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

KB5066128

KB5066128: Cumulative update for .NET Framework, versions 3.5 and 4.8.1, on Windows 11 25H2, October 2025. Information exposure flaw fixed in .NET

In short

Fixes a flaw that could expose information in .NET Framework. It applies to Windows 11 version 25H2 with .NET Framework 3.5 or 4.8.1 installed.

Does it affect you? Applies to: Devices running Windows 11, version 25H2, with .NET Framework 3.5 or 4.8.1 installed.

File version
2.0.50727.9180 · 4.8.9321.0
Security
1 fixed
Restart
Required

What changes

Fix 1 change

.NET Framework

  • A flaw that could expose information is fixed.1
    Addresses CVE-2025-55248, an information disclosure vulnerability in .NET Framework.

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
KB5066613
Replaced by
KB5082417
VersionFile versionChannel
3.5 2.0.50727.9180 General availability
4.8.1 4.8.9321.0 General availability

Security

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

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 5/5, 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