CVE-2021-40444
Confirmed PUBLISHEDMicrosoft MSHTML Remote Code Execution Vulnerability
Recommended Action
Prioritize remediation. Validate affected assets and apply vendor fixes on an accelerated timeline.
At a Glance
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.
- CVE Published
- Sep 15, 2021
- Exploitation Reported
- Nov 03, 2021
- CVSS
- 8.8 High
- EPSS
- —
Affected Versions
40 version rows · page 1 of 2
| Vendor | Product | Version | Status |
|---|---|---|---|
| Microsoft |
Windows 10 Version 1809
|
10.0.0 to < 10.0.17763.2183 |
Affected |
| Microsoft |
Windows Server 2019
|
10.0.0 to < 10.0.17763.2183 |
Affected |
| Microsoft |
Windows Server 2019 (Server Core installation)
|
10.0.0 to < 10.0.17763.2183 |
Affected |
| Microsoft |
Windows 10 Version 1909
|
10.0.0 to < 10.0.18363.1801 |
Affected |
| Microsoft |
Windows 10 Version 21H1
|
10.0.0 to < 10.0.19043.1237 |
Affected |
| Microsoft |
Windows Server 2022
|
10.0.0 to < 10.0.20348.230 |
Affected |
| Microsoft |
Windows 10 Version 2004
|
10.0.0 to < 10.0.19041.1237 |
Affected |
| Microsoft |
Windows Server version 2004
|
10.0.0 to < 10.0.19041.1237 |
Affected |
| Microsoft |
Windows 10 Version 20H2
|
10.0.0 to < 10.0.19042.1237 |
Affected |
| Microsoft |
Windows Server version 20H2
|
10.0.0 to < 10.0.19042.1237 |
Affected |
| Microsoft |
Windows 10 Version 1507
|
10.0.0 to < 10.0.10240.19060 |
Affected |
| Microsoft |
Windows 10 Version 1607
|
10.0.0 to < 10.0.14393.4651 |
Affected |
| Microsoft |
Windows Server 2016
|
10.0.0 to < 10.0.14393.4651 |
Affected |
| Microsoft |
Windows Server 2016 (Server Core installation)
|
10.0.0 to < 10.0.14393.4651 |
Affected |
| Microsoft |
Windows 7
|
6.1.0 to < 6.1.7601.25712 |
Affected |
| Microsoft |
Windows 7
|
6.1.0 to < 1.001 |
Affected |
| Microsoft |
Windows 7
|
6.1.0 to < 6.1.7601.26221 |
Affected |
| Microsoft |
Windows 7 Service Pack 1
|
6.1.0 to < 6.1.7601.25712 |
Affected |
| Microsoft |
Windows 7 Service Pack 1
|
6.1.0 to < 1.001 |
Affected |
| Microsoft |
Windows 7 Service Pack 1
|
6.1.0 to < 6.1.7601.26221 |
Affected |
| Microsoft |
Windows 8.1
|
6.3.0 to < 6.3.9600.20120 |
Affected |
| Microsoft |
Windows 8.1
|
6.3.0 to < 1.001 |
Affected |
| Microsoft |
Windows Server 2008 Service Pack 2
|
6.0.0 to < 6.0.6003.21218 |
Affected |
| Microsoft |
Windows Server 2008 Service Pack 2
|
6.0.0 to < 1.001 |
Affected |
| Microsoft |
Windows Server 2008 Service Pack 2 (Server Core installation)
|
6.0.0 to < 6.0.6003.21218 |
Affected |
CVE References
- portal.msrc.microsoft.com/en-US/security-guidance/advisory/CVE-2021-40444 portal.msrc.microsoft.com · CVE Record https://portal.msrc.microsoft.com/en-US/security-guidance/advisory/CV...
- packetstormsecurity.com/files/164210/Microsoft-Windows-MSHTML-Overvi... packetstormsecurity.com · CVE Record http://packetstormsecurity.com/files/164210/Microsoft-Windows-MSHTML-...
- packetstormsecurity.com/files/165214/Microsoft-Office-Word-MSHTML-Re... packetstormsecurity.com · CVE Record http://packetstormsecurity.com/files/165214/Microsoft-Office-Word-MSH...
- packetstormsecurity.com/files/167317/Microsoft-Office-MSDT-Follina-P... packetstormsecurity.com · CVE Record http://packetstormsecurity.com/files/167317/Microsoft-Office-MSDT-Fol...
Recommended Actions
- Prioritize remediation. Validate affected assets and apply vendor fixes on an accelerated timeline.
- Check enrichment artifacts for scanner coverage and available PoCs before rolling remediation validation.
- Use the Pro API to automate enrichment, telemetry, and workflow delivery for VM, SOC, and CTI pipelines.
Known Exploited Vulnerability Sources
Catalogues that list this CVE as a known exploited vulnerability.
Per-source evidence links for KEV attestations are available through the KEVIntel Pro API.
Learn about Pro API access| Source | Added |
|---|---|
| CISA First | 2021-11-03 00:00 UTC |
Scanner Artifacts
Nuclei and Metasploit references linked to this CVE.
| Scanner | Reference | Detected |
|---|---|---|
| Metasploit | https://github.com/rapid7/metasploit-framework/blob/master/modules/exploits/windows/fileformat/word_mshtml_rce.rb | Apr 28, 2025 |
Virtual Patch
Compensating WAF rules to help reduce exposure to this CVE. Rule content and deployable vendor exports are available with KEVIntel Enterprise.
KEVIntel does not currently have a virtual patch for this CVE. When available, KEVIntel virtual patches ship as deployable ModSecurity, Cloudflare, and AWS WAF rules.
Enterprise feature. Virtual patch rule content and deployable vendor exports (ModSecurity, Cloudflare, AWS WAF) are available to KEVIntel Enterprise users.
CVSS Scores
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:H/A:L/E:P/RL:O/RC:C
Exploitation Status
Exploited in the wild
Recorded 2021-11-03 00:00:00 UTC · CISA
Used in malware
Recorded 2021-11-03 00:00:00 UTC · CISA
Proof of concept available
Recorded 2021-09-08 08:32:40 UTC · GitHub
Weaknesses (CWE)
-
Improper Limitation of a Pathname to a Restricted Directory ('Path Traversal')
Scanner Integrations
| Scanner | Reference | Detected |
|---|---|---|
| Metasploit | https://github.com/rapid7/metasploit-framework/blob/master/modules/exploits/windows/fileformat/word_mshtml_rce.rb | Apr 28, 2025 |
Potential Proof of Concepts
These PoCs are unverified and could contain malware. Use at your own risk.
github · Created 2024-07-28 17:23:43 UTC · 0 stars
This repository contains scripts and resources for exploiting the Follina CVE and CVE-2021-40444 vulnerabilities in Microsoft Office. The scripts generate malicious document files that can execute arbitrary code on the target system.
github · Created 2021-12-28 06:33:25 UTC · 2 stars
Microsoft-Office-Word-MSHTML-Remote-Code-Execution-Exploit
github · Created 2021-10-28 14:55:46 UTC · 8 stars
An attempt to reproduce Microsoft MSHTML Remote Code Execution (RCE) Vulnerability and using Metasploit Framework.
github · Created 2021-10-03 01:13:42 UTC · 9 stars
github · Created 2021-09-19 19:46:28 UTC · 101 stars
Modified code so that we don´t need to rely on CAB archives
github · Created 2021-09-16 10:32:23 UTC · 0 stars
CVE-2021-40444 - Custom CAB templates from MakeCAB
github · Created 2021-09-15 22:34:35 UTC · 810 stars
CVE-2021-40444 - Fully Weaponized Microsoft Office Word RCE Exploit
github · Created 2021-09-14 17:10:48 UTC · 19 stars
github · Created 2021-09-12 18:05:53 UTC · 171 stars
This repo contain builders of cab file, html file, and docx file for CVE-2021-40444 exploit
github · Created 2021-09-11 02:49:37 UTC · 4 stars
github · Created 2021-09-09 23:41:52 UTC · 3 stars
github · Created 2021-09-09 03:15:57 UTC · 14 stars
github · Created 2021-09-08 08:32:40 UTC · 17 stars
Microsoft MSHTML Remote Code Execution Vulnerability CVE-2021-40444
Timeline
Key exploitation, disclosure, scanner coverage, and KEV attestation events for this CVE.
-
15:02 UTC about 1 year ago15:02 UTC · about 1 year ago
Metasploit module available
Exploit module available
-
00:00 UTC over 4 years ago00:00 UTC · over 4 years ago
Added to CISA KEV
Listed in the CISA Known Exploited Vulnerabilities catalog
-
00:00 UTC over 4 years ago00:00 UTC · over 4 years ago
First public exploitation report
Exploit observed in malware
-
11:24 UTC almost 5 years ago11:24 UTC · almost 5 years ago
CVE published
Vulnerability disclosed publicly
-
08:32 UTC almost 5 years ago08:32 UTC · almost 5 years ago
Public PoC available
Public proof-of-concept code published
-
00:00 UTC almost 5 years ago00:00 UTC · almost 5 years ago
CVE ID reserved
Identifier reserved by the CNA
Automate This Intelligence with the Pro API
Confidence scoring, exploit status, sensor telemetry, PoCs, scanner integrations, mentions, and tags are available programmatically for VM, SOC, and CTI workflows.
Pro API Example
GET /api/v2/pro/kevs/CVE-2021-40444
{
"cve_id": "CVE-2021-40444",
"title": "Microsoft MSHTML Remote Code Execution Vulnerability",
"affected_vendor": "Microsoft",
"affected_product": "Windows 10 Version 1809, Windows Server 2019, Windows Server 2019 (Server Core installation), Windows 10 Version 1909, Windows 10 Version 21H1, Windows Server 2022, Windows 10 Version 2004, Windows Server version 2004, Windows 10 Version 20H2, Windows Server version 20H2, Windows 10 Version 1507, Windows 10 Version 1607, Windows Server 2016, Windows Server 2016 (Server Core installation), Windows 7, Windows 7 Service Pack 1, Windows 8.1, Windows Server 2008 Service Pack 2, Windows Server 2008 Service Pack 2 (Server Core installation), Windows Server 2008 Service Pack 2, Windows Server 2008 R2 Service Pack 1, Windows Server 2008 R2 Service Pack 1 (Server Core installation), Windows Server 2012, Windows Server 2012 (Server Core installation), Windows Server 2012 R2, Windows Server 2012 R2 (Server Core installation)",
"affected_versions": [
{ "vendor": "...", "product": "...", "status": "affected", "display_label": "..." }
],
"confidence": "Confirmed",
"cvss_score": 8.8,
"epss_score": null,
"exploit_status": {
"exploited_in_the_wild": true,
"active_exploitation_observed": false
},
"sensor_telemetry": { "...": "Pro API fields" },
"proof_of_concepts": [ "..." ],
"scanner_integrations": [ "..." ]
}