SharePoint Server March 2026 PU: Security Fixes and Installation Considerations

SharePoint Server March 2026 PU: Key Security Updates Released

Microsoft has released the March 2026 Public Update (PU) for SharePoint Server. This update addresses critical security vulnerabilities and includes improvements aimed at enhancing the overall stability and performance of your SharePoint environment. The update is distributed via Microsoft Update, simplifying the installation process.

Security is paramount for SharePoint, a platform that often hosts critical business processes. Vulnerabilities can have severe consequences, making timely security updates essential.

Critical Consideration After September 2025 CU

If your SharePoint servers already have the September 2025 Cumulative Update (CU) installed, you need to be aware of a potential issue before installing the March 2026 PU. An incompatibility related to the permissions of the NT Authority\system account and the IIS_IUSRS local security groups on SharePoint servers has been identified following the September 2025 CU. This incompatibility can cause the update process to fail.

Workaround: Before installing the March 2026 PU, temporarily remove the NT Authority\system account and the IIS_IUSRS local security groups from the WSS_WPG group and relevant file system permissions on all SharePoint servers. After the update is successfully completed, you can re-add these accounts and groups.

Failure to take this step can lead to errors during the update process and potentially destabilize your SharePoint environment. Therefore, it’s crucial to heed this warning and perform the necessary checks before installation.

Best Practices for SharePoint Updates

SharePoint updates require careful planning and execution. Here’s a breakdown of the recommended steps for a successful update:

1. Pre-Update Backup: Before starting the update process, create a full backup of all your SharePoint databases and configuration files. This allows you to restore your system to its previous state in case of any issues.
2. Test Environment Staging: Test the update in a staging environment before applying it to production. This helps you identify potential issues and develop solutions in advance.
3. Detailed Update Plan: Plan the update process meticulously, including the timing and methodology. Choose a suitable time window to minimize potential disruptions during the update.
4. Monitoring and Validation: After the update is complete, carefully monitor your SharePoint environment to ensure everything is functioning correctly. Collect user feedback to identify any potential issues.

Simplified Installation via Microsoft Update

The availability of the March 2026 PU through Microsoft Update significantly simplifies the installation process. Microsoft Update automatically downloads and installs updates for your Windows Server operating system, eliminating the need to manually download and install updates.

However, even when using Microsoft Update, caution is advised. If you don’t want updates to be installed automatically, you can configure Microsoft Update settings to approve updates manually. This allows you to test updates in a staging environment before deploying them to production.

Conclusion

The SharePoint Server March 2026 PU is an important update that enhances the security and stability of your SharePoint environment. Those who have already installed the September 2025 CU should pay close attention to the steps outlined above before proceeding with the installation. By carefully planning and executing the update process, you can ensure the smooth operation of your SharePoint environment.

Remember, applying security updates promptly is one of the most important steps you can take to protect your SharePoint environment and data. Therefore, I recommend applying this update as soon as possible.

For more information and details about the updates, you can visit Stefan Goßner's blog post.