KB5120709: Overview with user sentiment and feedback

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 multiple remote code execution and elevation of privilege issues. Microsoft recommends applying this update as part of regular maintenance routines.

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)
• Provides cumulative reliability improvements to .NET Framework components
• Applicable to both Windows 10 21H2 and 22H2 versions
• Available through Windows Update, Microsoft Update, and WSUS channels

General Sentiment

This patch addresses significant security concerns with multiple critical vulnerabilities, making it an important security release. However, the update introduces two documented issues affecting WPF applications that handle printing and PDF/XPS content generation. Microsoft has provided workarounds for both issues, though they involve disabling security protections as temporary measures. The first issue is confirmed resolved in the September 2026 update, while the second remains under investigation.

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; status under investigation

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 2026-09-22 07:52 AM

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