Microsoft August Updates Cause Printing and PDF Export Issues in WPF Apps

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Microsoft acknowledges issues with August 2026 .NET Framework updates causing printing and PDF generation problems in WPF applications.

Microsoft’s Acknowledgment

Microsoft has confirmed that updates released during the August 2026 Patch Tuesday for the .NET Framework are causing issues with printing and PDF generation in certain applications. A Windows release health alert disclosed by BleepingComputer confirms that the problem affects software utilizing the Windows Presentation Foundation (WPF) graphical framework, which is used for developing desktop client applications on Windows.

Impact and Affected Systems

Technical Details of the Issue

The issue arises after installing the August 2026 .NET Framework cumulative update, leading to a System.IO.FileFormatException in some WPF applications when printing or generating PDF/XPS content that incorporates specific fonts, such as Calibri. This disruption impacts both Windows client operating systems, including the latest versions of Windows 10 and Windows 11, as well as Windows Server editions ranging from Windows Server 2012 to Windows Server 2025.

Workaround Provided

Microsoft is investigating the root cause and has provided a temporary workaround to mitigate the problem. Users are advised to modify the application configuration file by enabling the Switch.MS.Internal.TtfDelta.DisableCmapAndSbitOverflowProtection AppContext switch with the following code:

However, the company cautions that this adjustment disables security protections introduced in the August 2026 update, potentially leaving systems vulnerable to exploits addressed by the patch. Microsoft emphasizes that this solution should only be used temporarily and strictly when necessary to resolve the issue.

Past WPF-Related Disruptions

This is not the first instance of WPF-related disruptions. In February 2021, Microsoft resolved a similar problem that caused WPF applications and Visual Studio to crash following Windows 10 cumulative updates. Additionally, Microsoft recently issued a separate workaround for gaming applications affected by August 2026 Windows 11 updates, including titles like ARC Raiders, MARVEL T kon: Fighting Souls, and The Finals, which experienced crashes and freezes.

Security Analysis Insights

A separate analysis, the Blue Report 2026, evaluated security measures across 338 million simulated attacks in production environments. The findings indicate that 37% of malicious activities are blocked after threat actors obtain valid credentials, highlighting gaps in endpoint defenses.

The issue underscores the challenges of balancing security updates with compatibility in complex software ecosystems. Organizations using WPF-based applications are urged to monitor Microsoft’s official channels for a permanent resolution while applying the recommended workaround with caution.