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.NET Framework 3.5 / 4.8.1 .NET Framework 3.5 / 4.8.1 Security update
Patch Tuesday

KB5074837

KB5074837: Cumulative update for .NET Framework, versions 3.5 and 4.8.1, on Windows 11 26H1, February 2026. .NET information disclosure flaw and runtime issues addressed

In short

The update addresses CVE-2025-55248, an information disclosure vulnerability, and three .NET Runtime reliability issues, including a possible crash on Arm64.

Does it affect you? Applies to: Devices running Windows 11, version 26H1, on Arm64 with .NET Framework 4.8.1 installed.

File version
4.8.9325.0
Security
1 fixed
Restart
Required

What changes

Fixes 3 changes

.NET Framework

  • Addresses an information disclosure vulnerability in .NET Framework.1
    Addresses CVE-2025-55248.

.NET Runtime

2 items
  • Updates operating system calls to comply with current standards.2
  • Addresses a possible crash on Arm64 when code generates and catches a NullReferenceException within the same function.3
    The affected component is the Arm64 CLR.

Improvement 1 change

.NET Runtime

  • ClickOnce verification supports SHA384 and SHA512.4

Technical details

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

Data sheet

Released
2026-02-10
Classification
Security Updates
Type
Cumulative update
Restart
Required
Replaced by
KB5082421
VersionFile versionChannel
3.5 General availability
4.8.1 4.8.9325.0 General availability

Security

1 vulnerability fixed
1 not rated
VulnerabilitySeverityCVSS
CVE-2025-55248
.NET, .NET Framework, and Visual Studio Information Disclosure Vulnerability
 Not rated —

Downloads (Microsoft Update Catalog)

Arm64 Windows 11, version 26H1
54.9 MB
windows11.0-kb5074837-arm64-ndp481.msu Main update · KB5074837 SHA-1: c760ba3c…3c06bf

Sources

Updated
Cited passages from Microsoft's official notes (4)
  1. 1. This security update addresses an information disclosure vulnerability detailed in CVE-2025-55248. support.microsoft.com
  2. 2. Addresses an issue to update operating system calls for compliance with current standards. support.microsoft.com
  3. 3. Addresses an issue in cases where the arm64 CLR could crash when code generates and catches a NullReferenceException within the same function. support.microsoft.com
  4. 4. Addresses an issue to add verification logic for ClickOnce to support SHA384 and SHA512. support.microsoft.com
Checked automatically: 7 of 8 checks passed, 4 quoted passages · compared with Microsoft's page on Sep 25, 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