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Image Mounting or VSS Errors Following Recent Windows Updates

- Overview

- What Has Happened

- How This May Affect Users

- Systems Impacted

- Products affected

- Windows Versions

- Recommended actions if you experience Image Mounting issues

- Temporary Workarounds to use Image Mounting for Extracting Files

- Recommended actions if you experience VSS error message

Overview

Following Microsoft Windows security updates released on April 14, 2026, some customers may experience issues mounting backup images or may see VSS-related errors.

We are currently tracking two separate behaviours reported after these updates:

  1. A confirmed Code Integrity driver block affecting image mounting in Reflect 8 and Reflect LTSC
  2. A separate VSS-related issue that is currently under investigation

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 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:

Investigation into both behaviours is ongoing. We will continue to provide updates as additional information becomes available.

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.

Separately, some customers are reporting VSS timeout or VSS_E_BAD_STATE errors following the same Windows updates. These errors do not prevent backup images from being created. We are continuing to investigate these reports and do not currently believe they are directly related to the psmounterex.sys driver block.

How This May Affect Users

Important:

  • Backup creation continues to function
  • Image restores continue to function

Customers may experience one or more of the following symptoms:

  • 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)
  • VSS timeout or VSS_E_BAD_STATE errors may have a performance impact on backup image creation

Systems Impacted

Products Affected

  • Reflect 8
  • Reflect LTSC
  • Site Manager 8
  • Reflect X is not affected by the confirmed image mounting driver block, as it does not use the psmounterex.sys driver. Some customers may see VSS timeout issues.

Windows Versions

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

Recommended actions if you experience Image Mounting issues

We continue to investigate both behaviours. 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

Recommended actions if you experience VSS error message

We are investigating this issue. Please contact our support team and include the relevant error message(s) and any VSS logs available.