<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>
Published 2021-09-15 12:15:16
Updated 2023-12-28 20:16:07
View at NVD,   CVE.org
Vulnerability category: Directory traversalExecute code

CVE-2021-40444 is in the CISA Known Exploited Vulnerabilities Catalog

This issue is known to have been leveraged as part of a ransomware campaign.
CISA vulnerability name:
Microsoft MSHTML Remote Code Execution Vulnerability
CISA required action:
Apply updates per vendor instructions.
CISA description:
Microsoft MSHTML contains a unspecified vulnerability that allows for remote code execution.
Added on 2021-11-03 Action due date 2021-11-17

Exploit prediction scoring system (EPSS) score for CVE-2021-40444

Probability of exploitation activity in the next 30 days: 96.87%

Percentile, the proportion of vulnerabilities that are scored at or less: ~ 100 % EPSS Score History EPSS FAQ

Metasploit modules for CVE-2021-40444

  • Microsoft Office Word Malicious MSHTML RCE
    Disclosure Date: 2021-09-23
    First seen: 2022-12-23
    exploit/windows/fileformat/word_mshtml_rce
    This module creates a malicious docx file that when opened in Word on a vulnerable Windows system will lead to code execution. This vulnerability exists because an attacker can craft a malicious ActiveX control to be used by a Microsoft Office document that hosts

CVSS scores for CVE-2021-40444

Base Score Base Severity CVSS Vector Exploitability Score Impact Score Score Source
6.8
MEDIUM AV:N/AC:M/Au:N/C:P/I:P/A:P
8.6
6.4
NIST
7.8
HIGH CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H
1.8
5.9
NIST
8.8
HIGH CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:H/A:L
2.8
5.3
Microsoft Corporation

CWE ids for CVE-2021-40444

  • The product uses external input to construct a pathname that is intended to identify a file or directory that is located underneath a restricted parent directory, but the product does not properly neutralize special elements within the pathname that can cause the pathname to resolve to a location that is outside of the restricted directory.
    Assigned by: nvd@nist.gov (Primary)

References for CVE-2021-40444

Products affected by CVE-2021-40444

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