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Microsoft zeroday MSHTML vulnerability

By 9 September 2021 CERT, SOC, Vulnerability
Microsoft zeroday MSHTML-beveiligingslek

This blog contains information about the Microsoft zeroday MSHTML (CVE-2021-40444) vulnerability. As soon as we have an update, we’ll add it to this post. More information about possible risks and details can be found at the bottom of this blog.

Update September 9, 2021

17:00 | On September 7, a vulnerability was revealed in MSHTML that could allow the attacker to execute code remotely. This concerns the ActiveX control.

An attacker could create a malicious ActiveX control that could be used by a Microsoft Office application 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 may be less affected than users in Administrator/Administrator status.

Microsoft Defender Antivirus and Microsoft Defender for Endpoint both provide detection and protection for this vulnerability. Customers using automatic updates do not need to take any additional action.

Disabling the installation of all ActiveX controls in Internet Explorer mitigates this attack.

Reason and background of this blog

This blog contains information about vulnerabilities, the possible risk and advice on how to prevent or limit damage. Below are the possible risks, details and background information.

Potential risk

According to Microsoft, this vulnerability has the following impact:
An attacker could create a malicious ActiveX control that could be used by a Microsoft Office application that hosts the browser rendering engine. The attacker would then have to convince the user to open the malicious document.

Detail info

The following CVE reference belongs to this vulnerability.

Background

More information about this vulnerability:

MSHTML is the Internet Explorer engine. Internet Explorer is an old browser that is part of modern operating systems and some other programs use it to process web content. Especially Microsoft Office applications such as Word and PowerPoint make use of this.

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