December 2025 CU for SharePoint Server Subscription Edition: Key Considerations

December 2025 CU for SharePoint Server Subscription Edition: Key Considerations

Microsoft has released the December 2025 Cumulative Update (CU) for SharePoint Server Subscription Edition. This update includes fixes and improvements designed to enhance the stability and security of your SharePoint environment. Before proceeding with the installation, it's crucial to understand a potential issue that may arise, especially if you're updating from the September 2025 CU.

Critical Note: If your current farm patch level is the September 2025 CU, you must remove the NT Authority\system account from the WSS_WPG and IIS_IUSRS local security groups on your SharePoint servers. Failure to do so will cause the SharePoint fixes to fail during installation. For detailed information on this issue, refer to this article.

Pre-Installation Checklist

• Verify your current farm patch level.
• If you have the September 2025 CU installed, remove the NT Authority\system account from the specified security groups.
• Create a backup of your SharePoint farm before initiating the update process.

Post-Installation Steps

• Confirm that the update has been successfully installed.
• Thoroughly test your SharePoint environment to ensure proper functionality.

Applying this CU is essential for maintaining the security and performance of your SharePoint environment. We recommend applying it as soon as possible, paying close attention to the pre-installation requirements.