The Update BureauKB5122386: Cumulative update for .NET Framework, versions 3.5 and 4.8.1, on Windows 11 26H1, August 2026. Intermittent crashes in 64-bit .NET scenarios addressed
In short
Addresses an issue that could cause intermittent crashes in some 64-bit .NET Framework scenarios. A restart is required after installation if affected files are in use.
Does it affect you? Applies to: Devices running Windows 11, version 26H1, with .NET Framework 4.8.1 installed.
What changes
Fix 1 change
.NET Fundamentals
- An issue that could cause intermittent crashes in some 64-bit .NET Framework scenarios is addressed.1
Technical details
Data sheet · Security · Downloads · Components Click to collapse or expand
Data sheet
- Released
- 2026-08-27
- Classification
- Updates
- Type
- Cumulative update
- Restart
- Required
- Replaces
- KB5092431
- Replaced by
- KB5126053
| Version | File version | Channel |
|---|---|---|
| 3.5 | General availability | |
| 4.8.1 | 4.8.9345.0 | General availability |
Security
No vulnerabilities are listed for this update.
Downloads (Microsoft Update Catalog)
Arm64
Windows 11, version 26H1
57.2 MB
Updated components
25 files changed since the previous update for the same versions.
| Top changed components | Files |
|---|---|
| .NET runtime (CLR) | 12 |
Sources
Cited passages from Microsoft's official notes (1)
-
1.
Addresses an issue where intermittent crashes could occur in some 64-bit .NET Framework scenarios.
support.microsoft.com
Checked automatically: 8 of 8 checks passed, 1 quoted passage · compared with Microsoft's page on Oct 20, 2026
- Quotes found in the official pages: passed
- Numbers found in the sources: passed
- Vulnerabilities from the dossier only: passed
- Links to allowed domains only: passed
- Every official change covered: passed
- Readable plain text: passed
- Changes confirmed by the file list: passed
- Sources agree: passed
A second AI read the text against the sources: correctness 4/5, clarity 4/5, completeness 5/5. How we work
Published by The Update Bureau. Written with AI from Microsoft's own documents, checked by rules and a second AI. How we work · Report a mistake