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KB5120708: Overview with user sentiment and feedback

Last Updated September 30, 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 targets Windows 11 version 25H2 and Microsoft server operating system 24H2. The update addresses multiple critical vulnerabilities including remote code execution and elevation of privilege issues in the .NET Framework.

General Purpose

  • Addresses six security vulnerabilities including two remote code execution (RCE) flaws and two elevation of privilege vulnerabilities
  • Resolves CVE-2026-65810, CVE-2026-62872, CVE-2026-62886, CVE-2026-62897, CVE-2026-70354, and CVE-2026-62902
  • Implements security protections for font handling and XPS package boundary restrictions in WPF applications
  • Includes cumulative reliability improvements for .NET Framework components

General Sentiment

The update addresses significant security concerns with multiple critical vulnerabilities, making it an important security patch. However, the introduction of new security protections has created compatibility issues with certain WPF applications, particularly those handling fonts and XPS documents. Microsoft acknowledges these issues and provides workarounds, with resolution confirmed in the September 2026 update. The patch is recommended as part of regular maintenance routines, though users should be aware of potential application compatibility impacts.

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 but disables related security protections
  • WPF applications printing or displaying print preview from in-memory XPS documents registered with System.IO.Packaging.PackageStore may fail with System.IO.FileFormatException; workaround available but requires application rebuild or AppContext switch configuration

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 07:40 PM

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