CVE-2021-40444
Microsoft MSHTML Remote Code Execution Vulnerability
Published Sep 15, 2021 · updated Aug 10, 2026 · microsoft windows 10 1507
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
Detection, updates, and resolution for this record.
Sep 15, 2021 · Catalog
Detected
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 attack
Nov 3, 2021 · CISA KEV
Known exploited
Apply updates per vendor instructions.
Nov 17, 2021 · CISA KEV
Remediation due
Apply updates per vendor instructions.
Aug 10, 2026 · Catalog
Updated
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 attack
Required action
Apply updates per vendor instructions.
CISA due date Nov 17, 2021
Affected
- cpe microsoft/windows 10 1507version unspecified
- cpe microsoft/windows 10 1607version unspecified
- cpe microsoft/windows 10 1809version unspecified
- cpe microsoft/windows 10 1909version unspecified
- cpe microsoft/windows 10 2004version unspecified
- cpe microsoft/windows 10 20h2version unspecified
- cpe microsoft/windows 10 21h1version unspecified
- cpe microsoft/windows 7version unspecified
- vendor Microsoft MSHTMLversion unspecified
Sources
- CISA KEVCVE-2021-40444
Microsoft MSHTML contains a unspecified vulnerability that allows for remote code execution.
cisa.gov - CVE.orgCVE-2021-40444
Official CVE identifier
cve.org - FIRST EPSSCVE-2021-40444
30-day exploitation probability 97.5%
first.org - Metasploit Modulesexploit_windows/fileformat/word_mshtml_rce
Public module reference (excellent). Module source is not copied into this catalog.
rapid7.com - NIST NVDCVE-2021-40444
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
nvd.nist.gov - Packet Storm Securityhttp://packetstormsecurity.com/files/164210/Microsoft-Windows-MSHTML-Overview.html
Packet Storm link already published on the finding.
packetstormsecurity.com - Packet Storm Securityhttp://packetstormsecurity.com/files/165214/Microsoft-Office-Word-MSHTML-Remote-Code-Execution.html
Packet Storm link already published on the finding.
packetstormsecurity.com - Packet Storm Securityhttp://packetstormsecurity.com/files/167317/Microsoft-Office-MSDT-Follina-Proof-Of-Concept.html
Packet Storm link already published on the finding.
packetstormsecurity.com