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.
Attack profile
How easy it is to exploit
- Attack vector
- Network
- Complexity
- Low
- Privileges needed
- None
- User interaction
- Required
What an attacker can affect
- Confidentiality
- Low
- Integrity
- High
- Availability
- Low
Exploit likelihood
What each source reports
CVE List Score used
8.8
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.
- Record
CVE-2021-40444- CVSS 3.1
- 8.8 High
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 - Weakness
- CWE-22
- Updated
- 2026-11-02
EUVDEUVD-2021-27621
8.8
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.
- Record
EUVD-2021-27621- CVSS 3.1
- 8.8 High
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 - Updated
- 2026-11-02
GitHub AdvisoriesGHSA-2h32-fhf6-xhh5
7.8
Microsoft MSHTML Remote Code Execution Vulnerability
Microsoft MSHTML Remote Code Execution Vulnerability
- Record
GHSA-2h32-fhf6-xhh5- CVSS 3.1
- 7.8 High
CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H - Weakness
- CWE-22
- Updated
- 2026-11-02
CISA KEV No score
Microsoft MSHTML Remote Code Execution Vulnerability
Microsoft MSHTML contains a unspecified vulnerability that allows for remote code execution.
- Record
CVE-2021-40444- Weakness
- CWE-22
- Updated
- 2026-11-02
NVD
8.8
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.
- Record
CVE-2021-40444- CVSS 3.1
- 8.8 High
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:H/A:L - CVSS 3.1
- 7.8 High
CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H - CVSS 2.0
- 6.8 Medium
AV:N/AC:M/Au:N/C:P/I:P/A:P - Weakness
- CWE-22
- Updated
- 2026-11-02
OSVopenSUSE-SU-2024:13674-1 No score
python310-oletools-0.60.1-1.1 on GA media
These are all security issues fixed in the python310-oletools-0.60.1-1.1 package on the GA media of openSUSE Tumbleweed.
- Record
openSUSE-SU-2024:13674-1- Updated
- 2026-11-02
OSVopenSUSE-SU-2026:12022-1 No score
python313-oletools-0.60.2-2.4 on GA media
These are all security issues fixed in the python313-oletools-0.60.2-2.4 package on the GA media of openSUSE Tumbleweed.
- Record
openSUSE-SU-2026:12022-1- Updated
- 2026-11-02
Affected products
- microsoft mshtml
- microsoft windows 10 version 1507
- microsoft windows 10 version 1607
- microsoft windows 10 version 1809
- microsoft windows 10 version 1909
- microsoft windows 10 version 2004
- microsoft windows 10 version 20h2
- microsoft windows 10 version 21h1
- microsoft windows 7
- microsoft windows 7 service pack 1
- microsoft windows 8.1
- microsoft windows server 2008 r2 service pack 1
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- microsoft windows server 2008 r2 service pack 1 (server core installation)
- microsoft windows server 2008 service pack 2
- microsoft windows server 2008 service pack 2 (server core installation)
- microsoft windows server 2012
- microsoft windows server 2012 (server core installation)
- microsoft windows server 2012 r2
- microsoft windows server 2012 r2 (server core installation)
- microsoft windows server 2016
- microsoft windows server 2016 (server core installation)
- microsoft windows server 2019
- microsoft windows server 2019 (server core installation)
- microsoft windows server 2022
- microsoft windows server version 2004
- microsoft windows server version 20h2
- microsoft windows 10 1507
- microsoft windows 10 1607
- microsoft windows 10 1809
- microsoft windows 10 1909
- microsoft windows 10 2004
- microsoft windows 10 20h2
- microsoft windows 10 21h1
- microsoft windows rt 8.1
- microsoft windows server 2004
- microsoft windows server 2008
- microsoft windows server 20h2
Affected packages
| Package | Affected | Fixed |
|---|---|---|
python-oletoolsopenSUSE:Tumbleweed From an advisory covering 2 CVEs |
before 0.60.2-2.4 | 0.60.2-2.4 |
Public exploits
Links only. Every CVE stores no exploit code.
| Source | Link | Date |
|---|---|---|
| PoC in GitHub | ozergoker/CVE-2021-40444 | 2021-09-08 |
| PoC in GitHub | DarkSprings/CVE-2021-40444 | 2021-09-09 |
| PoC in GitHub | Immersive-Labs-Sec/cve-2021-40444-analysis | 2021-09-09 |
| PoC in GitHub | bambooqj/CVE-2021-40444_EXP_JS | 2021-09-09 |
| PoC in GitHub | rfcxv/CVE-2021-40444-POC | 2021-09-09 |
| PoC in GitHub | vysecurity/CVE-2021-40444 | 2021-09-09 |
| PoC in GitHub | k4k4/CVE-2021-40444-Sample | 2021-09-10 |
| PoC in GitHub | lockedbyte/CVE-2021-40444 | 2021-09-10 |
| PoC in GitHub | KnoooW/CVE-2021-40444-docx-Generate | 2021-09-11 |
| PoC in GitHub | fengjixuchui/CVE-2021-40444-docx-Generate | 2021-09-11 |
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| Source | Link | Date |
|---|---|---|
| PoC in GitHub | mansk1es/Caboom | 2021-09-11 |
| PoC in GitHub | W1kyri3/Exploit-PoC-CVE-2021-40444-inject-ma-doc-vao-docx | 2021-09-12 |
| PoC in GitHub | aslitsecurity/CVE-2021-40444_builders | 2021-09-12 |
| PoC in GitHub | jamesrep/cve-2021-40444 | 2021-09-12 |
| PoC in GitHub | Jeromeyoung/MSHTMHell | 2021-09-14 |
| PoC in GitHub | k8gege/CVE-2021-40444 | 2021-09-14 |
| PoC in GitHub | m4madturk/CVE-2021-40444 | 2021-09-14 |
| PoC in GitHub | klezVirus/CVE-2021-40444 | 2021-09-15 |
| PoC in GitHub | Edubr2020/CVE-2021-40444--CABless | 2021-09-19 |
| Metasploit | Microsoft Office Word Malicious MSHTML RCE | 2021-09-23 |
| PoC in GitHub | kal1gh0st/CVE-2021-40444_CAB_archives | 2021-09-24 |
| PoC in GitHub | LazarusReborn/Docx-Exploit-2021 | 2021-09-29 |
| PoC in GitHub | H0j3n/CVE-2021-40444 | 2021-10-03 |
| PoC in GitHub | metehangenel/MSHTML-CVE-2021-40444 | 2021-10-15 |
| PoC in GitHub | Jeromeyoung/TIC4301_Project | 2021-10-16 |
| PoC in GitHub | tiagob0b/CVE-2021-40444 | 2021-10-24 |
Plus 10 more. The full list has every link.
History
| Recorded | Changed | Sources |
|---|---|---|
| affected, facts | ||
| exploitation | ||
| exploits, exploits_more | ||
| first indexed | CVE List, EUVD, GitHub Advisories, CISA KEV, Metasploit, NVD, OSV, PoC in GitHub |
Dates are when Every CVE recorded each change. Upstream dates may differ.
In short
CVE-2021-40444 is a high vulnerability (CVSS 8.8) in Microsoft Mshtml, published September 15, 2021. CISA lists it as known to be exploited, since November 3, 2021. EUVD reports exploitation since November 3, 2021. Public exploit code exists. EPSS puts the chance of exploitation in the next 30 days at 97.8%, the 99th percentile. No source names a fixed version.
References
msrc.microsoft.com/update-guide/vulnerability/CVE-2021-40444
portal.msrc.microsoft.com/en-US/security-guidance/advisory/CVE-2021-40444
packetstormsecurity.com/files/164210/Microsoft-Windows-MSHTML-Overview.html
packetstormsecurity.com/files/165214/Microsoft-Office-Word-MSHTML-Remote-Code-Execution.html
packetstormsecurity.com/files/167317/Microsoft-Office-MSDT-Follina-Proof-Of-Concept.html
cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2021-40444