Microsoft's August 2026 .NET Framework cumulative update for Windows 11 causes WPF applications to fail when printing or generating PDF or XPS content that uses the Calibri font or related fonts such as Cambria, Constantia, or Corbel, according to Bleeping Computer. The error is reported as a System.IO.FileFormatException, and users who switch to fonts such as Arial, Times New Roman, Verdana, Tahoma, Segoe UI, or Calibri Light do not experience the issue. The update, released in August 2026, also introduces stability problems for some games that run alongside RGB peripherals, causing crashes or freezes. Microsoft provided a temporary workaround that disables a security protection introduced in the update by adding the setting value="Switch.MS.Internal.TtfDelta.DisableCmapAndSbitOverflowProtection=true" to an application's configuration file, or by changing the font used in the documents. Microsoft said it is working to resolve the printing bug and will release a fix in a subsequent update. In the meantime, users seeking to maintain system security are advised to use alternative fonts or apply the configuration change, which removes the protection that the update added.