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KB5120708: Overview with user sentiment and feedback

Last Updated September 25, 2026

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Known Issues

Overview

KB5120708 is a cumulative security and reliability update for .NET Framework 3.5 and 4.8.1 released on August 11, 2026. It applies to Windows 11 version 25H2 and Microsoft server operating system 24H2. This update addresses six critical security vulnerabilities including elevation of privilege and remote code execution issues affecting the .NET Framework runtime.

General Purpose

  • Addresses six security vulnerabilities: two elevation of privilege flaws (CVE-2026-65810, CVE-2026-62872), three remote code execution vulnerabilities (CVE-2026-62886, CVE-2026-62897, CVE-2026-70354), and one information disclosure issue (CVE-2026-62902)
  • Implements enhanced font and XPS package boundary protections in WPF applications
  • Recommended as part of regular maintenance routines for affected Windows and server systems
  • Available through Windows Update, Microsoft Update, and WSUS channels

General Sentiment

This update carries significant security importance due to the critical vulnerabilities it resolves. However, the introduction of new WPF application compatibility issues has generated concern in the community. The known issues involve font rendering failures and XPS document processing errors that can break existing applications. Microsoft has acknowledged these problems and released a subsequent September 2026 update that resolves the primary font-related issue, indicating they took community feedback seriously.

Known Issues

  • WPF applications may fail with System.IO.FileFormatException when printing or generating PDF/XPS content using certain fonts including Calibri (resolved in September 2026 update)
  • WPF applications printing or displaying print preview from in-memory XPS documents registered with System.IO.Packaging.PackageStore may fail with System.IO.FileFormatException when using pack scheme URIs (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 2026-09-25 07:49 PM

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