CyberNew CyberNew
Defensive Security & Blue Team BleepingComputer 1 month ago

Microsoft: August updates break printing, PDF export in WPF apps

CN
CyberNew Threat Research Desk
• Original Reporting: BleepingComputer
CyberNew Threat Intel Assessment
Assessed Severity: CRITICAL
Impacted Surface
Client Endpoints & Operating Systems
Intelligence Sector
Defensive Security & Blue Team

Analyst Takeaway

"Microsoft has confirmed that .NET Framework updates released as part of the August 2026 Patch Tuesday are breaking printing and PDF export in some applications. In a Windows release health alert seen by BleepingComputer, Microsoft says this known issue affects only apps that use the Windows Presentation Foundation (WPF) UI framework, an open-source graphical subsystem for building Windows desktop..."

Recommended Defense & Mitigation

  • Emergency Patching: Prioritize vendor patches and CVE mitigation across internet-facing assets immediately.
  • Perimeter Audit: Inspect perimeter firewall logs and hunt for unauthorized RCE indicators.
Curated & Verified by CyberNew Threat Intelligence Desk Standard Defense Framework (NIST / MITRE ATT&CK)

Printer

Microsoft has confirmed that .NET Framework updates released as part of the August 2026 Patch Tuesday are breaking printing and PDF export in some applications.

In a Windows release health alert seen by BleepingComputer, Microsoft says this known issue affects only apps that use the Windows Presentation Foundation (WPF) UI framework, an open-source graphical subsystem for building Windows desktop client applications.

"After installing the August 2026 .NET Framework cumulative update, some WPF applications may fail with a System.IO.FileFormatException when printing or generating PDF/XPS content that uses certain fonts, including Calibri," Microsoft says.

image

The complete list of impacted platforms includes both Windows client releases (including the latest versions of Windows 10 and Windows 11) and Windows Server (from Windows Server 2012 up to Windows Server 2025).

Microsoft says it is still investigating the issue and, until it can ship a permanent solution, has provided a temporary fix to help affected users work around these printing problems.

<configuration>
 <runtime>
   <AppContextSwitchOverrides
     value="Switch.MS.Internal.TtfDelta.DisableCmapAndSbitOverflowProtection=true"/>
 </runtime>
</configuration>
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Source Verification & Original Intelligence

This threat report was reviewed by CyberNew analysts and cross-referenced with primary security disclosures from BleepingComputer.

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