KB5087061 is a May 12, 2026 cumulative security update for .NET Framework 3.5 and 4.7.2 on Windows 10 Version 1809 and Windows Server 2019. This update addresses multiple security vulnerabilities and improves framework reliability for applications targeting these .NET Framework versions.
Knowledge BaseKB5087061Windows Update
KB5087061 — Cumulative Update for .NET Framework 3.5 and 4.7.2 for Windows 10 Version 1809
KB5087061 is a May 2026 cumulative update that addresses security vulnerabilities and reliability issues in .NET Framework 3.5 and 4.7.2 on Windows 10 Version 1809 and Windows Server 2019 systems.
13 May 2026 12 min read —
KB5087061Windows UpdateSecurity Update 5 fixes 12 min Windows 10 Version 1809 (Build 17763) +1Download
Quick Overview
PowerShell—Check if KB5087061 is installed
PS C:\> Get-HotFix -Id KB5087061# Returns patch details if KB5087061 is installed
Download Update
Download from Microsoft Update Catalog
Get the official update package directly from Microsoft
Diagnostic
Issue Description
Issue Description
This update addresses several security vulnerabilities and functional issues in .NET Framework 3.5 and 4.7.2 that could affect application stability and security on Windows 10 Version 1809 systems:
- Security vulnerabilities in .NET Framework runtime that could allow elevation of privilege
- Memory corruption issues in ASP.NET applications under high load conditions
- Incorrect handling of XML serialization in certain scenarios
- Performance degradation in WPF applications with complex data binding
- Potential denial of service vulnerabilities in .NET Framework networking components
Analysis
Root Causes
Root Cause
The issues stem from multiple components within .NET Framework 3.5 and 4.7.2, including improper input validation in the Common Language Runtime (CLR), insufficient bounds checking in ASP.NET request processing, and memory management inefficiencies in Windows Presentation Foundation (WPF) data binding operations.
Overview
KB5087061 is a cumulative security update released on May 12, 2026, targeting .NET Framework 3.5 and 4.7.2 on Windows 10 Version 1809 and Windows Server 2019 systems. This update addresses multiple security vulnerabilities and functional issues that could impact application stability and security.
Affected Systems
| Operating System | Version | Build | Architecture |
|---|---|---|---|
| Windows 10 | Version 1809 | 17763 | x64, x86 |
| Windows Server 2019 | Standard/Datacenter | 17763 | x64 |
Security Vulnerabilities Addressed
This update resolves several critical security issues:
- CVE-2026-0234: Elevation of privilege vulnerability in .NET Framework runtime
- CVE-2026-0235: Denial of service vulnerability in networking components
- Multiple memory corruption issues in ASP.NET request processing
- XML serialization security enhancements
Technical Improvements
Common Language Runtime (CLR) Enhancements
The update includes significant improvements to the CLR's memory management and security validation systems. Enhanced input validation prevents potential buffer overflow attacks, while improved garbage collection reduces memory fragmentation in long-running applications.
ASP.NET Framework Updates
ASP.NET applications benefit from improved thread safety and enhanced session state management. The update addresses race conditions that could lead to data corruption under high concurrent load scenarios, particularly affecting web applications with heavy traffic patterns.
Windows Presentation Foundation (WPF) Optimizations
WPF applications experience improved data binding performance through optimized change notification systems. Memory leak fixes in complex binding scenarios enhance application stability for data-intensive desktop applications.
Deployment Considerations
Enterprise Deployment
Organizations should test this update in non-production environments before widespread deployment. Pay particular attention to:
- Custom .NET Framework applications with complex object serialization
- High-traffic ASP.NET web applications
- WPF applications with extensive data binding
- Applications using reflection or dynamic code generation
Compatibility Testing
Recommended testing scenarios include:
- Load testing for ASP.NET applications
- XML serialization operations with complex object graphs
- WPF application performance under typical usage patterns
- Third-party component compatibility verification
Post-Installation Verification
After successful installation, verify the update using PowerShell:
Get-HotFix -Id KB5087061Check .NET Framework version information:
Get-ItemProperty "HKLM:SOFTWARE\Microsoft\NET Framework Setup\NDP\v4\Full\" -Name ReleaseRollback Information
If issues occur after installation, the update can be uninstalled through:
- Control Panel > Programs and Features > View installed updates
- PowerShell:
Remove-WindowsPackage -Online -PackageName - DISM command-line tool for server environments
Note: System restart is required after both installation and removal of this update.
Resolution Methods
Key Fixes & Changes
01
Fixes elevation of privilege vulnerability in .NET Framework runtime (CVE-2026-0234)
This update patches a critical security vulnerability in the Common Language Runtime that could allow an attacker to execute arbitrary code with elevated privileges. The fix implements proper input validation and bounds checking in CLR memory allocation routines. Applications using reflection or dynamic code generation benefit from enhanced security validation.
02
Resolves ASP.NET memory corruption under high concurrent load
Addresses memory corruption issues in ASP.NET applications when processing multiple concurrent requests. The update improves thread safety in request pipeline processing and fixes race conditions in session state management. Web applications experiencing intermittent crashes or data corruption under load will see improved stability.
03
Corrects XML serialization handling for complex object graphs
Fixes incorrect behavior in XML serialization when processing complex object hierarchies with circular references. The update enhances the XmlSerializer implementation to properly handle nested collections and custom type converters. Applications using XML serialization for data persistence or web service communication will experience more reliable serialization operations.
04
Improves WPF data binding performance and memory usage
Optimizes Windows Presentation Foundation data binding operations to reduce memory consumption and improve rendering performance. The update includes enhancements to the binding engine's change notification system and fixes memory leaks in complex binding scenarios. WPF applications with large data sets or frequent UI updates will see performance improvements.
05
Patches denial of service vulnerability in networking components (CVE-2026-0235)
Resolves a denial of service vulnerability in .NET Framework networking classes that could be exploited through malformed network requests. The fix implements proper request validation and resource management in HttpWebRequest and related networking components. Applications using .NET networking APIs are protected against potential DoS attacks.
Validation
Installation
Installation
This update is available through multiple distribution channels:
Windows Update
KB5087061 is automatically delivered via Windows Update to eligible systems. The update will be installed during the next scheduled update cycle or can be manually triggered through Settings > Update & Security > Windows Update.
Microsoft Update Catalog
Manual download is available from the Microsoft Update Catalog for enterprise environments requiring offline installation. The standalone package supports both x64 and x86 architectures for Windows 10 Version 1809.
Windows Server Update Services (WSUS)
Enterprise administrators can deploy this update through WSUS, System Center Configuration Manager (SCCM), or Microsoft Intune. The update is classified as a Security Update with High priority.
Prerequisites
- Windows 10 Version 1809
Build 17763or Windows Server 2019 - .NET Framework 3.5 and/or 4.7.2 must be installed
- Minimum 500 MB free disk space
- Administrative privileges required for installation
Installation Details
- File size: Approximately 45 MB for the complete package
- Restart required: Yes, system restart is required to complete installation
- Installation time: 5-10 minutes depending on system configuration
If it still fails
Known Issues
Known Issues
The following issues have been identified after installing KB5087061:
ASP.NET Application Pool Restart Required
Some ASP.NET applications may require manual application pool restart after installing this update to fully apply the fixes. Administrators should restart IIS application pools hosting .NET Framework applications to ensure proper functionality.
WPF Designer Issues in Visual Studio
Visual Studio WPF designers may experience temporary rendering issues immediately after the update installation. Restarting Visual Studio resolves this issue. This affects Visual Studio 2017 and 2019 when working with WPF projects targeting .NET Framework 4.7.2.
Third-Party Security Software Compatibility
Some third-party security software may flag the updated .NET Framework assemblies as suspicious during the first application launch after installation. This is a false positive and can be resolved by updating security software definitions or adding exceptions for .NET Framework directories.
Important: If installation fails with error code 0x80070643, ensure that Windows Installer service is running and that no other Windows updates are pending installation.
Frequently Asked Questions
What does KB5087061 resolve?+
KB5087061 resolves multiple security vulnerabilities in .NET Framework 3.5 and 4.7.2, including elevation of privilege (CVE-2026-0234) and denial of service (CVE-2026-0235) vulnerabilities, along with memory corruption issues in ASP.NET and performance improvements in WPF applications.
Which systems require KB5087061?+
This update applies to Windows 10 Version 1809 (Build 17763) and Windows Server 2019 systems that have .NET Framework 3.5 and/or 4.7.2 installed. Both x64 and x86 architectures are supported for Windows 10.
Is KB5087061 a security update?+
Yes, KB5087061 is classified as a security update with High priority. It addresses critical security vulnerabilities including CVE-2026-0234 and CVE-2026-0235, along with other security enhancements in .NET Framework components.
What are the prerequisites for KB5087061?+
Prerequisites include Windows 10 Version 1809 or Windows Server 2019, .NET Framework 3.5 and/or 4.7.2 installed, minimum 500 MB free disk space, and administrative privileges. A system restart is required after installation.
Are there known issues with KB5087061?+
Known issues include the need to restart ASP.NET application pools manually, temporary WPF designer rendering issues in Visual Studio, and potential false positives from third-party security software. Installation may fail with error 0x80070643 if Windows Installer service is not running.
References (3)
1
KB5087061 : Mise à jour cumulative pour .NET Framework 3.5 et 4.7.2Article de support officiel de Microsoft pour KB5087061 avec des informations complètes sur l'installation et le dépannagehttps://support.microsoft.com/en-us/topic/may-12-2026-kb5087061-cumulative-update-for-net-framework-3-5-and-4-7-2-for-windows-10-version-1809-and-windows-server-2019-177bd820-c188-4b3b-8d38-d99c8daa809e
2Mises à jour de sécurité du .NET FrameworkDocumentation Microsoft Learn sur les versions de .NET Framework et les dépendances des mises à jour de sécuritéhttps://learn.microsoft.com/en-us/dotnet/framework/migration-guide/versions-and-dependencies
3Guide de déploiement de Windows UpdateConseils de déploiement d'entreprise pour les mises à jour Windows, y compris les mises à jour du .NET Frameworkhttps://learn.microsoft.com/en-us/windows/deployment/update/
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