CVE-2021-40444
<p>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.</p> <p>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.</p> <p>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”.</p> <p>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.</p> <p>Please see the <strong>Mitigations</strong> and <strong>Workaround</strong> sections for important information about steps you can take to protect your system from this vulnerability.</p> <p><strong>UPDATE</strong> 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.</p>
| Software | From | Fixed in |
|---|---|---|
| microsoft / windows_server_2008 | r2-sp1 | r2-sp1.x |
| microsoft / windows_server_2008 | --sp2 | --sp2.x |
| microsoft / windows_server_2012 | --r2 | --r2.x |
| microsoft / windows_7 | --sp1 | --sp1.x |
| microsoft / windows_server_2022 | - | 10.0.20348.230 |
| microsoft / windows_10_1809 | - | 10.0.17763.2183 |
| microsoft / windows_10_1909 | - | 10.0.18363.1801 |
| microsoft / windows_10_21h1 | - | 10.0.19043.1237 |
| microsoft / windows_10_2004 | - | 10.0.19041.1237 |
| microsoft / windows_server_2004 | - | 10.0.19041.1237 |
| microsoft / windows_10_20h2 | - | 10.0.19042.1237 |
| microsoft / windows_server_20h2 | - | 10.0.19042.1237 |
| microsoft / windows_10_1507 | - | 10.0.10240.19060 |
| microsoft / windows_10_1607 | - | 10.0.14393.4651 |
| microsoft / windows_server_2016 | - | 10.0.14393.4651 |
| microsoft / windows_server_2019 | - | 10.0.17763.2183 |
- http://packetstormsecurity.com/files/164210/Microsoft-Windows-MSHTML-Overview.html
- http://packetstormsecurity.com/files/165214/Microsoft-Office-Word-MSHTML-Remote-Code-Execution.html
- http://packetstormsecurity.com/files/167317/Microsoft-Office-MSDT-Follina-Proof-Of-Concept.html
- https://portal.msrc.microsoft.com/en-US/security-guidance/advisory/CVE-2021-40444
- https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2021-40444
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Frequently Asked Questions
A security vulnerability is a weakness in software, hardware, or configuration that can be exploited to compromise confidentiality, integrity, or availability. Many vulnerabilities are tracked as CVEs (Common Vulnerabilities and Exposures), which provide a standardized identifier so teams can coordinate patching, mitigation, and risk assessment across tools and vendors.
CVSS (Common Vulnerability Scoring System) estimates technical severity, but it doesn't automatically equal business risk. Prioritize using context like internet exposure, affected asset criticality, known exploitation (proof-of-concept or in-the-wild), and whether compensating controls exist. A "Medium" CVSS on an exposed, production system can be more urgent than a "Critical" on an isolated, non-production host.
A vulnerability is the underlying weakness. An exploit is the method or code used to take advantage of it. A zero-day is a vulnerability that is unknown to the vendor or has no publicly available fix when attackers begin using it. In practice, risk increases sharply when exploitation becomes reliable or widespread.
Recurring findings usually come from incomplete Asset Discovery, inconsistent patch management, inherited images, and configuration drift. In modern environments, you also need to watch the software supply chain: dependencies, containers, build pipelines, and third-party services can reintroduce the same weakness even after you patch a single host. Unknown or unmanaged assets (often called Shadow IT) are a common reason the same issues resurface.
Use a simple, repeatable triage model: focus first on externally exposed assets, high-value systems (identity, VPN, email, production), vulnerabilities with known exploits, and issues that enable remote code execution or privilege escalation. Then enforce patch SLAs and track progress using consistent metrics so remediation is steady, not reactive.
SynScan combines attack surface monitoring and continuous security auditing to keep your inventory current, flag high-impact vulnerabilities early, and help you turn raw findings into a practical remediation plan.