Microsoft MSHTML Remote Code Execution Vulnerability

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Summary

CVECVE-2021-40444
StatePUBLISHED
Assignermicrosoft
Source PriorityCVE Program / NVD first with legacy fallback
Published2021-09-15 12:15:16 UTC
Updated2026-08-10 20:19:30 UTC
DescriptionMicrosoft 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.

Risk And Classification

Primary CVSS: v3.1 7.8 HIGH from [email protected]

CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H

EPSS: 0.974500000 probability, percentile 0.998950000 (date 2026-08-15)

CISA KEV: Listed on 2021-11-03; due 2021-11-17; ransomware use Known

Problem Types: CWE-22 | Remote Code Execution | CWE-22 CWE-22 Improper Limitation of a Pathname to a Restricted Directory ('Path Traversal')

VersionSourceTypeScoreSeverityVector
3.1[email protected]Secondary7.8HIGHCVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H
3.1[email protected]Secondary8.8HIGHCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:H/A:L
3.1CNACVSS8.8HIGHCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:H/A:L/E:P/RL:O/RC:C
2.0[email protected]Primary6.8AV:N/AC:M/Au:N/C:P/I:P/A:P

CVSS v3.1 Breakdown

Attack Vector
Local
Attack Complexity
Low
Privileges Required
None
User Interaction
Required
Scope
Unchanged
Confidentiality
High
Integrity
High
Availability
High

CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H

CVSS v2.0 Breakdown

Access Vector
Network
Access Complexity
Medium
Authentication
None
Confidentiality
Partial
Integrity
Partial
Availability
Partial

AV:N/AC:M/Au:N/C:P/I:P/A:P

CISA Known Exploited Vulnerability

VendorMicrosoft
ProductMSHTML
NameMicrosoft MSHTML Remote Code Execution Vulnerability
Required ActionApply updates per vendor instructions.
Noteshttps://nvd.nist.gov/vuln/detail/CVE-2021-40444

NVD Known Affected Configurations (CPE 2.3)

TypeVendorProductVersionUpdateEditionLanguage
Operating System Microsoft Windows 10 1507 All All All All
Operating System Microsoft Windows 10 1607 All All All All
Operating System Microsoft Windows 10 1809 All All All All
Operating System Microsoft Windows 10 1909 All All All All
Operating System Microsoft Windows 10 2004 All All All All
Operating System Microsoft Windows 10 20h2 All All All All
Operating System Microsoft Windows 10 21h1 All All All All
Operating System Microsoft Windows 7 - sp1 All All
Operating System Microsoft Windows 8.1 - All All All
Operating System Microsoft Windows Rt 8.1 - All All All
Operating System Microsoft Windows Server 2004 All All All All
Operating System Microsoft Windows Server 2008 - sp2 All All
Operating System Microsoft Windows Server 2008 r2 sp1 All All
Operating System Microsoft Windows Server 2012 - All All All
Operating System Microsoft Windows Server 2012 - r2 All All
Operating System Microsoft Windows Server 2016 All All All All
Operating System Microsoft Windows Server 2019 All All All All
Operating System Microsoft Windows Server 2022 All All All All
Operating System Microsoft Windows Server 20h2 All All All All

Vendor Declared Affected Products

SourceVendorProductVersionPlatforms
CNA Microsoft Windows 10 Version 1507 affected 10.0.10240.0 10.0.10240.19060 custom 32-bit Systems, x64-based Systems
CNA Microsoft Windows 10 Version 1607 affected 10.0.14393.0 10.0.14393.4651 custom 32-bit Systems, x64-based Systems
CNA Microsoft Windows 10 Version 1809 affected 10.0.17763.0 10.0.17763.2183 custom 32-bit Systems, x64-based Systems
CNA Microsoft Windows 10 Version 1809 affected 10.0.0 10.0.17763.2183 custom ARM64-based Systems
CNA Microsoft Windows 10 Version 1909 affected 10.0.0 10.0.18363.1801 custom 32-bit Systems, ARM64-based Systems, x64-based Systems
CNA Microsoft Windows 10 Version 2004 affected 10.0.0 10.0.19041.1237 custom 32-bit Systems, ARM64-based Systems, x64-based Systems
CNA Microsoft Windows 10 Version 20H2 affected 10.0.0 10.0.19042.1237 custom 32-bit Systems, ARM64-based Systems
CNA Microsoft Windows 10 Version 21H1 affected 10.0.0 10.0.19043.1237 custom 32-bit Systems, ARM64-based Systems, x64-based Systems
CNA Microsoft Windows 7 affected 6.1.0 6.1.7601.25712 custom 32-bit Systems
CNA Microsoft Windows 7 Service Pack 1 affected 6.1.0 6.1.7601.25712 custom x64-based Systems
CNA Microsoft Windows 8.1 affected 6.3.0 6.3.9600.20120 custom 32-bit Systems, ARM64-based Systems, x64-based Systems
CNA Microsoft Windows Server 2008 R2 Service Pack 1 affected 6.1.7601.0 6.1.7601.25712 custom x64-based Systems
CNA Microsoft Windows Server 2008 R2 Service Pack 1 Server Core Installation affected 6.1.7601.0 6.1.7601.25712 custom x64-based Systems
CNA Microsoft Windows Server 2008 Service Pack 2 affected 6.0.6003.0 6.0.6003.21218 custom 32-bit Systems, x64-based Systems
CNA Microsoft Windows Server 2008 Service Pack 2 Server Core Installation affected 6.0.6003.0 6.0.6003.21218 custom 32-bit Systems, x64-based Systems
CNA Microsoft Windows Server 2012 affected 6.2.9200.0 6.2.9200.23462 custom x64-based Systems
CNA Microsoft Windows Server 2012 Server Core Installation affected 6.2.9200.0 6.2.9200.23462 custom x64-based Systems
CNA Microsoft Windows Server 2012 R2 affected 6.3.9600.0 6.3.9600.20120 custom x64-based Systems
CNA Microsoft Windows Server 2012 R2 Server Core Installation affected 6.3.9600.0 6.3.9600.20120 custom x64-based Systems
CNA Microsoft Windows Server 2016 affected 10.0.14393.0 10.0.14393.4651 custom x64-based Systems
CNA Microsoft Windows Server 2016 Server Core Installation affected 10.0.14393.0 10.0.14393.4651 custom x64-based Systems
CNA Microsoft Windows Server 2019 affected 10.0.17763.0 10.0.17763.2183 custom x64-based Systems
CNA Microsoft Windows Server 2019 Server Core Installation affected 10.0.17763.0 10.0.17763.2183 custom x64-based Systems
CNA Microsoft Windows Server 2022 affected 10.0.20348.0 10.0.20348.230 custom x64-based Systems
CNA Microsoft Windows Server Version 2004 affected 10.0.0 10.0.19041.1237 custom x64-based Systems
CNA Microsoft Windows Server Version 20H2 affected 10.0.0 10.0.19042.1237 custom x64-based Systems

References

ReferenceSourceLinkTags
msrc.microsoft.com/update-guide/vulnerability/CVE-2021-40444 [email protected] msrc.microsoft.com Patch, Vendor Advisory
www.cisa.gov/known-exploited-vulnerabilities-catalog 134c704f-9b21-4f2e-91b3-4a467353bcc0 www.cisa.gov US Government Resource
Microsoft Windows MSHTML Overview ≈ Packet Storm af854a3a-2127-422b-91ae-364da2661108 packetstormsecurity.com Third Party Advisory, VDB Entry
Microsoft Office Word MSHTML Remote Code Execution ≈ Packet Storm af854a3a-2127-422b-91ae-364da2661108 packetstormsecurity.com Exploit, Third Party Advisory, VDB Entry
Security Update Guide - Microsoft Security Response Center af854a3a-2127-422b-91ae-364da2661108 portal.msrc.microsoft.com Mitigation, Patch, Vendor Advisory
Microsoft Office MSDT Follina Proof Of Concept ≈ Packet Storm af854a3a-2127-422b-91ae-364da2661108 packetstormsecurity.com Exploit, Third Party Advisory, VDB Entry
CVE Program record CVE.ORG www.cve.org canonical
NVD vulnerability detail NVD nvd.nist.gov canonical, analysis
CISA Known Exploited Vulnerabilities catalog CISA www.cisa.gov kev

Legacy QID Mappings

  • 91814 Microsoft MSHTML Remote Code Execution (RCE) Vulnerability

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