CVE-2021-40444

What it is

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.

At a glance

Exploitability

Can be exploited over the network without logging in, but needs a user to act. High risk of data tampering.

In the wild

CISA lists this as exploited in real attacks. Treat as urgent.

Fix

A patch, advisory or fixed version is referenced. Upgrade or apply it.

Timeline

1. 2021-09-02 00:00 UTC ReservedThe CVE id was reserved by its CNA
2. 2021-09-15 12:15 UTC PublishedDisclosed publicly on CVE.org and NVD
3. 2021-11-03 Exploited in the wildAdded to CISA's Known Exploited Vulnerabilities list
4. 2021-11-17 Remediation deadlineCISA's due date for federal agencies to fix it
5. 2026-08-10 20:19 UTC Last updatedMost recent change to the record

Why it ranks here

• Exploited in the wild: yes, CISA lists it. This puts it above everything that is not.
• Exploit odds: 97.8% in the next 30 days (EPSS).
• Severity: 8.8 HIGH (CVSS).
• Fix: a patch or advisory is linked.

Details

Published

2021-09-15 12:15 UTC

Last modified

2026-08-10 20:19 UTC

Added to CISA KEV

2021-11-03

Exploit probability

97.8% · EPSS, next 30 days

Weakness

CWE-22 · Path traversal

Record status

Analyzed

Affected

• Microsoft Windows 10 1507 < 10.0.10240.19060
• Microsoft Windows 10 1607 < 10.0.14393.4651
• Microsoft Windows 10 1809 < 10.0.17763.2183
• Microsoft Windows 10 1909 < 10.0.18363.1801
• Microsoft Windows 10 2004 < 10.0.19041.1237
• Microsoft Windows 10 20h2 < 10.0.19042.1237
• Microsoft Windows 10 21h1 < 10.0.19043.1237
• Microsoft Windows 7

Attack profile CVSS 3.1 · 8.8

Attack vector

Network

Complexity

Low

Privileges needed

None

User interaction

Required

Scope

Changed

Confidentiality

Low

Integrity

High

Availability

Low

Is it in your code?

Hand this to your coding agent. It searches your project for the affected products and checks versions. Nothing leaves your machine.

Read https://cve-list.com/agent/cve/CVE-2021-40444.md and follow it. Check whether this project is affected by CVE-2021-40444. Read only. Don't change anything and don't upload my code. Tell me yes, no or not sure, with the file as proof.

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