OnlyFm252
Windows MSHTML Platform

CVE-2021-40444 — Microsoft MSHTML Remote Code Execution Vulnerability

Important CVSS 8.8 EPSS 0.97242 ⚠️ Exploited in the wild 📢 Publicly disclosed 2021-09 archive

Executive Summary

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.

Overview

8.8
CVSS HIGH
Important
MS Severity
Exploited
MS Exploit Status
Exploitation Detected
MS Exploit Likelihood
Category Remote Code Execution
Released Sep 14 2021
Last Updated Sep 14 2021
Publicly Disclosed Yes
CISA KEV Not Listed
Known Exploits None Known
EPSS Score 0.97242 — 0.99887 percentile
NVD CVSS 8.8 HIGH — matches MSRC

CVSS Vector

CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:H/A:L/E:P/RL:O/RC:C
ATTACK VECTOR
Network
ATTACK COMPLEXITY
Low
PRIVILEGES REQUIRED
None
USER INTERACTION
Required
SCOPE
Changed
CONFIDENTIALITY
Low
INTEGRITY
High
AVAILABILITY
Low
EXPLOIT CODE MATURITY
Proof-of-Concept
REMEDIATION LEVEL
Official Fix
REPORT CONFIDENCE
Confirmed
Temporal Score: 7.9

EPSS Score

0.97242
probability of exploitation in the next 30 days
0.99887 percentile - updated 2026-06-21
View on FIRST.org

Affected Products

28 affected products
Product KB Article Severity Impact Restart Required
Windows 10 for 32-bit Systems 5005569 (Security Update) Important Remote Code Execution Yes
Windows 10 for x64-based Systems 5005569 (Security Update) Important Remote Code Execution Yes
Windows 10 Version 1607 for 32-bit Systems 5005573 (Security Update) Important Remote Code Execution Yes
Windows 10 Version 1607 for x64-based Systems 5005573 (Security Update) Important Remote Code Execution Yes
Windows 10 Version 1809 for 32-bit Systems 5005568 (Security Update) Important Remote Code Execution Yes
Windows 10 Version 1809 for ARM64-based Systems 5005568 (Security Update) Important Remote Code Execution Yes
Windows 10 Version 1809 for x64-based Systems 5005568 (Security Update) Important Remote Code Execution Yes
Windows 10 Version 1909 for 32-bit Systems 5005566 (Security Update) Important Remote Code Execution Yes
Windows 10 Version 1909 for ARM64-based Systems 5005566 (Security Update) Important Remote Code Execution Yes
Windows 10 Version 1909 for x64-based Systems 5005566 (Security Update) Important Remote Code Execution Yes
Windows 10 Version 2004 for 32-bit Systems 5005565 (Security Update) Important Remote Code Execution Yes
Windows 10 Version 2004 for ARM64-based Systems 5005565 (Security Update) Important Remote Code Execution Yes
Windows 10 Version 2004 for x64-based Systems 5005565 (Security Update) Important Remote Code Execution Yes
Windows 10 Version 20H2 for 32-bit Systems 5005565 (Security Update) Important Remote Code Execution Yes
Windows 10 Version 20H2 for ARM64-based Systems 5005565 (Security Update) Important Remote Code Execution Yes
Windows 10 Version 20H2 for x64-based Systems 5005565 (Security Update) Important Remote Code Execution Yes
Windows 10 Version 21H1 for 32-bit Systems 5005565 (Security Update) Important Remote Code Execution Yes
Windows 10 Version 21H1 for ARM64-based Systems 5005565 (Security Update) Important Remote Code Execution Yes
Windows 10 Version 21H1 for x64-based Systems 5005565 (Security Update) Important Remote Code Execution Yes
Windows 7 for 32-bit Systems Service Pack 1 5005633 (Monthly Rollup) 5005563 (IE Cumulative) 5019958 (IE Cumulative) Important Remote Code Execution 5005088 5005036 Base: 8.8 Temporal: 7.9 Vector: CVSS:3.0/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:H/A:L/E:P/RL:O/RC:C 6.1.7601.25712 6.1.7601.26221 Yes 5005633 Windows 7 for x64-based Systems Service Pack 1 5005633 (Monthly Rollup) 5005563 (IE Cumulative) 5019958 (IE Cumulative) Important Remote Code Execution 5005088 5005036 Base: 8.8 Temporal: 7.9 Vector: CVSS:3.0/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:H/A:L/E:P/RL:O/RC:C 6.1.7601.25712 6.1.7601.26221 Yes 5005633 Windows 8.1 for 32-bit systems 5005613 (Monthly Rollup) 5005627 (Security Only) 5005563 (IE Cumulative) Important Remote Code Execution 5005076 5005036 Base: 8.8 Temporal: 7.9 Vector: CVSS:3.0/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:H/A:L/E:P/RL:O/RC:C 6.3.9600.20120 Yes 5005613 5005627 Windows 8.1 for x64-based systems 5005613 (Monthly Rollup) 5005627 (Security Only) 5005563 (IE Cumulative) Important Remote Code Execution 5005076 5005036 Base: 8.8 Temporal: 7.9 Vector: CVSS:3.0/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:H/A:L/E:P/RL:O/RC:C 6.3.9600.20120 Yes 5005613 5005627 Windows RT 8.1 5005613 (Monthly Rollup) Important Remote Code Execution Yes
Windows Server 2008 for 32-bit Systems Service Pack 2 5005563 (IE Cumulative) 5005606 (Monthly Rollup) Important Remote Code Execution 5005036 5005090 Base: 8.8 Temporal: 7.9 Vector: CVSS:3.0/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:H/A:L/E:P/RL:O/RC:C 6.0.6003.21218 Yes 5005606 Windows Server 2008 for 32-bit Systems Service Pack 2 (Server Core installation) 5005563 (IE Cumulative) 5005606 (Monthly Rollup) Important Remote Code Execution 5005036 5005090 Base: 8.8 Temporal: 7.9 Vector: CVSS:3.0/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:H/A:L/E:P/RL:O/RC:C 6.0.6003.21218 Yes 5005606 Windows Server 2008 for x64-based Systems Service Pack 2 5005563 (IE Cumulative) 5005606 (Monthly Rollup) Important Remote Code Execution 5005036 5005090 Base: 8.8 Temporal: 7.9 Vector: CVSS:3.0/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:H/A:L/E:P/RL:O/RC:C 6.0.6003.21218 Yes 5005606 Windows Server 2008 for x64-based Systems Service Pack 2 (Server Core installation) 5005563 (IE Cumulative) 5005606 (Monthly Rollup) Important Remote Code Execution 5005036 5005090 Base: 8.8 Temporal: 7.9 Vector: CVSS:3.0/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:H/A:L/E:P/RL:O/RC:C 6.0.6003.21218 Yes 5005606 Windows Server 2008 R2 for x64-based Systems Service Pack 1 5005633 (Monthly Rollup) 5005563 (IE Cumulative) Important Remote Code Execution 5005088 5005036 Base: 8.8 Temporal: 7.9 Vector: CVSS:3.0/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:H/A:L/E:P/RL:O/RC:C 6.1.7601.25712 Yes 5005633 Windows Server 2008 R2 for x64-based Systems Service Pack 1 (Server Core installation) 5005633 (Monthly Rollup) 5005563 (IE Cumulative) Important Remote Code Execution 5005088 5005036 Base: 8.8 Temporal: 7.9 Vector: CVSS:3.0/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:H/A:L/E:P/RL:O/RC:C 6.1.7601.25712 Yes 5005633 Windows Server 2012 5005623 (Monthly Rollup) 5005563 (IE Cumulative) Important Remote Code Execution 5005094 5005036 Base: 8.8 Temporal: 7.9 Vector: CVSS:3.0/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:H/A:L/E:P/RL:O/RC:C 6.2.9200.23462 v1.001 Yes 5005623 Windows Server 2012 (Server Core installation) 5005623 (Monthly Rollup) 5005563 (IE Cumulative) Important Remote Code Execution 5005094 5005036 Base: 8.8 Temporal: 7.9 Vector: CVSS:3.0/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:H/A:L/E:P/RL:O/RC:C 6.2.9200.23462 v1.001 Yes 5005623 Windows Server 2012 R2 5005613 (Monthly Rollup) 5005563 (IE Cumulative) Important Remote Code Execution 5005076 5005036 Base: 8.8 Temporal: 7.9 Vector: CVSS:3.0/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:H/A:L/E:P/RL:O/RC:C 6.3.9600.20120 Yes 5005613 Windows Server 2012 R2 (Server Core installation) 5005613 (Monthly Rollup) 5005563 (IE Cumulative) Important Remote Code Execution 5005076 5005036 Base: 8.8 Temporal: 7.9 Vector: CVSS:3.0/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:H/A:L/E:P/RL:O/RC:C 6.3.9600.20120 Yes 5005613 Windows Server 2016 5005573 (Security Update) Important Remote Code Execution Yes
Windows Server 2016 (Server Core installation) 5005573 (Security Update) Important Remote Code Execution Yes
Windows Server 2019 5005568 (Security Update) Important Remote Code Execution Yes
Windows Server 2019 (Server Core installation) 5005568 (Security Update) Important Remote Code Execution Yes
Windows Server 2022 5005575 (Security Update) Important Remote Code Execution Yes
Windows Server 2022 (Server Core installation) 5005575 (Security Update) Important Remote Code Execution Yes
Windows Server, version 2004 (Server Core installation) 5005565 (Security Update) Important Remote Code Execution Yes
Windows Server, version 20H2 (Server Core Installation) 5005565 (Security Update) Important Remote Code Execution Yes

Patches

7 patches
Article Type Restart
5005569 Security Update Yes
5005573 Security Update Yes
5005568 Security Update Yes
5005566 Security Update Yes
5005565 Security Update Yes
5005613 Monthly Rollup Yes
5005575 Security Update Yes

Known Exploits

Acknowledgments

Bryce Abdo of Mandiant, Haifei Li of EXPMON, Genwei Jiang of Mandiant, Rick Cole (MSTIC), Dhanesh Kizhakkinan of Mandiant

On This Page