Microsoft’s August Updates Causes Disruption

Overview

Microsoft has confirmed that the August 2026 Patch Tuesday .NET Framework updates are causing printing and PDF export failures in applications built with the Windows Presentation Foundation (WPF). The issue arises when certain fonts—such as Calibri—are used, leading to System.IO.FileFormatException errors during printing or PDF/XPS generation.

Impacted Platforms

The problem affects:

• Windows 10 (latest versions)
• Windows 11 (latest versions)
• Windows Server (2012 through 2025)

Only WPF applications are impacted, meaning other .NET apps remain unaffected.

Workaround Provided

Microsoft has shared a temporary fix:

xml

<configuration>
 <runtime>
   <AppContextSwitchOverrides
     value="Switch.MS.Internal.TtfDelta.DisableCmapAndSbitOverflowProtection=true"/>
 </runtime>
</configuration>

This workaround disables protections introduced in the August update, which means it should only be used as a short‑term measure. Microsoft warns that applying it may expose systems to vulnerabilities addressed by the patch.

Security vs. Usability

This situation highlights the trade‑off between security and functionality:

• Temporary workaround restores printing/PDF export but weakens protections.
• Permanent fix pending: Microsoft is investigating and will release a long‑term solution.

Historical Context

This isn’t the first time WPF updates have caused disruption:

• In February 2021, cumulative updates caused WPF apps and Visual Studio crashes.
• In August 2026, Microsoft also acknowledged gaming issues (ARC Raiders, MARVEL Tōkon: Fighting Souls, The Finals) linked to Windows 11 updates.

Guidance for Developers & IT Teams

• Apply workaround cautiously: Only if printing/PDF export is business‑critical.
• Monitor Microsoft’s release health dashboard: Stay updated on permanent fixes.
• Test applications: Validate functionality before deploying updates widely.
• Balance risk: Consider whether disabling protections is worth the exposure.

Expert in the Cloud Insight

This incident underscores how patches can inadvertently disrupt core business workflows. For enterprises relying on WPF apps, the lesson is clear: always test updates in staging environments before production rollout. Security fixes are essential, but usability failures can be just as disruptive if they halt printing or document generation.