CVE-2021-40444: Microsoft MSHTML Remote Code Execution Vulnerability Alert

Microsoft writes:

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”.

Microsoft issues temporary repair suggestions to disable ActiveX controls on an individual system

1. Create a .reg file with the following content

   Windows Registry Editor Version 5.00
   
   [HKEY_LOCAL_MACHINE\SOFTWARE\Policies\Microsoft\Windows\CurrentVersion\Internet Settings\Zones\0]
   "1001"=dword:00000003
   "1004"=dword:00000003
   
   [HKEY_LOCAL_MACHINE\SOFTWARE\Policies\Microsoft\Windows\CurrentVersion\Internet Settings\Zones\1]
   "1001"=dword:00000003
   "1004"=dword:00000003
   
   [HKEY_LOCAL_MACHINE\SOFTWARE\Policies\Microsoft\Windows\CurrentVersion\Internet Settings\Zones\2]
   "1001"=dword:00000003
   "1004"=dword:00000003
   
   [HKEY_LOCAL_MACHINE\SOFTWARE\Policies\Microsoft\Windows\CurrentVersion\Internet Settings\Zones\3]
   "1001"=dword:00000003
   "1004"=dword:00000003

2. Double-click the .reg file
3. Restart the operating system

Suggest Reading: detecting the exploitation of the zero-day CVE-2021-40444 in Microsoft MSHTML