Image Mounting Errors Following April 2026 Windows Updates

- Temporary Workarounds to use Image Mounting for Extracting Files

Overview

Following Microsoft Windows security updates released on April 14, 2026, some customers using unsupported versions of Marcium products, may experience issues mounting backup images.

We are currently tracking the following behavior following these updates:

A confirmed Code Integrity driver block affecting image mounting in Reflect 8 and Reflect LTSC

The confirmed image mounting issue relates to Microsoft’s updated Vulnerable Driver Blocklist enforcement and impacts the psmounterex.sys driver used by Reflect 8 and Reflect LTSC (now resolved) for image mounting functionality.

Reflect X is not affected by the confirmed image mounting driver block because it does not use the psmounterex.sys driver. Reflect 8 is an end-of-life product and no longer receives feature development or ongoing security updates.

Status:

The image mounting issue relates to Microsoft’s updated Vulnerable Driver Blocklist enforcement and impacts the psmounterex.sys driver. Macrium Reflect LTSC has been updated to use the same image mounting mechanism as Macrium Reflect X, which does not make use of the psmounterex.sys driver.

What Has Happened

Microsoft’s April 2026 Windows security update (KB5083769) introduced stricter Code Integrity enforcement, which blocks the psmounterex.sys driver used by Reflect 8, Reflect LTSC, and SiteManager 8 for image mounting functionality.

Macrium had previously remediated the associated vulnerability in 2023. However, Microsoft’s newer enforcement model now blocks affected implementations of the driver regardless of prior remediation status.

This behaviour affects image mounting functionality only and does not impact core backup or restore operations.

How This May Affect Users

Important:

Backup creation continues to function
Image restores continue to function

Customers may experience the following symptom:

Inability to mount backup images as virtual drives, preventing image contents from being browsed in Windows Explorer (to confirm the image mounting issue described above, Windows Event Viewer may show Code Integrity Event ID 3077 entries indicating the psmounterex.sys driver has been blocked)

Systems Impacted

Products Affected

Reflect 8
Reflect LTSC was affected. A fix has been released and updating to the latest version will resolve the issue.
Site Manager 8
Reflect X is not affected by the confirmed image mounting driver block, as it does not use the psmounterex.sys driver.

Windows Versions

Windows 11 (24H2, 25H2)
Windows Server 2019, 2022, 2025

Recommended actions if you experience Image Mounting issues

We continue to investigate this behavior. In the meantime, we recommend:

Avoid installing Windows updates KB5083769 or KB5083631 where possible
If already installed and image mounting is business critical, consider temporarily uninstalling the update
Reflect 8 customers should upgrade to Reflect X where possible, as Reflect 8 is end of life and does not receive any feature development or security updates.
Site Manager 8 customers should upgrade to SiteManager Platform where possible, as Site Manager 8 is end of life

Important:

Uninstalling Windows security updates may reduce system security protections. Customers should assess this against their own operational and security requirements.

Temporary Workarounds to Use Image Mounting for Extracting Files

The following temporary workarounds may allow access to backup contents:

Use viBoot / VHDX-Based Access

Create a virtual machine from the backup image
Access files via attached VHDX storage
The VM does not need to be fully booted

Restore to Alternate Environment

Restore the backup to:
- Spare hardware
- Alternate environment
Extract required files from the restored system