CVE-2021-40444 Microsoft MSHTML Remote Code Execution
Attackers can execute arbitrary code by tricking users into opening malicious Office documents that exploit a path traversal flaw in the MSHTML rendering engine.
- Exploited in the wild
- Since 3 Nov 2021
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- A user has to click or open something
- Fix
- Available
What is CVE-2021-40444?
CVE-2021-40444 is a high-severity path traversal vulnerability in Microsoft Windows 10 1507, published on 15 Sep 2021. An attacker can exploit it over the internet without logging in, and only if a user opens a file or follows a link.
Official 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.
Weakness: CWE-22
Which versions are affected by CVE-2021-40444?
It affects 17 products.
Products include Microsoft Windows 10 1507, Microsoft Windows 10 1607, Microsoft Windows 10 1809, Microsoft Windows 10 1909, Microsoft Windows 10 2004, Microsoft Windows 10 20h2 and 11 more.
How do I fix CVE-2021-40444?
Apply the vendor's patch. US federal agencies must fix it by 17 Nov 2021.
Upgrade, and resolve every user-supplied path against an allowed base folder before opening it. More about Path traversal.
Is CVE-2021-40444 being exploited?
Yes. Attackers have exploited CVE-2021-40444 in the wild since at least 3 Nov 2021, including in ransomware campaigns.
Public exploit code: 1 Metasploit module and 35 proofs of concept on GitHub.
Other vulnerabilities in Microsoft Windows 10 1507
- CVE-2017-8543 Microsoft Windows Search Remote Code Execution
- CVE-2025-33053 Microsoft Windows External Control of File Name or Path
- CVE-2025-33073 Microsoft Windows SMB Client Improper Access Control
- CVE-2024-49039 Microsoft Windows Task Scheduler Privilege Escalation
- CVE-2024-43461 Microsoft Windows MSHTML Platform Spoofing
Sources
Also known as GHSA-2h32-fhf6-xhh5, openSUSE-SU-2024:13674-1.