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CISA KEV · ACTIVELY EXPLOITED
HIGH severity

CVE-2026-21519 — Windows 10 21h2

HIGH

CVE-2026-21519 is a high-severity (CVSS 7.8) CWE-843 vulnerability in microsoft windows 10 21h2. It is in CISA's Known Exploited Vulnerabilities catalog (added 2026-02-10) — treat it as actively exploited and patch now. A fix is available — see the affected versions and patch details below.

Access of resource using incompatible type ('type confusion') in Desktop Window Manager allows an authorized attacker to elevate privileges locally.

Published
Updated
Affected
12 products
Patched
See advisory
Exploits
None indexed
Exploitation data as of Oct 23, 2026 · OSV.dev, NVD, CISA KEV, FIRST.org (EPSS)

Exploitation Status

Actively exploited in the wild

  • Confirmed by CISA's Known Exploited Vulnerabilities catalog on 2026-02-10. Federal agencies were required to remediate by 2026-03-03.
  • A successful exploit gives an attacker total control of the affected component, not partial access.

Exploitation and automatability from CISA (KEV catalog and SSVC triage) for CVE-2026-21519.

EPSS Exploitation Probability

via FIRST.org ↗
2.5%probability of exploitation in next 30 days
Lower Risk+0.02%
Lower risk than most CVEs84th percentile — riskier than 84% of all scored CVEsHighest risk
1.79%2.91%4.03%5.15%4.5%2.5%May 26Sep 26Oct 26

Probability of exploitation in the next 30 days, from FIRST.org EPSS.

How urgent is this, really

CVE-2026-21519 by exploitation likelihood (EPSS) against impact (CVSS). Outside the shaded patch-first corner.

Where this sits among everything scored

Of 394,803 CVEs with a current EPSS score, this one falls in the < 10% band (highlighted). Counts from FIRST.org, log-scaled.

Description

Access of resource using incompatible type ('type confusion') in Desktop Window Manager allows an authorized attacker to elevate privileges locally.

Affected Products

12 products · 21 configurations
OS
windows 10 21h2microsoft
< 10.0.19044.6937
range
OS
windows 10 22h2microsoft
< 10.0.19045.6937
range
OS
windows 10 1607microsoft
< 10.0.14393.8868
range
OS
windows 10 1809microsoft
< 10.0.17763.8389
range
OS
windows 11 23h2microsoft
< 10.0.22631.6649
range
OS
windows 11 24h2microsoft
< 10.0.26100.7781
range

Detection & mitigation playbook

Vendor / appliance

  1. Detect

    Inventory every microsoft windows 10 21h2 deployment and check each version against the affected-products list above.

  2. Fix

    Apply the microsoft windows 10 21h2 security patch or hotfix for CVE-2026-21519 on the affected version, following the vendor advisory for your exact build.

  3. Workarounds

    If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands. Alongside that, restrict the management interface to trusted networks and apply the vendor's recommended configuration mitigations.

Frequently Asked Questions

Access of resource using incompatible type ('type confusion') in Desktop Window Manager allows an authorized attacker to elevate privileges locally.
O3 Security · Runtime Protection

Is CVE-2026-21519 being exploited in your environment?

Detect and block the exploit chain at execution, on systems you cannot patch yet.

Protect my workloads How runtime protection works
CVE-2026-21519: Windows 10 21h2 (High 7.8, KEV)