Microsoft has confirmed a new Windows 11 issue affecting some Windows Presentation Foundation applications after installation of the August 2026 .NET Framework cumulative update.
The problem can prevent WPF applications from printing documents or generating PDF and XPS files when certain fonts are used. Calibri is among the affected fonts, along with Cambria, Constantia and Corbel.
When the issue occurs, applications may fail with a System.IO.FileFormatException error.
Microsoft has provided a temporary workaround, but one of the available fixes disables a security protection introduced with the same update. If you want to avoid weakening system security, switching to an unaffected font is the safer temporary option.
Windows 11 WPF printing issue at a glance
| Area | Detail |
|---|---|
| Affected update | August 2026 .NET Framework cumulative update |
| Affected applications | Some WPF applications |
| Main error | System.IO.FileFormatException |
| Affected tasks | Printing and PDF or XPS generation |
| Known affected fonts | Calibri, Cambria, Constantia, Corbel |
| Known working alternatives | Arial, Times New Roman, Verdana, Tahoma, Segoe UI, Calibri Light |
| Temporary workaround | Change font or apply AppContext override |
| Security concern | AppContext workaround disables a protection added in the August update |
The issue appears to be specific to particular fonts rather than a general Windows printing failure.
That means the same WPF application may print normally when using one font but fail when the document switches to Calibri or another affected typeface.
Calibri is one of several fonts causing failures
Microsoft says the error can occur when WPF applications print content or create PDF and XPS files using certain fonts.
Calibri is the most notable because it remains widely used in documents and business applications.
Cambria, Constantia and Corbel can reportedly trigger the same behavior.
Several common alternatives do not reproduce the problem. Arial, Times New Roman, Verdana, Tahoma, Segoe UI and Calibri Light have been identified as working options in the supplied information.
For organizations that can change templates or document formatting temporarily, using one of those alternatives may be the simplest way to keep printing without changing security settings.
Microsoft offers an AppContext workaround
Microsoft has also provided an application configuration workaround for cases where changing the font is not practical.
The workaround requires adding an AppContext override to the application configuration file.
It uses the following switch:
Switch.MS.Internal.TtfDelta.DisableCmapAndSbitOverflowProtection=true
The setting can be placed inside the application’s runtime configuration.
However, there is an important tradeoff.
Enabling this switch disables protections introduced by the August 2026 update. That means the workaround restores compatibility by turning off part of the security behavior that caused the problem.
For that reason, changing the font is the better option if maintaining the update’s security protections is more important than preserving the original document formatting.
The issue also affects PDF and XPS creation
The bug is not limited to physical printers.
WPF applications can also fail when generating PDF or XPS content if an affected font is present.
That could create problems for business software that relies on WPF for report generation, invoices, forms, document export or other automated workflows.
In those environments, administrators may need to test affected applications carefully before applying the configuration workaround broadly.
Microsoft still needs to provide a permanent fix
The current solution is temporary.
Changing fonts avoids the problem but can affect document appearance, while the AppContext override restores compatibility at the cost of disabling a security protection.
A proper update would need to resolve the font handling problem without requiring either compromise.
Until Microsoft releases a permanent correction, the safest path is to use an unaffected font where possible.
If your WPF application depends specifically on Calibri, Cambria, Constantia or Corbel, the configuration override may keep printing and PDF or XPS generation working, but you should understand the security impact before enabling it.
Discussion (0)
Be the first to comment.