KB5121645: Overview with user sentiment and feedback

Overview

KB5121645 is a cumulative security and quality update for .NET Framework 3.5, 4.7.2, and 4.8 released on August 11, 2026. This patch addresses multiple critical vulnerabilities affecting Windows 10 version 1809 and Windows Server 2019. The update includes six security fixes covering elevation of privilege, remote code execution, and information disclosure vulnerabilities in the .NET Framework.

General Purpose

• Addresses CVE-2026-65810 and CVE-2026-62872 elevation of privilege vulnerabilities in .NET Framework
• Patches three remote code execution vulnerabilities (CVE-2026-62886, CVE-2026-62897, CVE-2026-70354)
• Resolves CVE-2026-62902 information disclosure vulnerability
• Delivers cumulative quality and reliability improvements for supported .NET Framework versions

General Sentiment

The patch addresses significant security concerns with multiple critical vulnerabilities, which is positive for system security posture. However, a confirmed known issue exists affecting WPF applications that use certain fonts when printing or generating PDF/XPS content. Microsoft is actively investigating this issue and provides a workaround, though the workaround requires disabling some security protections introduced in this update, creating a trade-off between functionality and security.

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 (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 2026-09-02 07:18 AM

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