psmounterex.sys Archives

Winsage

May 10, 2026

Microsoft Confirms KB5083769 Breaks Macrium and Acronis Backups

Microsoft's April 2026 Windows security update, KB5083769, may disrupt image-mount operations for backup applications such as Macrium Reflect, Acronis Cyber Protect Cloud, UrBackup Server, and NinjaOne Backup due to the addition of the psmounterex.sys kernel driver to its Vulnerable Driver Blocklist. This action was taken to address a high-severity buffer overflow vulnerability, CVE-2023-43896. The inclusion of this driver in the blocklist has rendered several backup products inoperable, and Microsoft will not retract the block for security reasons. Administrators can use Event ID 3077 in the Code Integrity log to confirm that the blocklist is causing the failures. Microsoft advises updating backup applications to versions that include necessary driver protections instead of uninstalling or pausing the security patch. Additionally, the April updates have caused other issues, such as failures in Windows Server installations and devices booting into BitLocker recovery mode.

Winsage

May 8, 2026

Windows update is breaking backups, and here’s how you can fix it

A recent Windows update, KB5083769, released on April 14, 2026, blocks the psmounterex.sys driver, disrupting the functionality of third-party backup software like Acronis Cyber Protect Cloud, Macrium Reflect, and NinjaOne. This driver is essential for loading and mounting backup storage images. Users may encounter errors related to Microsoft VSS during backup attempts. The update is a security enhancement, not a bug, and users are advised to upgrade their backup software to versions that use a newer driver or temporarily uninstall the KB5083769 update. It is recommended to check for updates from the backup software provider and pause Windows Updates to prevent automatic reinstallation of the problematic update until a fix is available.

Winsage

May 7, 2026

My Windows 11 backup broke after KB5083769 — Microsoft says this simple fix might save your files

The Windows 11 security update KB5083769, released on April 14, 2026, introduces changes to the psmounterex.sys driver, causing compatibility issues with third-party backup solutions such as Macrium Reflect, Acronis Cyber Protect Cloud, UrBackup Server, and NinjaOne Backup. Microsoft states this is a necessary security adjustment, not a bug. The update also adds known vulnerable kernel drivers to a blocklist to enhance system security. Users can check if a driver is blocked by using the Event Viewer and looking for Event ID 3077 associated with a specific Policy ID.

Winsage

May 5, 2026

April 2026 Windows Update Breaks Third-Party Backup Software by Blocking Vulnerable Driver

Microsoft will include the psmounterex.sys driver in its Vulnerable Driver Blocklist in the April 2026 security update, affecting third-party backup applications that use this driver for image mounting and Volume Shadow Copy Service (VSS) snapshots. This decision addresses CVE-2023-43896, a critical buffer overflow vulnerability. Affected software includes Macrium Reflect, Acronis Cyber Protect Cloud, UrBackup Server, and NinjaOne Backup on Windows 11, Windows 10, and Windows Server platforms. Users may face issues during image-mount operations, receiving error messages related to VSS timeouts and Code Integrity errors in the Event Viewer. To check if a system is affected, users can look for Event ID 3077 in the Code Integrity Operational log. Microsoft recommends upgrading to newer versions of backup applications that do not use blocked drivers and advises against uninstalling or delaying the April update. Additionally, the update may cause certain Windows Server 2025 devices to boot into BitLocker recovery mode and has led to out-of-band updates for Windows Server update failures and restart loops on domain controllers.

Winsage

May 5, 2026

Defender yanks root certs as Windows updates blocks backups

Microsoft's Defender anti-malware tool update version 1.449.425.0 removed two DigiCert root digital certificates, leading to false positives that flagged them as severe malware (Trojan:Win32/Cerdigent.A!dha). This incident was later identified as a false positive, and updating to version 1.449.430.0 or later reinstates the certificates. The issue may be linked to a DigiCert employee encountering disguised malware. Additionally, Windows updates from April 14 caused third-party backup applications to malfunction due to the addition of vulnerable psmounterex.sys kernel driver versions to a blocklist. Users experienced difficulties with mounting backup image files, and Microsoft referenced a vulnerability rated 9.3 out of 10 in the driver. Other affected software includes Acronis Cyber Protect Cloud and UrBackup server. Microsoft has not explained the delay in adding the vulnerable driver to the blocklist, and other recent update-related issues have also been reported.

Winsage

May 4, 2026

Microsoft confirms April Windows updates cause backup failures

Microsoft has acknowledged that the April 2026 security updates have disrupted the functionality of various third-party backup applications using the psmounterex.sys driver, raising concerns among users. The issue primarily affects software leveraging the Volume Shadow Copy Service (VSS) snapshots, leading to failures due to VSS service timeouts. Notable impacted products include Macrium Reflect, Acronis Cyber Protect Cloud, UrBackup Server, and NinjaOne Backup, used on Windows 11, Windows Server, and Windows 10 devices. Disruptions can manifest as failures to mount backup image files, errors or timeouts when browsing or restoring from backup images, and error messages related to VSS timeouts. Microsoft updated its support documentation to clarify that the April updates included a security hardening change that added psmounterex.sys to the vulnerable driver blocklist to protect against a high-severity buffer overflow vulnerability (CVE-2023-43896). Affected users are advised to upgrade to newer application versions with updated drivers and not to uninstall or pause the security update. Users can check if the Microsoft Vulnerable Driver Blocklist is blocking a driver by looking for Event ID 3077 in the Code Integrity Operational log. Additionally, Microsoft has alerted users that some Windows Server 2025 devices may boot into BitLocker recovery mode after installing the KB5082063 update and has issued out-of-band updates to address installation failures and restart loops affecting Windows Server systems after the April 2026 updates.