CVE-2021-40444: Microsoft MSHTML Remote Code Execution Vulnerability
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.
Other sources
Microsoft MSHTML contains a unspecified vulnerability that allows for remote code execution.
— CISA
Microsoft MSHTML Remote Code Execution Vulnerability
Affected Software
Remediation
Recommended actions to resolve this vulnerability, in priority order.
- Upgrade
Upgrade to a fixed release to a version that resolves this vulnerability.
Fixed in 6.1.7601.25712Fixed in 1.001Fixed in 6.1.7601.26221Patch KB5019958 - Upgrade
Upgrade to a fixed release to a version that resolves this vulnerability.
Fixed in 6.1.7601.25712Fixed in 1.001Patch KB5005563 - Upgrade
Upgrade to a fixed release to a version that resolves this vulnerability.
Fixed in 6.0.6003.21218Fixed in 1.001Patch KB5005563 - Upgrade
Upgrade to a fixed release to a version that resolves this vulnerability.
Fixed in 6.3.9600.20120Fixed in 1.001Patch KB5005563 - Upgrade
Upgrade to a fixed release to a version that resolves this vulnerability.
Fixed in 6.2.9200.23462Fixed in 1.001Patch KB5005563 - Upgrade
Upgrade to a fixed release to a version that resolves this vulnerability.
Fixed in 10.0.14393.4651Patch KB5005573 - Upgrade
Upgrade to a fixed release to a version that resolves this vulnerability.
Fixed in 6.3.9600.20120Patch KB5005613 - Upgrade
Upgrade to a fixed release to a version that resolves this vulnerability.
Fixed in 10.0.10240.19060Patch KB5005569 - Upgrade
Upgrade to a fixed release to a version that resolves this vulnerability.
Fixed in 10.0.19042.1237Patch KB5005565 - Upgrade
Upgrade to a fixed release to a version that resolves this vulnerability.
Fixed in 10.0.19041.1237Patch KB5005565 - Upgrade
Upgrade to a fixed release to a version that resolves this vulnerability.
Fixed in 10.0.20348.230Patch KB5005575 - Upgrade
Upgrade to a fixed release to a version that resolves this vulnerability.
Fixed in 10.0.19043.1237Patch KB5005565 - Upgrade
Upgrade to a fixed release to a version that resolves this vulnerability.
Fixed in 10.0.18363.1801Patch KB5005566 - Upgrade
Upgrade to a fixed release to a version that resolves this vulnerability.
Fixed in 10.0.17763.2183Patch KB5005568 - Upgrade
Upgrade to a fixed release to a version that resolves this vulnerability.
Patch detection build 1.349.22.0 or newer - Configuration
Reduce user privileges (run Office/MSHTML-related tasks with fewer user rights rather than administrative rights) to lessen impact.
User account permissions operating with fewer user rights vs administrative user rights = fewer user rights - Compensating control
Ensure Microsoft Defender Antivirus and Microsoft Defender for Endpoint are deployed/enabled for detection and protections; review for alerts displayed as “Suspicious Cpl File Execution”.
- Operational
Keep antimalware products up to date; for enterprise update management, select the detection build 1.349.22.0 or newer and deploy across environments.
Event History
Frequently Asked Questions
What is CVE-2021-40444?
CVE-2021-40444 is a Microsoft MSHTML Remote Code Execution Vulnerability.
What is the severity of CVE-2021-40444?
The severity of CVE-2021-40444 is high with a CVSS score of 7.8.
Which software is affected by CVE-2021-40444?
Microsoft MSHTML and various versions of Microsoft Windows 10, Windows 7, Windows 8.1, Windows RT 8.1, Windows Server 2008, Windows Server 2012, Windows Server 2016, Windows Server 2019, and Windows Server 2022 are affected by CVE-2021-40444.
How can I fix CVE-2021-40444?
Apply the security updates provided by Microsoft to fix CVE-2021-40444.
Where can I find more information about CVE-2021-40444?
You can find more information about CVE-2021-40444 at the following references: http://packetstormsecurity.com/files/164210/Microsoft-Windows-MSHTML-Overview.html, http://packetstormsecurity.com/files/165214/Microsoft-Office-Word-MSHTML-Remote-Code-Execution.html, http://packetstormsecurity.com/files/167317/Microsoft-Office-MSDT-Follina-Proof-Of-Concept.html