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

KB5082424

KB5082424: Cumulative update for .NET Framework, versions 3.5 and 4.8.1, on Windows 11 23H2, April 2026. Critical denial-of-service flaw addressed; ARM runtime crash improved

In short

The update addresses six .NET Framework vulnerabilities, including one critical denial-of-service flaw, and improves reliability for ClickOnce checks, ARM devices, and WCF services.

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.

File version
2.0.50727.9181 · 4.8.9332.0
Security
6 fixed · 1 critical
Restart
Required

What changes

Fixes 8 changes

.NET Framework

6 items
  • A flaw that could let an attacker run code remotely is addressed.1
    Addresses the remote code execution vulnerability CVE-2026-32178.
  • A flaw that could make a service unavailable is addressed.2
    Addresses the denial-of-service vulnerability CVE-2026-32203.
  • A flaw that could make a service unavailable is addressed.3
    Addresses the denial-of-service vulnerability CVE-2026-32226.
  • A flaw that could make a service unavailable is addressed.4
    Addresses the denial-of-service vulnerability CVE-2026-23666.
  • A flaw that could let someone bypass a security protection is addressed.5
    Addresses the security feature bypass vulnerability CVE-2026-26171.
  • A flaw that could expose information is addressed.6
    Addresses the information disclosure vulnerability CVE-2026-33116.

.NET Runtime

For: Devices with ARM64 processors

  • A crash in the .NET runtime is addressed for ARM64 devices when a program creates and catches a specific error within the same function.7
    Addresses an issue where the ARM64 CLR could crash when code generates and catches a NullReferenceException within the same function.

WCF

Verified in package

For: Devices running a WCF NamedPipe service in a Win32 app container

  • A problem that could stop a .NET communication service from running inside a Windows app container is addressed.8
    Addresses an issue with running a WCF NamedPipe service inside a Win32 app container on Windows 11 or Windows Server 2025.

Improvement 1 change

.NET Runtime

For: ClickOnce app users

  • Checks for ClickOnce apps can now use two additional methods to verify files.9
    Adds verification logic for ClickOnce to support SHA384 and SHA512.

Technical details

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

Data sheet

Released
2026-04-14
Classification
Security Updates
Type
Cumulative update
Restart
Required
Replaces
KB5066133, KB5064403, KB5056580, KB5049624
Replaced by
KB5087058
VersionFile versionChannel
3.5 2.0.50727.9181 General availability
4.8.1 4.8.9332.0 General availability

Security

6 vulnerabilities fixed
1 critical 2 important 3 not rated
VulnerabilitySeverityCVSS
CVE-2026-23666
.NET Framework Denial of Service Vulnerability
 Critical 7.5
CVE-2026-33116
.NET, .NET Framework, and Visual Studio Denial of Service Vulnerability
 Important 7.5
CVE-2026-32226
.NET Framework Denial of Service Vulnerability
 Important 5.9
CVE-2026-26171
.NET Denial of Service Vulnerability
 Not rated —
CVE-2026-32178
.NET Spoofing Vulnerability
 Not rated —
CVE-2026-32203
.NET and Visual Studio Denial of Service Vulnerability
 Not rated —

Updated components

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

Top changed componentsFiles
WCF14
.NET runtime (CLR)12
Windows Forms2

Verified in package: changed files confirm WCF.

Sources

Updated
Cited passages from Microsoft's official notes (9)
  1. 1. This security update addresses a remote code execution vulnerability detailed in CVE-2026-32178. support.microsoft.com
  2. 2. This security update addresses a denial-of-service vulnerability detailed in CVE-2026-32203. support.microsoft.com
  3. 3. This security update addresses a denial-of-service vulnerability detailed in CVE-2026-32226. support.microsoft.com
  4. 4. This security update addresses a denial-of-service vulnerability detailed in CVE-2026-23666. support.microsoft.com
  5. 5. This security update addresses a security feature bypass vulnerability detailed in CVE-2026-26171. support.microsoft.com
  6. 6. This security update addresses an information disclosure vulnerability detailed in CVE-2026-33116. support.microsoft.com
  7. 7. Addresses an issue where arm64 CLR could crash when code generates and catches a NullReferenceException within the same function support.microsoft.com
  8. 8. Addresses an issue with running a WCF NamedPipe service inside a Win32 app container when running on Windows 11 or Windows Server 2025. support.microsoft.com
  9. 9. Addresses an issue to add verification logic for ClickOnce to support SHA384 and SHA512 support.microsoft.com
Checked automatically: 7 of 8 checks passed, 9 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 4/5, 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