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Windows 10 21h2Operating system · Microsoft

CVE-2026-20871

HIGH · 7.8 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 →
80/100
Remediation priority · High
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 Desktop Windows Manager allows an authorized attacker to elevate privileges locally.

In the news

Third-party coverage
Trending covered by 2 outlets 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 in the Desktop Windows Manager (DWM) enables a locally authenticated attacker to elevate privileges to higher permission levels. The vulnerability stems from improper memory management in DWM, a core Windows system process responsible for rendering the desktop environment.

MitigationApply available security patches for this vulnerability immediately. Restrict local administrative access and monitor for suspicious processes interacting with DWM. Consider disabling unnecessary DWM extensions or third-party visual themes until patch deployment.

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

CVSS:3.1/AV:L/AC:L/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 installed Windows version
    Run 'winver' from command prompt or 'systeminfo' and look at OS Version / OS Name and Build Number
    Affected if Build number is less than the affected threshold for your Windows version (19044.6809 for 21h2, 19045.6809 for 22h2, 22631.6491 for 11 23h2, 26100.7623 for 11 24h2, 26200.7623 for 11 25h2, 20348.4648 for Server 2022, 25398.2092 for Server 2022 23h2, or 26100.32230 for Server 2025)
  2. Verify DWM process is running
    Open Task Manager, go to Details tab, and look for 'dwm.exe' or run 'tasklist | findstr dwm' from command prompt
    Affected if DWM process is running (this is the default state; the vulnerability affects any system where DWM is active)
  3. Check for installed security updates
    Run 'wmic qfe list' or check Windows Update history for recent security patches related to this DWM vulnerability
    Affected if No security update addressing this CVE is installed (the specific KB number varies by Windows version)

Your system is affected if it runs an unpatched Windows version within the affected build ranges AND has DWM enabled, which is the default state on most Windows systems.

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 available security patches for this vulnerability immediately. Restrict local administrative access and monitor for suspicious processes interacting with DWM. Consider disabling unnecessary DWM extensions or third-party visual themes until patch deployment.

Recommended fix High confidence

Upgrade to the specific fixed build number for your Windows version (e.g., Windows 10 22h2 to 10.0.19045.6809 or later; Windows 11 23h2 to 10.0.22631.6491 or later; Windows Server 2025 to 10.0.26100.32230 or later)

  1. 1. Identify the current Windows version by running `winver` or checking Settings > System > About
  2. 2. Determine which affected version category your system falls into from the list (Windows 10 21h2, 10 22h2, Windows 11 23h2/24h2/25h2, or Windows Server 2022/2022 23h2/2025)
  3. 3. Apply the appropriate Windows update that includes the security fix: for 21h2 use build 10.0.19044.6809+, for 22h2 use build 10.0.19045.6809+, for 11 23h2 use build 10.0.22631.6491+, for 11 24h2 use build 10.0.26100.7623+, for 11 25h2 use build 10.0.26200.7623+, for Server 2022 use build 10.0.20348.4648+, for Server 2022 23h2 use build 10.0.25398.2092+, for Server 2025 use build 10.0.26100.3223
  4. 4. Install all pending Windows Updates via Settings > Update & Security > Windows Update, or via WSUS/SCCM for enterprise deployments
  5. 5. Reboot the system to complete the update installation
  6. 6. Verify the vulnerability is remediated by confirming the build number matches or exceeds the fixed version for your Windows edition
Caveat Standard Windows update risks apply - ensure backups and test in staging if possible, but security patches generally have low breaking change risk

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

Fix this in Windows 10 21h2 Scoped from the published advisory
  • Consultation2.0 h
  • Implementation4.0 h
  • Testing3.0 h
  • Review / QA2.0 h
11.0 hours of engineering $1,930
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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-2026-20871 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