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KB5120709: Overview with user sentiment and feedback

Last Updated September 30, 2026

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Known Issues

Overview

Released on August 11, 2026, KB5120709 is a cumulative security and reliability update for .NET Framework 3.5 and 4.8.1 targeting Windows 10 Version 21H2 and 22H2. This patch addresses six critical security vulnerabilities including elevation of privilege and remote code execution issues. The update is recommended as part of regular maintenance routines to maintain system security and stability.

General Purpose

  • Addresses six CVEs including elevation of privilege vulnerabilities (CVE-2026-65810, CVE-2026-62872) and remote code execution flaws (CVE-2026-62886, CVE-2026-62897, CVE-2026-70354)
  • Resolves information disclosure vulnerability (CVE-2026-62902) in .NET Framework
  • Implements enhanced security protections for font handling and XPS package boundary restrictions
  • Cumulative reliability improvements for .NET Framework 3.5 and 4.8.1
  • Automatic deployment available through Windows Update and Microsoft Update

General Sentiment

This security-focused update addresses significant vulnerabilities and is recommended by Microsoft as part of standard maintenance. However, the patch introduces two known issues affecting WPF applications that print or generate PDF/XPS content. One issue is resolved in subsequent September 2026 updates, while the other remains under investigation. Users should be aware of potential compatibility concerns with certain font handling scenarios before deployment.

Known Issues

  • WPF applications may fail with System.IO.FileFormatException when printing or generating PDF/XPS content using certain fonts including Calibri; workaround available via AppContext switch (resolved in September 2026 update)
  • WPF applications printing from in-memory XPS documents registered with System.IO.Packaging.PackageStore may fail with System.IO.FileFormatException when using pack scheme package identities; workaround available via AppContext switch or code rebuild (status: investigating)

Disclaimer: We take measures to ensure that AI-generated content is of the highest possible quality, but we cannot guarantee its accuracy and recommend that users do their own independent research. Generated on 2026-09-30 01:50 PM

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