Alert - Active Exploitation of Microsoft MSHTML Remote Code Execution Vulnerability - update 1

Number: AL21-018 UPDATE 1
Date: 8 September 2021
Updated: 14 September 2021

AUDIENCE

This Alert is intended for IT professionals and managers of notified organizations.

PURPOSE

An Alert is used to raise awareness of a recently identified cyber threat Cyber threatA threat actor, using the internet, who takes advantage of a known vulnerability in a product for the purposes of exploiting a network and the information the network carries. that may impact cyber information assets, and to provide additional detection DetectionThe monitoring and analyzing of system events in order to identify unauthorized attempts to access system resources. and mitigation advice to recipients. The Canadian Centre for Cyber Security Cyber securityThe protection of digital information, as well as the integrity of the infrastructure housing and transmitting digital information. More specifically, cyber security includes the body of technologies, processes, practices and response and mitigation measures designed to protect networks, computers, programs and data from attack, damage or unauthorized access so as to ensure confidentiality, integrity and availability. ("Cyber Centre") is also available to provide additional assistance regarding the content of this Alert to recipients as requested.

OVERVIEW

The Cyber Centre is aware of reported ongoing scanning and exploitation of an unpatched remote code execution vulnerability VulnerabilityA flaw or weakness in the design or implementation of an information system or its environment that could be exploited to adversely affect an organization's assets or operations. in MSHTML affecting Microsoft Windows [1]. Microsoft has released guidance to mitigate this vulnerability.

DETAILS

On 7 September 2021 Microsoft released a KB article [1] detailing an unpatched remote code execution vulnerability, tracked as CVE-2021-40444, in MSHTML affecting multiple versions of Microsoft Windows. Exploitation of this vulnerability could involve the creation of a malicious ActiveX control to be used by a Microsoft Office document that hosts the browser rendering engine.

Successful exploitation requires user interaction to open a malicious document and then enable editing. By default, Microsoft Office prevents exploitation of this vulnerability by opening documents from the Internet in Protected View or Application Guard GuardA gateway that is placed between two networks, computers, or other information systems that operate at different security levels. The guard mediates all information transfers between the two levels so that no sensitive information from the higher security level is disclosed to the lower level. It also protects the integrity of data on the higher level. for Office.

Microsoft reports that this vulnerability has been publicly disclosed and that it is aware of targeted attempts at exploitation using specially crafted Microsoft Office documents [1][2].

MITIGATION

UPDATE 1
On 14 September 2021, a patch for CVE-2021-40444 was released as part of the September 2021 Security Updates [1].

Microsoft outlines a workaround to mitigate this vulnerability as part of the KB article released on 7 September 2021.

The Cyber Centre encourages organizations to review the Microsoft KB article [1] for detailed information.

DETECTION

Microsoft indicates that both Microsoft Defender Antivirus and Microsoft Defender for Endpoint can detect and protect against CVE-2021-40444 [1].

The Cyber Centre encourages organizations to ensure their anti-virus software Anti-virus softwareSoftware that defends against viruses, Trojans, worms, and spyware. Anti-virus software uses a scanner to identify programs that may be malicious. Scanners can detect known viruses, previously unknown viruses, and suspicious files. is up to date [3].

REFERENCES

[1] Windows KB Article – CVE-2021-40444

[2] CISA - Microsoft Releases Mitigations and Workarounds for CVE-2021-40444

[3] Protect Your Organization From Malware (ITSAP.00.057)

NOTE TO READERS

The Canadian Centre for Cyber Security (Cyber Centre) operates as part of the Communications Security Establishment. We are Canada's national authority on cyber security and we lead the government's response to cyber security events. As Canada's national computer security incident response team, the Cyber Centre works in close collaboration with government departments, critical infrastructure Critical infrastructureProcesses, systems, facilities, technologies, networks, assets, and services essential to the health, safety, security, or economic well-being of Canadians and the effective functioning of government. Critical infrastructure can be stand-alone or interconnected and interdependent within and across provinces, territories, and national borders. Disruptions of critical infrastructure could result in catastrophic loss of life, adverse economic effects, and significant harm to public confidence. , Canadian businesses and international partners to prepare for, respond to, mitigate, and recover from cyber events. We do this by providing authoritative advice and support, and coordinating information sharing and incident response. The Cyber Centre is outward-facing, welcoming partnerships that help build a stronger, more resilient cyber space in Canada.