Evidence dossier

CVE-2021-40444

Microsoft MSHTML Remote Code Execution Vulnerability

76.796.7Priority evidence range
As known Jul 19, 2026, 5:00 AM UTCgen-56ccdaf9

Normalized restatement

<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>

State
PUBLISHED
Published
Sep 15, 2021
Updated
Mar 11, 2026
Evidence coverage
72%
CISA KEVCatalog member

Apply updates per vendor instructions.

FIRST EPSS96.84%

2026-07-18 · v2026.06.15 · percentile 99.9%

Source stateConflict visible

Distinct CVSS assessments remain side by side; none are averaged.

Source comparison

Who said what

CISA-ADPindependent enrichment
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CISA ADP Vulnrichment

CVEderivative copy
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CVE Program Container

microsoftoriginal assertion
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Microsoft MSHTML Remote Code Execution Vulnerability

CISA KEVoriginal assertion
observed_exploitation

Microsoft MSHTML Remote Code Execution Vulnerability

FIRST EPSSoriginal assertion
model_probability

Probability 0.968430000000; percentile 0.998820000000

Applicability

Cited product scope

Trace impact →
MicrosoftWindows 10 Version 1507
[{"status": "affected", "version": "10.0.0", "lessThan": "10.0.10240.19060", "versionType": "custom"}]unknown
MicrosoftWindows 10 Version 1607
[{"status": "affected", "version": "10.0.0", "lessThan": "10.0.14393.4651", "versionType": "custom"}]unknown
MicrosoftWindows 10 Version 1809
[{"status": "affected", "version": "10.0.0", "lessThan": "10.0.17763.2183", "versionType": "custom"}]unknown
MicrosoftWindows 10 Version 1909
[{"status": "affected", "version": "10.0.0", "lessThan": "10.0.18363.1801", "versionType": "custom"}]unknown
MicrosoftWindows 10 Version 2004
[{"status": "affected", "version": "10.0.0", "lessThan": "10.0.19041.1237", "versionType": "custom"}]unknown
MicrosoftWindows 10 Version 20H2
[{"status": "affected", "version": "10.0.0", "lessThan": "10.0.19042.1237", "versionType": "custom"}]unknown
MicrosoftWindows 10 Version 21H1
[{"status": "affected", "version": "10.0.0", "lessThan": "10.0.19043.1237", "versionType": "custom"}]unknown
MicrosoftWindows 7
[{"status": "affected", "version": "6.1.0", "lessThan": "6.1.7601.25712", "versionType": "custom"}, {"status": "affected", "version": "6.1.0", "lessThan": "1.001", "versionType": "custom"}, {"status": "affected", "version": "6.1.0", "lessThan": "6.1.7601.26221", "versionType": "custom"}]unknown
MicrosoftWindows 7 Service Pack 1
[{"status": "affected", "version": "6.1.0", "lessThan": "6.1.7601.25712", "versionType": "custom"}, {"status": "affected", "version": "6.1.0", "lessThan": "1.001", "versionType": "custom"}, {"status": "affected", "version": "6.1.0", "lessThan": "6.1.7601.26221", "versionType": "custom"}]unknown
MicrosoftWindows 8.1
[{"status": "affected", "version": "6.3.0", "lessThan": "6.3.9600.20120", "versionType": "custom"}, {"status": "affected", "version": "6.3.0", "lessThan": "1.001", "versionType": "custom"}]unknown
MicrosoftWindows Server 2008 R2 Service Pack 1
[{"status": "affected", "version": "6.1.0", "lessThan": "6.1.7601.25712", "versionType": "custom"}, {"status": "affected", "version": "6.1.0", "lessThan": "1.001", "versionType": "custom"}]unknown
MicrosoftWindows Server 2008 R2 Service Pack 1 (Server Core installation)
[{"status": "affected", "version": "6.0.0", "lessThan": "6.1.7601.25712", "versionType": "custom"}, {"status": "affected", "version": "6.0.0", "lessThan": "1.001", "versionType": "custom"}]unknown
MicrosoftWindows Server 2008 Service Pack 2
[{"status": "affected", "version": "6.0.0", "lessThan": "6.0.6003.21218", "versionType": "custom"}, {"status": "affected", "version": "6.0.0", "lessThan": "1.001", "versionType": "custom"}]unknown
MicrosoftWindows Server 2008 Service Pack 2
[{"status": "affected", "version": "6.0.0", "lessThan": "6.0.6003.21218", "versionType": "custom"}, {"status": "affected", "version": "6.0.0", "lessThan": "1.001", "versionType": "custom"}]unknown
MicrosoftWindows Server 2008 Service Pack 2 (Server Core installation)
[{"status": "affected", "version": "6.0.0", "lessThan": "6.0.6003.21218", "versionType": "custom"}, {"status": "affected", "version": "6.0.0", "lessThan": "1.001", "versionType": "custom"}]unknown
MicrosoftWindows Server 2012
[{"status": "affected", "version": "6.2.0", "lessThan": "6.2.9200.23462", "versionType": "custom"}, {"status": "affected", "version": "6.2.0", "lessThan": "1.001", "versionType": "custom"}]unknown
MicrosoftWindows Server 2012 R2
[{"status": "affected", "version": "6.3.0", "lessThan": "6.3.9600.20120", "versionType": "custom"}, {"status": "affected", "version": "6.3.0", "lessThan": "1.001", "versionType": "custom"}]unknown
MicrosoftWindows Server 2012 R2 (Server Core installation)
[{"status": "affected", "version": "6.3.0", "lessThan": "6.3.9600.20120", "versionType": "custom"}, {"status": "affected", "version": "6.3.0", "lessThan": "1.001", "versionType": "custom"}]unknown
MicrosoftWindows Server 2012 (Server Core installation)
[{"status": "affected", "version": "6.2.0", "lessThan": "6.2.9200.23462", "versionType": "custom"}, {"status": "affected", "version": "6.2.0", "lessThan": "1.001", "versionType": "custom"}]unknown
MicrosoftWindows Server 2016
[{"status": "affected", "version": "10.0.0", "lessThan": "10.0.14393.4651", "versionType": "custom"}]unknown
MicrosoftWindows Server 2016 (Server Core installation)
[{"status": "affected", "version": "10.0.0", "lessThan": "10.0.14393.4651", "versionType": "custom"}]unknown
MicrosoftWindows Server 2019
[{"status": "affected", "version": "10.0.0", "lessThan": "10.0.17763.2183", "versionType": "custom"}]unknown
MicrosoftWindows Server 2019 (Server Core installation)
[{"status": "affected", "version": "10.0.0", "lessThan": "10.0.17763.2183", "versionType": "custom"}]unknown
MicrosoftWindows Server 2022
[{"status": "affected", "version": "10.0.0", "lessThan": "10.0.20348.230", "versionType": "custom"}]unknown
MicrosoftWindows Server version 2004
[{"status": "affected", "version": "10.0.0", "lessThan": "10.0.19041.1237", "versionType": "custom"}]unknown
MicrosoftWindows Server version 20H2
[{"status": "affected", "version": "10.0.0", "lessThan": "10.0.19042.1237", "versionType": "custom"}]unknown
Unknown vendorUnknown product
cpe:2.3:o:microsoft:windows_10_1507:*:*:*:*:*:*:*:*; end excluding 10.0.10240.19060supported
Unknown vendorUnknown product
cpe:2.3:o:microsoft:windows_10_1607:*:*:*:*:*:*:*:*; end excluding 10.0.14393.4651supported
Unknown vendorUnknown product
cpe:2.3:o:microsoft:windows_10_1809:*:*:*:*:*:*:*:*; end excluding 10.0.17763.2183supported
Unknown vendorUnknown product
cpe:2.3:o:microsoft:windows_10_1909:*:*:*:*:*:*:*:*; end excluding 10.0.18363.1801supported
Unknown vendorUnknown product
cpe:2.3:o:microsoft:windows_10_2004:*:*:*:*:*:*:*:*; end excluding 10.0.19041.1237supported
Unknown vendorUnknown product
cpe:2.3:o:microsoft:windows_10_20h2:*:*:*:*:*:*:*:*; end excluding 10.0.19042.1237supported
Unknown vendorUnknown product
cpe:2.3:o:microsoft:windows_10_21h1:*:*:*:*:*:*:*:*; end excluding 10.0.19043.1237supported
Unknown vendorUnknown product
cpe:2.3:o:microsoft:windows_7:-:sp1:*:*:*:*:*:*supported
Unknown vendorUnknown product
cpe:2.3:o:microsoft:windows_8.1:-:*:*:*:*:*:*:*supported
Unknown vendorUnknown product
cpe:2.3:o:microsoft:windows_rt_8.1:-:*:*:*:*:*:*:*supported
Unknown vendorUnknown product
cpe:2.3:o:microsoft:windows_server_2004:*:*:*:*:*:*:*:*; end excluding 10.0.19041.1237supported
Unknown vendorUnknown product
cpe:2.3:o:microsoft:windows_server_2008:r2:sp1:*:*:*:*:x64:*supported
Unknown vendorUnknown product
cpe:2.3:o:microsoft:windows_server_2008:-:sp2:*:*:*:*:*:*supported
Unknown vendorUnknown product
cpe:2.3:o:microsoft:windows_server_2012:-:*:*:*:*:*:*:*supported
Unknown vendorUnknown product
cpe:2.3:o:microsoft:windows_server_2012:-:r2:*:*:*:*:*:*supported
Unknown vendorUnknown product
cpe:2.3:o:microsoft:windows_server_2016:*:*:*:*:*:*:*:*; end excluding 10.0.14393.4651supported
Unknown vendorUnknown product
cpe:2.3:o:microsoft:windows_server_2019:*:*:*:*:*:*:*:*; end excluding 10.0.17763.2183supported
Unknown vendorUnknown product
cpe:2.3:o:microsoft:windows_server_2022:*:*:*:*:*:*:*:*; end excluding 10.0.20348.230supported
Unknown vendorUnknown product
cpe:2.3:o:microsoft:windows_server_20h2:*:*:*:*:*:*:*:*; end excluding 10.0.19042.1237supported

Assessments

CVSS by origin

6.8
nvd@nist.govCVSS 2.0 · role PrimaryAV:N/AC:M/Au:N/C:P/I:P/A:P
7.8
nvd@nist.govCVSS 3.1 · role SecondaryCVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H
8.8
secure@microsoft.comCVSS 3.1 · role SecondaryCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:H/A:L
8.8
microsoftCVSS 3.1 · role unknownCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:H/A:L/E:P/RL:O/RC:C

Limitations and unknowns

  • KEV membership is authoritative for the catalog, not proof of exposure in any environment.
  • EPSS is a dated model probability and not an individual-environment prediction.
  • Affected or fixed status applies only to the exact cited product and version scope; unresolved scope remains unknown.
  • NVD-carried upstream facts remain derivative and are not independent corroboration.
  • Only NVD metrics validated under the generation-bound calculator are Public Priority eligible; direct CVE record metrics remain display-only.
  • NVD CVSS source eligibility is closed: NVD-authored, exact record-source, or registered same-CVE container origin; unmapped sources remain display-only.
  • Factor D is unknown in Public Core because no accepted canonical mapping-obligation ledger is present.
  • Core replay supports the active and immediately prior generation; retrospective valid-at replay is deferred.