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CVE-2021-40444

Microsoft MSHTML Remote Code Execution Vulnerability

8.8 HighIn KEVPublic exploit

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

97.8%Up 93.8 points since Sep 16, 2021
90%50%10%1%

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 HighCVSS: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 HighCVSS: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 HighCVSS: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 HighCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:H/A:L
CVSS 3.1
7.8 HighCVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H
CVSS 2.0
6.8 MediumAV: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

Show 25 moreShow less

Affected packages

Affected packages
PackageAffectedFixed
python-oletools
openSUSE: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.

Public exploits
SourceLinkDate
PoC in GitHubozergoker/CVE-2021-404442021-09-08
PoC in GitHubDarkSprings/CVE-2021-404442021-09-09
PoC in GitHubImmersive-Labs-Sec/cve-2021-40444-analysis2021-09-09
PoC in GitHubbambooqj/CVE-2021-40444_EXP_JS2021-09-09
PoC in GitHubrfcxv/CVE-2021-40444-POC2021-09-09
PoC in GitHubvysecurity/CVE-2021-404442021-09-09
PoC in GitHubk4k4/CVE-2021-40444-Sample2021-09-10
PoC in GitHublockedbyte/CVE-2021-404442021-09-10
PoC in GitHubKnoooW/CVE-2021-40444-docx-Generate2021-09-11
PoC in GitHubfengjixuchui/CVE-2021-40444-docx-Generate2021-09-11
Show 16 moreShow less
Public exploits
SourceLinkDate
PoC in GitHubmansk1es/Caboom2021-09-11
PoC in GitHubW1kyri3/Exploit-PoC-CVE-2021-40444-inject-ma-doc-vao-docx2021-09-12
PoC in GitHubaslitsecurity/CVE-2021-40444_builders2021-09-12
PoC in GitHubjamesrep/cve-2021-404442021-09-12
PoC in GitHubJeromeyoung/MSHTMHell2021-09-14
PoC in GitHubk8gege/CVE-2021-404442021-09-14
PoC in GitHubm4madturk/CVE-2021-404442021-09-14
PoC in GitHubklezVirus/CVE-2021-404442021-09-15
PoC in GitHubEdubr2020/CVE-2021-40444--CABless2021-09-19
MetasploitMicrosoft Office Word Malicious MSHTML RCE2021-09-23
PoC in GitHubkal1gh0st/CVE-2021-40444_CAB_archives2021-09-24
PoC in GitHubLazarusReborn/Docx-Exploit-20212021-09-29
PoC in GitHubH0j3n/CVE-2021-404442021-10-03
PoC in GitHubmetehangenel/MSHTML-CVE-2021-404442021-10-15
PoC in GitHubJeromeyoung/TIC4301_Project2021-10-16
PoC in GitHubtiagob0b/CVE-2021-404442021-10-24

Plus 10 more. The full list has every link.

History

History
RecordedChangedSources
affected, facts
exploitation
exploits, exploits_more
first indexedCVE 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

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