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Windows 10 21h2Operating system · Microsoft

CVE-2026-20842

HIGH · 7.0 CVSS v3.1 Published 2026-01-13
Fix available
A fix is available. Upgrade to 10.0.19044.6809 / 10.0.19045.6809 or later.
See remediation →
72/100
Remediation priority · Elevated
Zero-click

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
Use after free in Windows DWM allows an authorized attacker to elevate privileges locally.

In the news

Third-party coverage
Trending covered by 1 outlet this week · latest 7mo ago

Surfaced from public web coverage — external links open in a new tab.

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

A use-after-free vulnerability exists in the Windows Desktop Window Manager (DWM) that allows a locally authorized attacker to elevate privileges to higher integrity levels by exploiting improper memory management in the DWM process.

MitigationApply Microsoft security updates for CVE-2026-20842 once released; prioritize workstations and servers with interactive users. Monitor for anomalous DWM process behavior as a defense-in-depth measure.

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 21h2Operating system
Affected:< 10.0.19044.6809
Windows 10 22h2Operating system
Affected:< 10.0.19045.6809
Windows 11 23h2Operating system
Affected:< 10.0.22631.6491
Windows 11 24h2Operating system
Affected:< 10.0.26100.7623
Windows 11 25h2Operating system
Affected:< 10.0.26200.7623
Windows Server 2022Operating system
Affected:< 10.0.20348.4648
Windows Server 2022 23h2Operating system
Affected:< 10.0.25398.2092
Windows Server 2025Operating system
Affected:< 10.0.26100.32230

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
Local
Complexity
High
Privileges
Low
User interaction
None
Scope
Unchanged
Confidentiality
High
Integrity
High
Availability
High

CVSS:3.1/AV:L/AC:H/PR:L/UI:N/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. Check Windows 10 21h2 build number
    Run `winver` or `systeminfo | findstr /B /C:"OS Version"` and note the build number (e.g., 10.0.19044.xxxx)
    Affected if Build is lower than 10.0.19044.6809
  2. Check Windows 10 22h2 build number
    Run `winver` or `systeminfo | findstr /B /C:"OS Version"` and note the build number (e.g., 10.0.19045.xxxx)
    Affected if Build is lower than 10.0.19045.6809
  3. Check Windows 11 23h2 build number
    Run `winver` or `systeminfo | findstr /B /C:"OS Version"` and note the build number (e.g., 10.0.22631.xxxx)
    Affected if Build is lower than 10.0.22631.6491
  4. Check Windows 11 24h2 or 25h2 build number
    Run `winver` or `systeminfo | findstr /B /C:"OS Version"` and note the build number (e.g., 10.0.26100.xxxx or 10.0.26200.xxxx)
    Affected if Build is lower than 10.0.26100.7623 (24h2) or 10.0.26200.7623 (25h2)
  5. Check Windows Server build number
    Run `systeminfo` and note the OS Version build (e.g., 10.0.20348.xxxx or 10.0.25398.xxxx)
    Affected if Build is lower than 10.0.20348.4648 (Server 2022), 10.0.25398.2092 (Server 2022 23h2), or 10.0.26100.32230 (Server 2025)
  6. Confirm DWM process is present
    Run `tasklist /FI "IMAGENAME eq dwm.exe"` to verify the Desktop Window Manager is running
    Affected if DWM is running (required for the vulnerability to be exploitable)

You are affected if your Windows or Windows Server build number falls below the specified thresholds AND your system has the DWM process running.

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 10.0.19044.6809 / 10.0.19045.6809 / 10.0.20348.4648 or later
Fixed in 10.0.19044.680910.0.19045.680910.0.20348.4648
Interim mitigation

Apply Microsoft security updates for CVE-2026-20842 once released; prioritize workstations and servers with interactive users. Monitor for anomalous DWM process behavior as a defense-in-depth measure.

Recommended fix High confidence

Upgrade to the latest Windows security update that includes the fix for this DWM Use After Free vulnerability. Specific fixed builds: Windows 10 21h2 (10.0.19044.6809+), Windows 10 22h2 (10.0.19045.6809+), Windows 11 23h2 (10.0.22631.6491+), Windows 11 24h2 (10.0.26100.7623+), Windows 11 25h2 (10.0.

  1. 1. Identify the current Windows version by running 'winver' or checking System Properties
  2. 2. Determine which Windows release version you are running (21h2, 22h2, 23h2, 24h2, 25h2, Server 2022, Server 2022 23h2, or Server 2025)
  3. 3. Open Windows Settings and navigate to Windows Update, or run 'ms-settings:windowsupdate'
  4. 4. Click 'Check for updates' to download and install the latest security updates
  5. 5. Ensure the installed build number meets or exceeds the fixed version for your release: Windows 10 21h2 requires 10.0.19044.6809+, Windows 10 22h2 requires 10.0.19045.6809+, Windows 11 23h2 requires 10.0.22631.6491+, Windows 11 24h2 requires 10.0.26100.7623+, Windows 11 25h2 requires 10.0.26200.7623+, Windows Server 2022 requires 10.0.20348.4648+, Windows Server 2022 23h2 requires 10.0.25398.209
  6. 6. Restart the system when prompted to complete the update installation
  7. 7. Verify the fix by confirming the build number matches or exceeds the required version using 'winver'
Caveat Standard Windows security update risks apply - updates may require system restart and should be tested in non-production environments first

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

Fix this in Windows 10 21h2 Scoped from the published advisory
  • Consultation3.0 h
  • Implementation4.0 h
  • Testing2.0 h
  • Review / QA2.0 h
11.0 hours of engineering $1,980
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Scan for this in your stack

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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-2026-20842 in production — separate from our analysis above.

No notes yet

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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