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Recorded 21 Oct 2026 at 10:34 UTC. This is what ChangeIntel recorded, including the title, summary, facts and links. It is not a statement of the source's current position. See the latest record.

.NET Framework updateMicrosoft Learn and Support

KB5126421

September 8, 2026-KB5126421 Cumulative Update for .NET Framework 3.5 and 4.8.1 for Windows 10 Version 21H2 and Windows 10 Version 22H2

What it said

KB
KB5126421
Applies to
Windows 10, version 21H2; Windows 10, version 22H2
Related KBs
KB5126145, KB5126146
CVEs named by Microsoft
Readiness
This is a .NET Framework servicing update, not a Windows OS build. Review Microsoft's support article and test the applicable framework versions; OS release-health coverage does not establish this update's deployment readiness.
Windows versions and builds
Not in the collected release tables
Restart required
Not stated in collected security fixes
CVEs fixed
CVE-2026-69522, CVE-2026-62886
Known issues caused
None in the collected release health data
Known issues resolved
None in the collected release health data
Included security update
None identified in the collected release tables
CVEs listed directly for this KB
CVE-2026-69522, CVE-2026-62886
Missing security release
None identified in collected security coverage

Source evidence when recorded

dotnet-framework-updates
IncompleteRead 21 Oct 2026 at 03:59 UTC
Microsoft security releases
Complete at observationRead 21 Oct 2026 at 10:33 UTC

Coverage describes the sources at this observation. A complete read then does not establish their current position.

What changed

  1. Security fixes updated · Applies to: Microsoft .NET Framework 3.5 AND 4.8.1 on Windows 10 Version 21H2 for 32-bit Systems, Microsoft .NET Framework 3.5 AND 4.8.1 on Windows 10 Version 21H2 for ARM64-based Systems, Microsoft .NET Framework 3.5 AND 4.8.1 on Windows 10 Version 21H2 for x64-based Systems, Microsoft .NET Framework 3.5 AND 4.8.1 on Windows 10 Version 22H2 for 32-bit Systems, Microsoft .NET Framework 3.5 AND 4.8.1 on Windows 10 Version 22H2 for ARM64-based Systems, Microsoft .NET Framework 3.5 AND 4.8.1 on Windows 10 Version 22H2 for x64-based Systems → Windows 10, version 21H2; Windows 10, version 22H2
  2. Applies to: Microsoft .NET Framework 3.5 AND 4.8.1 on Windows 10 Version 21H2 for 32-bit Systems, Microsoft .NET Framework 3.5 AND 4.8.1 on Windows 10 Version 21H2 for ARM64-based Systems, Microsoft .NET Framework 3.5 AND 4.8.1 on Windows 10 Version 21H2 for x64-based Systems, Microsoft .NET Framework 3.5 AND 4.8.1 on Windows 10 Version 22H2 for 32-bit Systems, Microsoft .NET Framework 3.5 AND 4.8.1 on Windows 10 Version 22H2 for ARM64-based Systems, Microsoft .NET Framework 3.5 AND 4.8.1 on Windows 10 Version 22H2 for x64-based Systems, Microsoft .NET Framework 3.5 AND 4.8 on Windows 10 Version 1809 for 32-bit Systems, Microsoft .NET Framework 3.5 AND 4.8 on Windows 10 Version 1809 for ARM64-based Systems, Microsoft .NET Framework 3.5 AND 4.8 on Windows 10 Version 1809 for x64-based Systems → Microsoft .NET Framework 3.5 AND 4.8.1 on Windows 10 Version 21H2 for 32-bit Systems, Microsoft .NET Framework 3.5 AND 4.8.1 on Windows 10 Version 21H2 for ARM64-based Systems, Microsoft .NET Framework 3.5 AND 4.8.1 on Windows 10 Version 21H2 for x64-based Systems, Microsoft .NET Framework 3.5 AND 4.8.1 on Windows 10 Version 22H2 for 32-bit Systems, Microsoft .NET Framework 3.5 AND 4.8.1 on Windows 10 Version 22H2 for ARM64-based Systems, Microsoft .NET Framework 3.5 AND 4.8.1 on Windows 10 Version 22H2 for x64-based Systems
Page history

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Cite this version
Field-level log (17)

Up to 100 recent field edits are shown; older edits may be outside retention.

  1. 21 Oct 2026 · 10:34:24 UTC Source coverage: dotnet-framework-updatesCurrent → Incomplete
  2. 21 Oct 2026 · 04:01:31 UTC Source coverage: dotnet-framework-updatesIncomplete → Current
  3. 19 Oct 2026 · 15:12:40 UTC ReadinessThis is a .NET Framework servicing update, not a Windows OS build. Review Microsoft's support article and test the applicable framework versions; OS release-health coverage does not establish this update's deployment readiness.
  4. 19 Oct 2026 · 15:12:40 UTC CVEs named by Microsoft
  5. 19 Oct 2026 · 15:12:40 UTC Related KBsKB5126145, KB5126146
  6. 19 Oct 2026 · 15:12:40 UTC Applies toMicrosoft .NET Framework 3.5 AND 4.8.1 on Windows 10 Version 21H2 for 32-bit Systems, Microsoft .NET Framework 3.5 AND 4.8.1 on Windows 10 Version 21H2 for ARM64-based Systems, Microsoft .NET Framework 3.5 AND 4.8.1 on Windows 10 Version 21H2 for x64-based Systems, Microsoft .NET Framework 3.5 AND 4.8.1 on Windows 10 Version 22H2 for 32-bit Systems, Microsoft .NET Framework 3.5 AND 4.8.1 on Windows 10 Version 22H2 for ARM64-based Systems, Microsoft .NET Framework 3.5 AND 4.8.1 on Windows 10 Version 22H2 for x64-based Systems → Windows 10, version 21H2; Windows 10, version 22H2
  7. 19 Oct 2026 · 15:12:40 UTC Source coverage: windows-known-issuesCurrent → Not collected
  8. 19 Oct 2026 · 15:12:40 UTC Source coverage: dotnet-framework-updatesIncomplete
  9. 19 Oct 2026 · 15:12:40 UTC Link: KB5126146/windows/kb/KB5126146
  10. 19 Oct 2026 · 15:12:40 UTC Link: KB5126145/windows/kb/KB5126145
  11. 19 Oct 2026 · 15:12:40 UTC Link: Support articlehttps://support.microsoft.com/help/5126421 → https://support.microsoft.com/en-us/servicing/dotnetframework/2026/09/september-8-2026-kb5126421-cumulative-update-for-net-framework-3-5-and-4-8-1-for-windows-10-version
  12. 19 Oct 2026 · 15:12:40 UTC SourceMicrosoft release information, MSRC and Windows release health → Microsoft Learn and Support
  13. 19 Oct 2026 · 15:12:40 UTC KindWindows update → .NET Framework update
  14. 19 Oct 2026 · 15:12:40 UTC SummarySecurity update fixing 2 collected CVEs. → September 8, 2026-KB5126421 Cumulative Update for .NET Framework 3.5 and 4.8.1 for Windows 10 Version 21H2 and Windows 10 Version 22H2
  15. 16 Oct 2026 · 15:49:54 UTC Applies toMicrosoft .NET Framework 3.5 AND 4.8.1 on Windows 10 Version 21H2 for 32-bit Systems, Microsoft .NET Framework 3.5 AND 4.8.1 on Windows 10 Version 21H2 for ARM64-based Systems, Microsoft .NET Framework 3.5 AND 4.8.1 on Windows 10 Version 21H2 for x64-based Systems, Microsoft .NET Framework 3.5 AND 4.8.1 on Windows 10 Version 22H2 for 32-bit Systems, Microsoft .NET Framework 3.5 AND 4.8.1 on Windows 10 Version 22H2 for ARM64-based Systems, Microsoft .NET Framework 3.5 AND 4.8.1 on Windows 10 Version 22H2 for x64-based Systems, Microsoft .NET Framework 3.5 AND 4.8 on Windows 10 Version 1809 for 32-bit Systems, Microsoft .NET Framework 3.5 AND 4.8 on Windows 10 Version 1809 for ARM64-based Systems, Microsoft .NET Framework 3.5 AND 4.8 on Windows 10 Version 1809 for x64-based Systems → Microsoft .NET Framework 3.5 AND 4.8.1 on Windows 10 Version 21H2 for 32-bit Systems, Microsoft .NET Framework 3.5 AND 4.8.1 on Windows 10 Version 21H2 for ARM64-based Systems, Microsoft .NET Framework 3.5 AND 4.8.1 on Windows 10 Version 21H2 for x64-based Systems, Microsoft .NET Framework 3.5 AND 4.8.1 on Windows 10 Version 22H2 for 32-bit Systems, Microsoft .NET Framework 3.5 AND 4.8.1 on Windows 10 Version 22H2 for ARM64-based Systems, Microsoft .NET Framework 3.5 AND 4.8.1 on Windows 10 Version 22H2 for x64-based Systems
  16. 14 Oct 2026 · 11:22:42 UTC Missing security releaseUnknown: security evidence is incomplete or retained → None identified in collected security coverage
  17. 14 Oct 2026 · 11:22:42 UTC Source coverage: msrc-cvrfIncomplete → Current
ChangeIntel

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Sources read 11 Nov 20:03 UTC · 274 of 275 readable · 273 fully read · documentation 469/469 current

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