CVE record · CVE-2021-40444

Microsoft MSHTML Remote Code Execution Vulnerability

CVSS 8.8 HighCriticalIn CISA KEV · ransomwareEPSS 0.98 · 99th percentile

Critical, because:

In CISA’s KEV catalogue since 3 Nov 2021: it is known to be exploited.
CVSS score 8.8 (7.0 or more) and EPSS 0.98 (0.1 or more): a high score and a real chance of exploitation in the next 30 days.

Published by the CVE Program (CNA: microsoft) at 15 Sept 2021, 11:24 UTC. agentprime has not analysed this yet, so whether it affects any app is not known. This CVE names a vendor and product rather than a package, so the lockfile check doesn’t match it.

Affected products, as the CNA wrote them
Vendor	Product	Versions
Microsoft	Windows 10 Version 1507	affected 10.0.10240.0 to before 10.0.10240.19060 custom
Microsoft	Windows 10 Version 1607	affected 10.0.14393.0 to before 10.0.14393.4651 custom
Microsoft	Windows 10 Version 1809	affected 10.0.17763.0 to before 10.0.17763.2183 custom
Microsoft	Windows 10 Version 1809	affected 10.0.0 to before 10.0.17763.2183 custom
Microsoft	Windows 10 Version 1909	affected 10.0.0 to before 10.0.18363.1801 custom
Microsoft	Windows 10 Version 2004	affected 10.0.0 to before 10.0.19041.1237 custom
Microsoft	Windows 10 Version 20H2	affected 10.0.0 to before 10.0.19042.1237 custom
Microsoft	Windows 10 Version 21H1	affected 10.0.0 to before 10.0.19043.1237 custom
Microsoft	Windows 7	affected 6.1.0 to before 6.1.7601.25712 custom
Microsoft	Windows 7 Service Pack 1	affected 6.1.0 to before 6.1.7601.25712 custom
Microsoft	Windows 8.1	affected 6.3.0 to before 6.3.9600.20120 custom
Microsoft	Windows Server 2008 R2 Service Pack 1	affected 6.1.7601.0 to before 6.1.7601.25712 custom
Microsoft	Windows Server 2008 R2 Service Pack 1 (Server Core installation)	affected 6.1.7601.0 to before 6.1.7601.25712 custom
Microsoft	Windows Server 2008 Service Pack 2	affected 6.0.6003.0 to before 6.0.6003.21218 custom
Microsoft	Windows Server 2008 Service Pack 2 (Server Core installation)	affected 6.0.6003.0 to before 6.0.6003.21218 custom
Microsoft	Windows Server 2012	affected 6.2.9200.0 to before 6.2.9200.23462 custom
Microsoft	Windows Server 2012 (Server Core installation)	affected 6.2.9200.0 to before 6.2.9200.23462 custom
Microsoft	Windows Server 2012 R2	affected 6.3.9600.0 to before 6.3.9600.20120 custom
Microsoft	Windows Server 2012 R2 (Server Core installation)	affected 6.3.9600.0 to before 6.3.9600.20120 custom
Microsoft	Windows Server 2016	affected 10.0.14393.0 to before 10.0.14393.4651 custom
Microsoft	Windows Server 2016 (Server Core installation)	affected 10.0.14393.0 to before 10.0.14393.4651 custom
Microsoft	Windows Server 2019	affected 10.0.17763.0 to before 10.0.17763.2183 custom
Microsoft	Windows Server 2019 (Server Core installation)	affected 10.0.17763.0 to before 10.0.17763.2183 custom
Microsoft	Windows Server 2022	affected 10.0.20348.0 to before 10.0.20348.230 custom
Microsoft	Windows Server version 2004	affected 10.0.0 to before 10.0.19041.1237 custom
Microsoft	Windows Server version 20H2	affected 10.0.0 to before 10.0.19042.1237 custom

Identifiers: CVE-2021-40444
CNA: microsoft
Weakness (CWE): CWE-22
Tags: Microsoft Windows 10 Version 1507
Microsoft Windows 10 Version 1607
Microsoft Windows 10 Version 1809
Microsoft Windows 10 Version 1909
Microsoft Windows 10 Version 2004
Microsoft Windows 10 Version 20H2
Microsoft Windows 10 Version 21H1
Microsoft Windows 7
Path traversal
Published: 15 Sept 2021
Updated: 10 Aug 2026

Not analysed yet

We haven’t published our own analysis of this CVE. If a person reviews it, this page will say what’s affected and what has to be true for it to matter.

Severity and exploitation

Score	Rating	CVSS	Vector	Source
8.8	High	3.1	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	CNA (microsoft)

CISA KEV Listed since 3 Nov 2021: known to be exploited. CISA reports use in ransomware campaigns.
EPSS 0.98, the 99th percentile, on 5 Nov 2026: FIRST’s estimate of the chance of exploitation in the next 30 days.

Timeline

This record came from the full history of the CVE Program, published 15 Sept 2021. New records show when each source confirmed them.

Sources

References from the CNA

msrc.microsoft.com/update-guide/vulnerability/CVE-2021-40444 vendor-advisorypatch

Facts on this page come from the CVE List as the CNA published them, with CVSS from the sources named above, CISA KEV and FIRST EPSS. Vendors, products and versions are shown as the CNA wrote them. We don’t reproduce the CVE’s description.