January 2026 CU for SharePoint Server 2019: Key Considerations for Enterprise Environments

January 2026 CU for SharePoint Server 2019: Key Considerations

Microsoft has released the January 2026 Cumulative Update (CU) for SharePoint Server 2019. This update includes critical fixes to enhance the security and performance of your SharePoint environment. However, a specific issue requires attention before installation, particularly for enterprise environments.

Important: Addressing the NT Authority\System Account Issue

If your SharePoint farm is currently at the September 2025 CU patch level, you must remove the NT Authority\system account from the WSS_WPG and IIS_IUSRS local security groups on your SharePoint servers before applying the January 2026 CU. Failure to do so will cause the SharePoint fixes to fail during installation. Refer to this Microsoft article for detailed instructions.

Pre-Update Checklist for Enterprise Architects

Before deploying the January 2026 CU in your enterprise environment, consider the following:

• Verify Current Patch Level: Confirm the current CU version of your SharePoint farm.
• Address NT Authority\System: If on September 2025 CU, remove the account from the specified security groups.
• Comprehensive Backup: Perform a full backup of your SharePoint farm.
• Communication Plan: Notify users about the planned downtime and update schedule.
• Testing Environment: Deploy the CU to a test environment first to validate functionality and compatibility with existing customizations.

Post-Update Validation

After the update is complete:

• Verification: Confirm successful installation across all servers.
• Functionality Testing: Thoroughly test core SharePoint functionality and any custom solutions.
• Configuration Review: Reapply any custom configurations or settings as needed.

By following these steps, you can ensure a smooth and successful deployment of the January 2026 CU for SharePoint Server 2019, mitigating potential risks and maximizing the benefits of the update.