Microsoft has acknowledged a significant issue stemming from the .NET Framework updates released during the August 2026 Patch Tuesday, which are causing disruptions in printing and PDF export functionalities within certain applications.
Impact on WPF Applications
According to a Windows release health alert referenced by BleepingComputer, the problem specifically affects applications utilizing the Windows Presentation Foundation (WPF) UI framework. This open-source graphical subsystem is integral for developing Windows desktop client applications.
The company stated, “After installing the August 2026 .NET Framework cumulative update, some WPF applications may fail with a System.IO.FileFormatException when printing or generating PDF/XPS content that uses certain fonts, including Calibri.”
This issue extends across various platforms, encompassing both Windows client releases—such as the latest versions of Windows 10 and Windows 11—and Windows Server editions, ranging from Windows Server 2012 to Windows Server 2025.
Temporary Workaround Offered
While Microsoft is actively investigating the matter, it has provided a temporary workaround to assist users affected by these printing complications. This solution involves enabling the Switch.MS.Internal.TtfDelta.DisableCmapAndSbitOverflowProtection AppContext switch within the application configuration file. Users can implement this by adding the following code:
However, Microsoft has cautioned that employing this workaround will also disable certain protections introduced with the August 2026 .NET Framework update, potentially exposing the system to vulnerabilities that the recent security updates were designed to mitigate. The company advises that this workaround should only be utilized as a temporary measure and strictly when necessary to resolve the issue.
This situation echoes a similar incident from February 2021, when Microsoft addressed a known issue that led to crashes in WPF applications and Visual Studio following the installation of Windows 10 cumulative updates.
Additionally, on the same day, Microsoft shared a temporary workaround for another known issue triggered by Windows 11 updates released during the August 2026 Patch Tuesday, which caused games such as ARC Raiders, MARVEL Tōkon: Fighting Souls, and The Finals to crash and freeze.
