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>
ACTIVELY EXPLOITED IN THE WILD
This vulnerability is listed in the CISA Known Exploited Vulnerabilities (KEV) catalog.
Microsoft MSHTML Remote Code Execution Vulnerability
Microsoft MSHTML
Apply updates per vendor instructions.
11/3/2021
https://nvd.nist.gov/vuln/detail/CVE-2021-40444
Vulnerability Summary
CVSS v3 Score
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:H/A:L
CVSS v2 Score
AV:N/AC:M/Au:N/C:P/I:P/A:P
EPSS Score (Exploitation Probability)
This vulnerability has a 94.33% probability of being exploited in the next 30 days, ranking higher than 100% of all scored CVEs.
CWE Classification
Related Vulnerabilities
Same Weakness Type(CWE-22)
A vulnerability was detected in Flux159 mcp-game-asset-gen 0.1.0. Affected is the function image_to_3d_async of the file src/index.ts of the component MCP Interface. The manipulation of the argument statusFile results in path traversal. The attack can be executed remotely. The exploit is now public and may be used. The project was informed of the problem early through an issue report but has not responded yet.
The Snow Monkey Forms plugin for WordPress is vulnerable to arbitrary file deletion due to insufficient file path validation in the 'generate_user_dirpath' function in all versions up to, and including, 12.0.3. This makes it possible for unauthenticated attackers to delete arbitrary files on the server, which can easily lead to remote code execution when the right file is deleted (such as wp-config.php).
Docmost is an open-source collaborative wiki and documentation software. From 0.21.0 to before 0.24.0, Docmost is vulnerable to Arbitrary File Write via Zip Import Feature (ZipSlip). In apps/server/src/integrations/import/utils/file.utils.ts, there are no validation on filename. This vulnerability is fixed in 0.24.0.
The Integration Opvius AI for WooCommerce plugin for WordPress is vulnerable to Path Traversal in all versions up to, and including, 1.3.0. This is due to the `process_table_bulk_actions()` function processing user-supplied file paths without authentication checks, nonce verification, or path validation. This makes it possible for unauthenticated attackers to delete or download arbitrary files on the server via the `wsaw-log[]` POST parameter, which can be leveraged to delete critical files like `wp-config.php` or read sensitive configuration files.
** Disputed ** An Information Disclosure vulnerability in CouchCMS 2.4 allow an Admin user to read arbitrary files via traversing directories back after back. It can Disclosure the source code or any other confidential information if weaponize accordingly. NOTE: A community member states that this is not a CouchCMS vulnerability and that if /\<file> is accessible it is a web-server configuration issue.
Similar SeverityHIGH
Improper link resolution before file access ('link following') in Microsoft Defender allows an authorized attacker to elevate privileges locally.
Improper neutralization of input during web page generation ('cross-site scripting') in Microsoft Exchange Server allows an unauthorized attacker to perform spoofing over a network.
An Improper Input Validation in Ivanti EPMM before versions 12.6.1.1, 12.7.0.1, and 12.8.0.1 allows a remotely authenticated user with administrative access to achieve remote code execution.
OpenClaw before 2026.4.22 contains a server-side request forgery vulnerability in the Zalo plugin's sendPhoto function that fails to validate outbound photo URLs through the SSRF guard. Attackers can bypass SSRF protection by providing malicious photo URLs to the Zalo Bot API, enabling unauthorized access to internal resources.
OpenClaw before 2026.4.22 contains an exec allowlist analysis vulnerability allowing shell expansion hiding in unquoted heredoc bodies. Attackers can bypass allowlist validation by embedding shell expansion tokens in heredoc bodies to execute unapproved commands at runtime.
Learn More
View this score breakdown or calculate a custom score
Learn how severity scores are calculated and what they mean
Best practices for deciding which vulnerabilities to address first
Essential guide to Common Vulnerabilities and Exposures
Understand how CVEs relate to underlying weakness types