KB5126424: Cumulative update for .NET Framework, versions 3.5 and 4.8.1, on Windows 11 23H2, September 2026. Intermittent crashes in 64-bit .NET scenarios addressed

The update addresses two .NET Framework security vulnerabilities and intermittent crashes in some 64-bit scenarios. A restart is required if affected files are in use.

Does it affect you? Applies to: Devices running Windows 11, version 23H2, with .NET Framework 3.5 or 4.8.1 installed. Packages are available for x64 and Arm64.

What changes

Fixes 3 changes

.NET Framework

2 items

Addresses an elevation-of-privilege vulnerability in .NET Framework.¹
CVE-2026-62886.
Addresses a remote code execution vulnerability in .NET Framework.²
CVE-2026-69522.

NET Fundamentals

Intermittent crashes in some 64-bit .NET Framework scenarios are addressed.³

Technical details

Data sheet · Security · Downloads · Components Click to collapse or expand

Data sheet

Released: 2026-09-08
Classification: Security Updates
Type: Cumulative update
Restart: Required
Replaces: KB5120713, KB5101004, KB5087058, KB5082424

+4 earlier
KB5066133, KB5064403, KB5056580, KB5049624
Replaced by: KB5127692

Version	File version	Channel
3.5	2.0.50727.9183	General availability
4.8.1	4.8.9346.0	General availability

Security

2 vulnerabilities fixed

2 important

Vulnerability	Severity	CVSS
CVE-2026-69522 .NET and Visual Studio Remote Code Execution Vulnerability	Important	8.8
CVE-2026-62886 .NET Elevation of Privilege Vulnerability	Important	7.8

Downloads (Microsoft Update Catalog)

x64 Windows 11, version 23H2

76.2 MB

windows11.0-kb5126424-x64-ndp481.msu Main update · KB5126424 SHA-1: 3f28450a…d9dfe5

Arm64 Windows 11, version 23H2

93.1 MB

windows11.0-kb5126424-arm64-ndp481.msu Main update · KB5126424 SHA-1: a09da9df…dcb3a8

Updated components

42 files changed since the previous update for the same versions.

Top changed components	Files
WPF	22

Sources

Microsoft Support: KB5126424

Updated Oct 26, 2026

Cited passages from Microsoft's official notes (3)

1. This security update addresses an elevation of privilege vulnerability detailed in CVE-2026-62886. support.microsoft.com
2. This security update addresses a remote code execution vulnerability detailed in CVE-2026-69522. support.microsoft.com
3. Addresses an issue where intermittent crashes could occur in some 64-bit .NET Framework scenarios. support.microsoft.com

Checked automatically: 7 of 8 checks passed, 3 quoted passages · compared with Microsoft's page on Nov 8, 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: not passed

A second AI read the text against the sources: correctness 5/5, 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