KB5071876: fixed Skype for Business OWA integration fails after enabling the Dedicated Hybrid Application

Description of the security update for Microsoft Exchange Server Subscription Edition RTM: December 9, 2025 (KB5071876)

This security update resolves vulnerabilities in Microsoft Exchange Server. To learn more about these vulnerabilities, see the following Common Vulnerabilities and Exposures (CVE)

• ​​​​​​​​​​​​​​CVE-2025-64666 - Microsoft Exchange Server Elevation of Privilege Vulnerability
• CVE-2025-64667​​​​​​​ - Microsoft Exchange Server Spoofing Vulnerability

Issues that are fixed in this update

• ​​​​​​​Skype for Business OWA integration fails after enabling the Dedicated Hybrid Application

Exchange Server Health Checker

• To verify that that the installation is successful, and check whether any additional actions are required, run the Exchange Server Exchange Server Health Checker.

Enabling Extended Protection in Exchange Server

• To enable Extended Protection on Exchange-based servers, see Extended Protection enabled in Exchange Server (KB5017260).