The August 2026 .NET Framework updates introduce a regression that breaks printing and PDF export functionality in WPF applications by causing a System.IO.FileFormatException related to certain fonts. Affected platforms include Windows 10, Windows 11, and Windows Server versions from 2012 to 2025. Microsoft acknowledges the issue and recommends a temporary workaround involving an AppContext switch to disable font protection mechanisms, which may reduce security protections introduced by the update. The vendor is still investigating and has not yet released a permanent fix.

WPF applications that rely on printing or PDF/XPS export functionality may fail, disrupting normal operations for users and organizations dependent on these features. The temporary workaround disables security protections, potentially exposing systems to vulnerabilities addressed by the August 2026 update. There is no indication of active exploitation or credential compromise related to this issue.

Microsoft recommends applying the temporary workaround by enabling the Switch.MS.Internal.TtfDelta.DisableCmapAndSbitOverflowProtection AppContext switch in the application configuration only as a short-term measure. This workaround restores printing and PDF export functionality but disables protections against certain font-related vulnerabilities. Users should monitor for an official fix from Microsoft and apply it once available. Until then, use the workaround cautiously and only when necessary.