Home/KB Catalog/KB5121649

KB5121649: Overview with user sentiment and feedback

Last Updated September 5, 2026

Probability of successful installation and continued operation of the machine

0%
20%
40%
60%
80%
100%
60%
Known Issues

Overview

KB5121649 is a Security and Quality Rollup released on August 11, 2026, for .NET Framework versions 3.5, 4.6.2, 4.7, 4.7.1, 4.7.2, and 4.8 on Windows Server 2012 R2. This cumulative update addresses multiple critical security vulnerabilities including elevation of privilege and remote code execution issues. The patch is available through Windows Update, Microsoft Update Catalog, and Windows Server Update Services (WSUS).

General Purpose

  • Addresses six critical security vulnerabilities including CVE-2026-65810 and CVE-2026-62872 (elevation of privilege)
  • Resolves three remote code execution vulnerabilities (CVE-2026-62886, CVE-2026-62897, CVE-2026-70354)
  • Patches information disclosure vulnerability CVE-2026-62902
  • Includes quality and reliability improvements across supported .NET Framework versions
  • Applies to multiple .NET Framework versions with consolidated rollup delivery

General Sentiment

This is a critical security patch addressing serious vulnerabilities in .NET Framework components. While the security fixes are essential for system protection, the update introduces known compatibility issues with WPF applications, particularly affecting printing and PDF/XPS generation functionality. Microsoft has provided workarounds for affected applications, though these require temporary disabling of security protections. Organizations should prioritize deployment for security reasons but should test thoroughly in their environment first.

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 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 when using pack scheme URIs; rebuild with alternative URI scheme or use AppContext switch workaround

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 2026-09-05 01:14 AM

Back to Knowledge Base Catalog