Moderate
CVE-2021-40444
CVE-2021-40444
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.
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Technical Analysis
- Vulnerable if default behaviour has been changed ( By default, Microsoft Office opens documents from the internet in Protected View or Application Guard for Office both of which prevent the current attack )
- Requires social engineering to be exploited
- Workaround easy to deploy
Technical Analysis
Sounds from Microsoft’s out-of-band advisory like this is seeing limited, targeted attacks and folks are only vulnerable in non-default configurations (i.e., “by default, Microsoft Office opens documents from the internet in Protected View or Application Guard for Office both of which prevent the current attack”). All this plus user interaction required = another social engineering opportunity for attackers with specific targets, but probably not a big concern as far as widespread, automated exploitation goes. No patch yet, but sounds like the most out-of-the-box mitigation is just to use the default option of opening docs in a protected manner.
Those are great, @NinjaOperator, thanks for sharing!
Technical Analysis
CVE-2021-40444
Vulnerability:
Microsoft MSHTML Remote Code Execution Vulnerability
- Tested with malicious
.exefile
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.
Conclusion:
- Security is not checked
- Just OPEN :D
Risk Assessment:
- This may well be a meterpreter malicious backdoor shell file
- This may well be a malicious MSI package or hidden bat file
Status:
- Low(Medium)
Fixed
- Windows 11
Source:
Reproduce:
Demo docx:
Demo VLC:
Technical Analysis
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.
A threat actor 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.
https://msrc.microsoft.com/update-guide/vulnerability/CVE-2021-40444
Update: Unnamed threat actors are exploiting this vulnerability to drop Cobalt Strike
https://twitter.com/h2jazi/status/1458794565968748545
CVSS V3 Severity and Metrics
General Information
Vendors
- microsoft
Products
- windows 10 1507,
- windows 10 1607,
- windows 10 1809,
- windows 10 1909,
- windows 10 2004,
- windows 10 20h2,
- windows 10 21h1,
- windows 7 -,
- windows 8.1 -,
- windows rt 8.1 -,
- windows server 2004,
- windows server 2008 -,
- windows server 2008 r2,
- windows server 2012 -,
- windows server 2016,
- windows server 2019,
- windows server 2022,
- windows server 20h2
Metasploit Modules
Exploited in the Wild
References
Miscellaneous
