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

KB5126422

KB5126422: Cumulative update for .NET Framework, versions 3.5 and 4.8.1, on Windows Server 2022, September 2026. Remote code execution and privilege-escalation flaws addressed

In short

The update addresses two .NET vulnerabilities, including a remote code execution flaw. Microsoft later removed CVE-2026-62886 from the KB page’s vulnerability listing.

Does it affect you? Applies to: Devices running Windows Server 2022 with .NET Framework 3.5 or 4.8.1 installed.

File version
2.0.50727.9183 · 4.8.9346.0
Security
2 fixed
Restart
Required
Review notes Additional details from the official release notes (2) Read notes
  • In short The supplied KB page says this update addresses CVE-2026-62886, an elevation-of-privilege vulnerability.
  • In detail The supplied KB page says this update addresses CVE-2026-62886, an elevation-of-privilege vulnerability.

The official sources are linked at the end of the page.

What changes

Fixes 2 changes

.NET Framework

2 items

For: devices with .NET Framework 3.5 or 4.8.1

  • Addresses a vulnerability that could let an attacker gain elevated privileges.1
    Addresses CVE-2026-62886, an elevation of privilege vulnerability.
  • Addresses a vulnerability that could let an attacker run code remotely.2
    Addresses CVE-2026-69522, a remote code execution vulnerability.

Improvement 1 change

.NET Framework

For: devices with .NET Framework 3.5 or 4.8.1

  • Includes cumulative reliability improvements for .NET Framework 3.5 and 4.8.1.3

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
KB5120714, KB5101005
Replaced by
KB5127693
VersionFile versionChannel
3.5 2.0.50727.9183 General availability
4.8.1 4.8.9346.0 General availability

Security

2 vulnerabilities fixed
1 important 1 not rated
VulnerabilitySeverityCVSS
CVE-2026-69522
.NET and Visual Studio Remote Code Execution Vulnerability
 Important 8.8
CVE-2026-62886
.NET Elevation of Privilege Vulnerability
 Not rated —

Downloads (Microsoft Update Catalog)

x64 Windows Server 2022
76.2 MB
windows10.0-kb5126422-x64-ndp481.msu Main update · KB5126422 SHA-1: 1e92b256…1d8168

Updated components

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

Top changed componentsFiles
WPF22

Sources

Updated
Cited passages from Microsoft's official notes (3)
  1. 1. This security update addresses an elevation of privilege vulnerability detailed in CVE-2026-62886. support.microsoft.com
  2. 2. This security update addresses a remote code execution vulnerability detailed in CVE-2026-69522. support.microsoft.com
  3. 3. The September 8, 2026 update for Windows Server 2022 includes security and cumulative reliability improvements in .NET Framework 3.5 and 4.8.1. 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 3/5, 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