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Actively exploited in the wild. This CVE is on the CISA Known Exploited Vulnerabilities list — treat remediation as urgent. Federal remediation due by 17 Nov 2021.
Windows 10 1507Operating system · Microsoft

CVE-2021-33742

HIGH · 7.5 CVSS v3.1 Published 2021-06-08
Fix available
A fix is available. Upgrade to 10.0.10240.18967 / 10.0.14393.4467 or later.
See remediation →
100/100
Remediation priority · Urgent
In the wild High EPSS Remotely reachable No privileges Patch available

Official description Straight from the sourceThe vendor's or NVD's own wording, published unedited. Authoritative, but often terse — it says what broke, rarely what to do.

NVD · unedited
Windows MSHTML Platform Remote Code Execution Vulnerability

Technical summary Written by usOur analysis, written from the advisory, the CVSS vector and the affected-version data. It adds context the advisory leaves out, and never invents facts that are not in the source.

dbcve analysis · moderate confidence

This is a Remote Code Execution vulnerability in the Windows MSHTML platform (the rendering engine also known as Trident, used by Internet Explorer and embedded in certain Windows components). The 7.5 CVSS indicates it can be exploited remotely without authentication to execute arbitrary code.

MitigationApply the Microsoft security update KB5003635 (or subsequent relevant patch) for CVE-2021-33742, or disable/limit MSHTML/Internet Explorer rendering components in enterprise environments where feasible.

Verify against the referenced sources before acting — the references below are authoritative for this CVE, this summary is not.

Affected products & versions What the vendor confirmedThe version ranges the vendor confirmed as vulnerable. If your version sits inside a range here, treat yourself as exposed until you have upgraded.

NVD · CPE data
Windows 10 1507Operating system
Affected:< 10.0.10240.18967
Windows 10 1607Operating system
Affected:< 10.0.14393.4467
Windows 10 1809Operating system
Affected:< 10.0.17763.1999
Windows 10 1909Operating system
Affected:< 10.0.18363.1621
Windows 10 2004Operating system
Affected:< 10.0.19041.1052
Windows 10 20h2Operating system
Affected:< 10.0.19042.1052
Windows 10 21h1Operating system
Affected:< 10.0.19043.1052
Windows 7Operating system
Affected:all versions

CVSS breakdown How the score is builtThe industry scoring standard. It rates how the flaw is reached, what it takes to exploit, and what an attacker gains — the score is derived from those, not the other way round.

From the vector
Attack vector
Network
Complexity
High
Privileges
None
User interaction
Required
Scope
Unchanged
Confidentiality
High
Integrity
High
Availability
High

CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:U/C:H/I:H/A:H

Am I affected? How to checkSteps we derive from the advisory and the affected-version data, so you can decide whether this CVE reaches your setup. They are a guide, not a scan — your own configuration is the authority.

dbcve checks

Work through these to decide whether this CVE applies to you.

  1. Identify Windows version and build number
    Run 'winver' or 'systeminfo | findstr /B /C:"OS Name" /C:"OS Version"' to get the Windows version and build number
    Affected if The build number is below the threshold for your Windows 10 version (1507:<18967, 1607:<4467, 1809:<1999, 1909:<1621, 2004:<1052, 20h2:<1052, 21h1:<1052) OR the system is Windows 7 (any build)
  2. Confirm Internet Explorer or MSHTML is enabled
    Check registry key HKLM\SOFTWARE\Policies\Microsoft\Windows\CurrentVersion\Internet Settings or use 'Get-WindowsOptionalFeature -Online -FeatureName *InternetExplorer*' in PowerShell to see if IE is installed/enabled
    Affected if Internet Explorer feature is installed and enabled (the vulnerability requires MSHTML parsing to be accessible)
  3. Verify mshtml.dll version
    Check the mshtml.dll file version at C:\Windows\System32\mshtml.dll by right-clicking the file > Properties > Details, or run 'powershell (Get-Item C:\Windows\System32\mshtml.dll).VersionInfo.FileVersion'
    Affected if The file version is lower than the patched versions for your Windows build (the vulnerability exists in unpatched mshtml.dll)

Your system is affected if it runs an unpatched Windows 7 (any version) or Windows 10 build below the thresholds listed, AND Internet Explorer or MSHTML-based components are enabled on the system.

Generated from the published advisory. Verify against your own configuration.

Check your environment

Paste your version and any relevant configuration and it will be compared against the affected criteria above. Do not include secrets or credentials.

AI-assisted, checked against the advisory. Informational, not a guarantee.

Remediation Closing itWhat it takes to close this. Where a vendor fix exists we point at it; where none exists we say so plainly, and can build one. Effort estimates are scoped from the advisory, not from your codebase.

dbcve · scoped
Upgrade available Upgrade to 10.0.10240.18967 / 10.0.14393.4467 / 10.0.17763.1999 or later
Fixed in 10.0.10240.1896710.0.14393.446710.0.17763.1999
Vendor patch portal.msrc.microsoft.com →
Interim mitigation

Apply the Microsoft security update KB5003635 (or subsequent relevant patch) for CVE-2021-33742, or disable/limit MSHTML/Internet Explorer rendering components in enterprise environments where feasible.

Recommended fix High confidence

Apply KB5003690 or later cumulative update for your specific Windows 10 version (1507: build 10240.18967+, 1607: build 14393.4467+, 1809: build 17763.1999+, 1909: build 18363.1621+, 2004: build 19041.1052+, 20h2: build 19042.1052+, 21h1: build 19043.1052+)

  1. Open Windows Update settings on the affected system
  2. Check for and install all available Windows security updates
  3. Verify the installed build version matches or exceeds the minimum fixed version for your Windows 10 release
  4. For Windows 7 systems: this version is end-of-life with no security updates; migrate to a supported Windows version or implement compensating controls such as disabling MSHTML scripting or using alternative browsers
Caveat Standard Windows update process; minimal risk; Windows 7 has no security patch available

Generated from the published advisory — verify against the referenced sources before acting.

Fix this in Windows 10 1507 Exploited in the wild — priority engagement
  • Consultation2.0 h
  • Implementation4.0 h
  • Testing3.0 h
  • Review / QA2.0 h
11.0 hours of engineering $1,930
Get it fixed fast

An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $3,088.

Scan for this in your stack

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dbcve dependency scanner

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References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.

Primary sources

Practitioner notes

Contributed

Peer-ranked notes from engineers who’ve handled CVE-2021-33742 in production — separate from our analysis above.

No notes yet

Be the first to add a field note for this CVE — a mitigation you’ve verified, a version caveat, or a link to a working fix. Sign in above to contribute.

What this is

A place for practitioners to share what actually worked: a mitigation you’ve tested, a configuration change, a version- or environment-specific caveat, or a link to a verified patch. The most useful notes rise to the top as peers upvote them, so the signal stays high.

What belongs here
  • Verified mitigations, workarounds, and config changes
  • Version or environment caveats, and links to real fixes
  • No weaponised exploit code, or anything meant to cause harm
  • No spam, self-promotion, credentials, or personal data