Microsoft has acknowledged that updates to the .NET Framework issued during the August 2026 Patch Tuesday are causing issues with printing and PDF export in certain applications.
According to a Windows release health alert reported by BleepingComputer, this known problem specifically impacts applications utilizing the Windows Presentation Foundation (WPF) UI framework, which is an open-source graphical subsystem designed for creating Windows desktop client applications.
Microsoft states, “Following the installation of the August 2026 .NET Framework cumulative update, some WPF applications may encounter a System.IO.FileFormatException when attempting to print or generate PDF/XPS content that incorporates specific fonts, such as Calibri.”
The full list of affected platforms includes both Windows client versions (including the most recent iterations of Windows 10 and Windows 11) as well as Windows Server (ranging from Windows Server 2012 to Windows Server 2025).
Microsoft is currently investigating the matter and, until a permanent fix can be provided, has offered a temporary workaround to assist users facing these printing issues.
This workaround involves enabling the Switch.MS.Internal.TtfDelta.DisableCmapAndSbitOverflowProtection AppContext switch in the application configuration file by adding the following:
<configuration>
<runtime>
<AppContextSwitchOverrides
value=”Switch.MS.Internal.TtfDelta.DisableCmapAndSbitOverflowProtection=true”/>
</runtime>
</configuration>
However, the company cautioned that implementing this workaround will also disable the protections introduced with the August 2026 .NET Framework update, potentially leaving the system vulnerable to attacks that could exploit the vulnerabilities addressed in this month’s security updates.
“Microsoft advises using this workaround solely as a temporary solution and only when necessary to resolve this issue,” it cautioned.
Approximately five years ago, in February 2021, Microsoft resolved another known issue that led to crashes in WPF applications and Visual Studio following the installation of Windows 10 cumulative updates.
On Friday, Microsoft also provided a temporary workaround for a known issue caused by Windows 11 updates released during the August 2026 Patch Tuesday, which resulted in games such as ARC Raiders, MARVEL Tōkon: Fighting Souls, and The Finals crashing and freezing.
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Source: Original article
