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

KB5066131

KB5066131: Cumulative update for .NET Framework, versions 3.5 and 4.8.1, on Windows 11 24H2 and Windows Server 2025, October 2025. Information disclosure flaw in the managed runtime addressed

In short

The update addresses one Important-severity information disclosure vulnerability in .NET Framework: CVE-2025-55248.

Does it affect you? Applies to: Devices running Windows 11, version 24H2, or Windows Server 2025 with .NET Framework 3.5 or 4.8.1 installed.

File version
2.0.50727.9180 · 4.8.9320.0
Security
1 fixed
Restart
Required

What changes

Fix 1 change

.NET Framework

  • An information disclosure vulnerability is addressed.1
    Addresses CVE-2025-55248.

Technical details

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

Data sheet

Released
2025-10-14
Classification
Security Updates
Type
Cumulative update
Restart
Required
Replaces
KB5064401, KB5056579, KB5054979, KB5050577
+4 earlier KB5049622, KB5048162, KB5045934, KB5044030
Replaced by
KB5082417
VersionFile versionChannel
3.5 2.0.50727.9180 General availability
4.8.1 4.8.9320.0 General availability

Security

1 vulnerability fixed
1 important
VulnerabilitySeverityCVSS
CVE-2025-55248
.NET, .NET Framework, and Visual Studio Information Disclosure Vulnerability
 Important 4.8

Downloads (Microsoft Update Catalog)

x64 Windows 11, version 24H2 / Windows Server 2025
71.6 MB
windows11.0-kb5066131-x64-ndp481.msu Main update · KB5066131 SHA-1: b2ab1290…66f615
Arm64 Windows 11, version 24H2 / Windows Server 2025
88.2 MB
windows11.0-kb5066131-arm64-ndp481.msu Main update · KB5066131 SHA-1: 3beead80…7e1c13

Updated components

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

Top changed componentsFiles
WPF24
.NET runtime (CLR)12
ASP.NET10
Windows Forms2

Sources

Updated
Cited passages from Microsoft's official notes (1)
  1. 1. This security update addresses an information disclosure vulnerability detailed in CVE-2025-55248. support.microsoft.com
Checked automatically: 7 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: 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