Reference page — cumulative record through Wednesday, August 19, 2026 UTC. Reference pages update as the archive grows; only dated daily editions are immutable pages of record.
Microsoft MSHTML Remote Code Execution Vulnerability
AV AC PR UI S C I A CVSS EPSS %ile KEV
N L N R C L H L 8.8 .9745 99.9 YES
AFFECTED
Product Versions Fixed
Windows 10 Version 1507 10.0.10240.0 – —
Windows 10 Version 1607 10.0.14393.0 – —
Windows 10 Version 1809 10.0.17763.0 – —
Windows 10 Version 1809 10.0.0 – —
Windows 10 Version 1909 10.0.0 – —
Windows 10 Version 2004 10.0.0 – —
Windows 10 Version 20H2 10.0.0 – —
Windows 10 Version 21H1 10.0.0 – —
Windows 7 6.1.0 – —
Windows 7 Service Pack 1 6.1.0 – —
+ 16 more
TIMELINE
Sep 2 Reserved by microsoft
Nov 3 Added to CISA KEV, remediation due 2021-11-17
Nov 3 Published (CNA: microsoft)
Aug 10 EXPLOIT PUBLISHED — CVE-2021-40444 (Microsoft Windows 10 Version 1507). Public exploit reference added.
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.
Lifecycle
Complete event history — 4 events, chronological
| Date | Event | Detail |
|---|
| September 2, 2021 | Reserved | Reserved by microsoft |
| November 3, 2021 | KEV ADDED | Added to CISA KEV, remediation due 2021-11-17 |
| November 3, 2021 | Published | Published (CNA: microsoft) |
| August 10, 2026 | EXPLOIT PUBLISHED | EXPLOIT PUBLISHED — CVE-2021-40444 (Microsoft Windows 10 Version 1507). Public exploit reference added. |
Affected
Affected products and packages — 26 rows
| Vendor | Product / Package | Ecosystem | Version introduced | Fixed |
|---|
| Microsoft | Windows 10 Version 1507 | — | 10.0.10240.0 | — |
| Microsoft | Windows 10 Version 1607 | — | 10.0.14393.0 | — |
| Microsoft | Windows 10 Version 1809 | — | 10.0.17763.0 | — |
| Microsoft | Windows 10 Version 1809 | — | 10.0.0 | — |
| Microsoft | Windows 10 Version 1909 | — | 10.0.0 | — |
| Microsoft | Windows 10 Version 2004 | — | 10.0.0 | — |
| Microsoft | Windows 10 Version 20H2 | — | 10.0.0 | — |
| Microsoft | Windows 10 Version 21H1 | — | 10.0.0 | — |
| Microsoft | Windows 7 | — | 6.1.0 | — |
| Microsoft | Windows 7 Service Pack 1 | — | 6.1.0 | — |
| Microsoft | Windows 8.1 | — | 6.3.0 | — |
| Microsoft | Windows Server 2008 R2 Service Pack 1 | — | 6.1.7601.0 | — |
| Microsoft | Windows Server 2008 R2 Service Pack 1 (Server Core installation) | — | 6.1.7601.0 | — |
| Microsoft | Windows Server 2008 Service Pack 2 | — | 6.0.6003.0 | — |
| Microsoft | Windows Server 2008 Service Pack 2 (Server Core installation) | — | 6.0.6003.0 | — |
| Microsoft | Windows Server 2012 | — | 6.2.9200.0 | — |
| Microsoft | Windows Server 2012 (Server Core installation) | — | 6.2.9200.0 | — |
| Microsoft | Windows Server 2012 R2 | — | 6.3.9600.0 | — |
| Microsoft | Windows Server 2012 R2 (Server Core installation) | — | 6.3.9600.0 | — |
| Microsoft | Windows Server 2016 | — | 10.0.14393.0 | — |
| Microsoft | Windows Server 2016 (Server Core installation) | — | 10.0.14393.0 | — |
| Microsoft | Windows Server 2019 | — | 10.0.17763.0 | — |
| Microsoft | Windows Server 2019 (Server Core installation) | — | 10.0.17763.0 | — |
| Microsoft | Windows Server 2022 | — | 10.0.20348.0 | — |
| Microsoft | Windows Server version 2004 | — | 10.0.0 | — |
| Microsoft | Windows Server version 20H2 | — | 10.0.0 | — |
About this page
This is a reference page, not a dated page of record. It assembles the complete lifecycle of CVE-2021-40444 from the CVE Program record, NVD enrichment, the CISA KEV catalog, EPSS, and OSV advisories. The box score's numbers (CVSS, EPSS, KEV status) are current as of Wednesday, August 19, 2026 UTC and are re-derived as the archive grows; only dated daily editions are immutable pages of record. The authoritative source for this identifier is cve.org.