Windows 11 users have recently reported encountering ACPI.sys errors and Blue Screen of Death (BSOD) issues after installing the KB5058405 update. This critical system error, often displaying the stop code SYSTEM_THREAD_EXCEPTION_NOT_HANDLED or 0xc0000098, primarily affects virtual environments like Hyper-V and Azure Virtual Machines, though some physical systems have also been impacted. Here's a comprehensive guide to diagnosing and resolving these stability problems.

Understanding the KB5058405 Update Issue

The KB5058405 update, released as part of Microsoft's monthly security patches, was intended to address various security vulnerabilities and improve system performance. However, users began reporting system crashes shortly after installation, with error logs pointing to ACPI.sys (Advanced Configuration and Power Interface driver) failures. This driver is crucial for hardware communication and power management in Windows.

Common Symptoms

  • Frequent BSOD with ACPI.sys-related stop codes
  • System instability in virtualized environments (Hyper-V, Azure VMs)
  • Boot failures with error 0xc0000098
  • Event Viewer logs showing ACPI driver crashes

Root Cause Analysis

Microsoft has acknowledged the issue, tracing it to compatibility problems between the updated ACPI driver and certain firmware configurations. The problem appears most prevalent in:
- Systems with outdated UEFI/BIOS firmware
- Virtual machines with synthetic hardware configurations
- Hyper-V environments with specific power management settings

Step-by-Step Fixes for ACPI.sys Errors

1. Uninstall the Problematic Update (Temporary Solution)

For immediate stability:
1. Open Settings > Windows Update > Update history
2. Click Uninstall updates
3. Locate KB5058405 and select Uninstall
4. Reboot your system

2. Update Your System Firmware

Since this is fundamentally a driver-firmware compatibility issue:
1. Check your motherboard manufacturer's website for UEFI/BIOS updates
2. For Azure VMs, ensure you're using the latest VM generation
3. For Hyper-V, update integration components

3. Apply Microsoft's Official Workaround

Microsoft has released a known issue rollback (KIR) for this problem. To force the fix:
1. Open Registry Editor (regedit)
2. Navigate to:
HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\CurrentVersion\Svchost
3. Create a new Multi-String Value named LocalServiceAndNoImpersonation
4. Set its value to ACPI
5. Reboot your system

4. Clean Boot Troubleshooting

To isolate software conflicts:
1. Run msconfig
2. Under the Services tab, check Hide all Microsoft services
3. Click Disable all
4. Under the Startup tab, click Open Task Manager
5. Disable all startup items
6. Reboot and test stability

5. System Restore or In-Place Upgrade

For persistent issues:
- Use a System Restore point from before the update
- Perform an in-place upgrade by reinstalling Windows 11 while keeping files/apps

Preventing Future Update Issues

  1. Enable Update pause for 7 days after major updates
  2. Create system restore points before installing updates
  3. Monitor the Windows Health Dashboard for known issues

Enterprise Solutions

For IT administrators managing multiple affected systems:
- Deploy the fix via Group Policy:
Computer Configuration > Administrative Templates > Windows Components > Windows Update > Manage updates offered from Windows Update
- Use Windows Server Update Services (WSUS) to approve updates after testing

Microsoft is expected to release a permanent fix in an upcoming cumulative update. Until then, these workarounds should restore system stability for most users experiencing ACPI.sys errors after KB5058405 installation.