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AUSCERT Security Bulletin
ASB-2021.0177.2
Microsoft MSHTML Remote Code Execution Vulnerability
15 September 2021
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AusCERT Security Bulletin Summary
---------------------------------
Product: MSHTML
Operating System: Windows
Impact/Access: Execute Arbitrary Code/Commands -- Remote with User Interaction
Resolution: Patch/Upgrade
CVE Names: CVE-2021-40444
Revision History: September 15 2021: Microsoft has released security updates to address this vulnerability
September 8 2021: Initial Release
OVERVIEW
Microsoft has released an advisory detailing a remote code execution
vulnerability in Windows that is currently being exploited in the
wild. CVE CVE-2021-40444 has been assigned to this vulnerability.
[1]
IMPACT
Microsoft has stated the following:
"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."
--------------------UPDATE 14/09/2021--------------------
Microsoft has released security updates to address this vulnerability. [1]
MITIGATION
Microsoft advises that by default, Microsoft Office opens documents
from the internet in Protected View or Application Guard for Office
both of which prevent the current attack. [1]
Microsoft also advises that disabling the installation of all
ActiveX controls in Internet Explorer mitigates this attack. [1]
Microsoft Defender Antivirus and Microsoft Defender for Endpoint
both provide detection and protections for the known vulnerability.
[1]
--------------------UPDATE 14/09/2021--------------------
Microsoft has released security updates to address this vulnerability. [1]
REFERENCES
[1] Microsoft MSHTML Remote Code Execution Vulnerability
https://msrc.microsoft.com/update-guide/vulnerability/CVE-2021-40444
AusCERT has made every effort to ensure that the information contained
in this document is accurate. However, the decision to use the information
described is the responsibility of each user or organisation. The decision to
follow or act on information or advice contained in this security bulletin is
the responsibility of each user or organisation, and should be considered in
accordance with your organisation's site policies and procedures. AusCERT
takes no responsibility for consequences which may arise from following or
acting on information or advice contained in this security bulletin.
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Australian Computer Emergency Response Team
The University of Queensland
Brisbane
Qld 4072
Internet Email: auscert@auscert.org.au
Facsimile: (07) 3365 7031
Telephone: (07) 3365 4417 (International: +61 7 3365 4417)
AusCERT personnel answer during Queensland business hours
which are GMT+10:00 (AEST).
On call after hours for member emergencies only.
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