Vulnerability record

CVE-2021-33742

Microsoft Windows MSHTML Platform Remote Code Execution Vulnerability

HighExploitation confirmedCISA KEV

What should I do?

This vulnerability is in the CISA Known Exploited Vulnerabilities catalog: attackers are using it. If you run Windows, fix it now.

CISA required action: Apply updates per vendor instructions.

US federal civilian agencies must remediate by Nov 17, 2021.

Patch status

Official fix available since Sep 30, 2026

Apply the vendor's update to every affected system. Check the fixed-in versions below where known.

Basis: NVD patch reference

Windows MSHTML Platform Remote Code Execution Vulnerability

Source: NIST National Vulnerability Database. Official vulnerability data, reproduced as published.

Products affected by this vulnerability, with versions and the source of each entry
Product	Vendor	Source
Windows	Microsoft	KEV

Sources: KEV = CISA Known Exploited Vulnerabilities catalog. Version details have not been published yet.

Developments from the last 30 days, newest first.

CVSS scoredUpdateKEVSep 30, 2026
CVE-2021-33742 scored CVSS 7.5: Microsoft Windows, Microsoft Windows MSHTML Platform Remote Code Execution Vulnerability
CISA lists this as exploited in the wild. Unpatched Windows systems are exposed to active attacks now.
Basis: NIST National Vulnerability Database
Patch releasedUpdateKEVSep 30, 2026
Patch released for CVE-2021-33742: Microsoft Windows, Microsoft Windows MSHTML Platform Remote Code Execution Vulnerability
An official fix is now available for Microsoft Windows. This vulnerability is being exploited, so apply it promptly.
Basis: NVD patch reference

1 earlier event is available with a subscription. See plans.

We have not published a story about this vulnerability yet.

nvd.nist.gov https://nvd.nist.gov/vuln/detail/CVE-2021-33742
portal.msrc.microsoft.com https://portal.msrc.microsoft.com/en-US/security-guidance/advisory/CVE-2021-33742
cisa.gov https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2021-33742