framework

GitHub · 34zY/Microsoft-Office-Word-MSHTML-Remote-Code-Execution-Exploit

GitHub · Alexcot25051999/CVE-2021-40444

GitHub · DarkSprings/CVE-2021-40444

GitHub · Edubr2020/CVE-2021-40444--CABless

GitHub · H0j3n/CVE-2021-40444

GitHub · Immersive-Labs-Sec/cve-2021-40444-analysis

GitHub · Jeromeyoung/MSHTMHell

GitHub · Jeromeyoung/TIC4301_Project

GitHub · KnoooW/CVE-2021-40444-docx-Generate

GitHub · LazarusReborn/Docx-Exploit-2021

GitHub · MRacumen/CVE-2021-40444

GitHub · W1kyri3/Exploit-PoC-CVE-2021-40444-inject-ma-doc-vao-docx

GitHub · Zeop-CyberSec/word_mshtml

GitHub · aslitsecurity/CVE-2021-40444_builders

GitHub · bambooqj/CVE-2021-40444_EXP_JS

GitHub · basim-ahmad/Follina-CVE-and-CVE-2021-40444

GitHub · fengjixuchui/CVE-2021-40444-docx-Generate

GitHub · hqdat809/CVE-2021-40444

GitHub · jamesrep/cve-2021-40444

GitHub · k4k4/CVE-2021-40444-Sample

GitHub · k8gege/CVE-2021-40444

GitHub · kagura-maru/CVE-2021-40444-POC

GitHub · kal1gh0st/CVE-2021-40444_CAB_archives

GitHub · klezVirus/CVE-2021-40444

GitHub · lisinan988/CVE-2021-40444-exp

GitHub · lockedbyte/CVE-2021-40444

GitHub · m4madturk/CVE-2021-40444

GitHub · mansk1es/Caboom

GitHub · metehangenel/MSHTML-CVE-2021-40444

GitHub · nvchungkma/CVE-2021-40444-Microsoft-Office-Word-Remote-Code-Execution-

GitHub · ozergoker/CVE-2021-40444

GitHub · rankthree/SOC-Detection-T1003.001-CVE-2021-40444

GitHub · rfcxv/CVE-2021-40444-POC

GitHub · tiagob0b/CVE-2021-40444

GitHub · vysecurity/CVE-2021-40444

FAQ

Questions about CVE-2021-40444

What does this mean?

An attacker can craft a malicious ActiveX control for a Microsoft Office document that hosts the browser rendering engine (MSHTML), which can lead to remote code execution. The flaw is in how Windows handles that control.Source: github.com

Am I affected, and how do I check?

The advisory lists Windows 7, 8.1, 10 (versions 1507 to 21H1), and Windows Server 2008 SP2 through Server 2022, including Server Core installations and Windows Server version 2004 and 20H2. To check a system, compare its build number (shown by the winver command) with the fixed build listed for its product.Source: github.com

What should I do about it?

Install the Microsoft security update for CVE-2021-40444 so the system reaches the fixed build listed for its product, such as 10.0.19041.1237 for Windows 10 version 2004.Source: github.com

Is it being exploited?

Yes. CISA added it to its Known Exploited Vulnerabilities catalog on 2021-11-03, which means it has evidence of attacks. Public exploit code exists (Metasploit, a proof of concept on GitHub).Source: cisa.gov, cve.now feed data