KB5079391 — March 2026 Cumulative Update Preview for Windows 11

Overview

KB5079391 is a March 26, 2026 cumulative update preview for Windows 11 that delivers quality improvements and addresses multiple system stability issues. This optional preview update brings Windows 11 version 24H2 to Build 26200.8116 and Windows 11 version 23H2 to Build 26100.8116.

As a preview update, KB5079391 provides early access to fixes and improvements that will be included in the next monthly security update. This allows users and organizations to test changes in their environments before the mandatory security update release.

Affected Systems

This update applies to the following Windows 11 versions:

All editions of Windows 11 are supported, including Home, Pro, Pro Education, Pro for Workstations, Enterprise, and Education.

Issue Description

This cumulative update preview addresses several issues affecting Windows 11 systems:

• File Explorer crashes when navigating certain network locations
• Start menu search functionality returning incomplete results
• Windows Security notifications displaying incorrect status information
• Task Manager process details showing inaccurate memory usage statistics
• Windows Update service occasionally failing to check for updates automatically
• Bluetooth audio devices experiencing intermittent connection drops
• System performance degradation during high disk I/O operations

Root Cause

The issues addressed in KB5079391 stem from multiple components including file system drivers, search indexing services, security notification handlers, and system resource monitoring APIs. These problems were introduced through previous updates and affect core Windows 11 functionality across different system configurations.

Resolution — Key Fixes

1. Resolves File Explorer network navigation crashes

This update fixes a critical issue where File Explorer would crash when accessing certain SMB network shares or mapped drives. The fix addresses a memory allocation problem in the network file system driver that occurred when handling long file paths or special characters in network locations. Users will no longer experience unexpected File Explorer terminations when browsing network resources.

2. Improves Start menu search accuracy and performance

The update enhances the Windows Search indexing service to provide more accurate and complete search results in the Start menu. This includes fixes for missing file results, improved handling of recently modified documents, and better integration with cloud storage providers. Search response times are also improved by optimizing the indexing database queries.

3. Corrects Windows Security notification display issues

This fix addresses incorrect status reporting in Windows Security notifications, particularly for Windows Defender Antivirus and firewall status. The update ensures that security notifications accurately reflect the current protection state and eliminates false positive alerts about disabled security features when they are actually functioning correctly.

4. Fixes Task Manager memory usage reporting accuracy

The update resolves inaccurate memory usage statistics displayed in Task Manager's process details. This includes corrections to virtual memory calculations, working set measurements, and private bytes reporting. System administrators and users will now see accurate memory consumption data for better system monitoring and troubleshooting.

5. Enhances Windows Update service reliability

This fix improves the Windows Update service's ability to automatically check for and download updates. The update addresses timeout issues and connection failures that could prevent the service from contacting Microsoft's update servers. This ensures more consistent automatic update checking and reduces manual intervention requirements.

6. Resolves Bluetooth audio connectivity issues

The update includes improvements to Bluetooth audio device management, addressing intermittent connection drops and audio quality issues. This fix enhances the Bluetooth stack's handling of audio codecs and power management, resulting in more stable connections with headphones, speakers, and other audio devices.

7. Optimizes system performance during high disk I/O operations

This update improves system responsiveness during intensive disk operations by optimizing the I/O scheduler and memory management algorithms. Users will experience better system performance when copying large files, running disk-intensive applications, or performing system maintenance tasks like disk defragmentation.

Installation

KB5079391 is available as an optional preview update through Windows Update. To install this update:

Windows Update Installation

1. Open Settings > Windows Update
2. Click "Check for updates"
3. Under "Optional updates available," select KB5079391
4. Click "Download and install"

Microsoft Update Catalog

The update is also available for manual download from the Microsoft Update Catalog for enterprise deployment scenarios. The standalone package is approximately 847 MB for x64 systems and 654 MB for ARM64 systems.

Enterprise Deployment

System administrators can deploy KB5079391 through:

• Windows Server Update Services (WSUS)
• Microsoft System Center Configuration Manager (SCCM)
• Microsoft Intune
• Group Policy-based deployment

Prerequisites

No specific prerequisites are required for this update. However, ensure sufficient disk space is available (minimum 2 GB free space recommended).

Restart Requirements

A system restart is required to complete the installation of KB5079391.

Known Issues

Microsoft has identified the following known issues with KB5079391:

Windows Subsystem for Linux (WSL) Compatibility

Some users may experience issues with WSL2 distributions failing to start after installing this update. This affects systems running custom WSL configurations or third-party Linux distributions.

Workaround: Restart the WSL service using the command:

wsl --shutdown
wsl --distribution [DistributionName]

Third-Party Antivirus Compatibility

Certain third-party antivirus solutions may report false positives or experience compatibility issues with updated system files. This primarily affects older antivirus versions that have not been updated to recognize the new file signatures.

Workaround: Update antivirus definitions to the latest version or temporarily disable real-time scanning during the update installation.

Custom Start Menu Layouts

Organizations using custom Start menu layouts deployed through Group Policy may notice layout resets after installing this update. This affects environments with heavily customized Start menu configurations.

Workaround: Reapply Group Policy settings after the update installation completes.

Verification

To verify successful installation of KB5079391:

1. Open Settings > System > About
2. Verify the OS build number shows 26200.8116 (Windows 11 24H2) or 26100.8116 (Windows 11 23H2)
3. Alternatively, use PowerShell command: Get-HotFix -Id KB5079391