Windows 10 21H2: security updates (KB) and vulnerabilities

2 KB updates fix 3 tracked CVEs for Windows 10 21H2.

Windows 10 21H2 has 3 tracked vulnerabilities, 0 critical. A fixed release or vendor patch exists for 3. Most recent: 2026-10-13. Highest priority: CVE-2026-96958 (score 52/100).

• CVE-2026-96958 HIGH 7.5 UPGRADE DOWNGRADE Inefficient algorithmic complexity in .NET allows an unauthorized attacker to deny service over a network.
• CVE-2026-108135 HIGH 7.0 UPGRADE UPGRADE Improper link resolution before file access ('link following') in Windows Backup Engine allows an authorized a
• CVE-2026-108396 HIGH 7.0 UPGRADE UPGRADE Time-of-check time-of-use (toctou) race condition in Windows Modern Device Management (MDM) allows an authoriz

FAQ

How do I fix Windows 10 21H2 vulnerabilities?

Open the CVE for your version, check the affected range, then follow the listed action: upgrade to the fixed release, or downgrade or mitigate if no fix exists yet. Commands for each OS are shown on every CVE page.

Is Windows 10 21H2 being exploited right now?

None of the tracked Windows 10 21H2 CVEs are on the CISA Known Exploited Vulnerabilities list at the moment. This is checked every 20 minutes.

Which Windows 10 21H2 CVE should I patch first?

CVE-2026-96958 currently ranks highest (52/100): Inefficient algorithmic complexity in .NET allows an unauthorized attacker to deny service over a network..

Security updates (KB) for Windows 10 21H2

Install the KB from Windows Update, then verify with Get-HotFix -Id KBxxxxxxx or winver. Fixed build is the OS build number after the update.

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