A recent update to Windows, specifically KB5083769, has introduced a security feature that inadvertently disrupts the functionality of various third-party backup software. Released on April 14, 2026, this update blocks the psmounterex.sys driver, which is essential for loading and mounting backup storage images. While this may seem alarming, a straightforward solution is available for users affected by this change.
How to prevent the latest Windows update from breaking third-party backup software
Many popular backup solutions, including Acronis Cyber Protect Cloud, Macrium Reflect, and NinjaOne, rely on creating disk images rather than simply copying files for data protection. These applications utilize the psmounterex.sys filesystem driver to facilitate the mounting and restoration of these disk images.
However, the recent update has flagged the psmounterex.sys driver, either due to its presence on a vulnerable driver blocklist or because its signature has been revoked. This action effectively prevents third-party backup software from accessing and mounting backup disk images. Users of Acronis Cyber Protect Cloud, for instance, may encounter the following error message:
“The backup has failed because Microsoft VSS has timed out during the snapshot creation or VSSEBAD_STATE.”
It’s important to note that this situation is not a bug; rather, it is a security enhancement aimed at safeguarding critical system files from potentially corrupt or infected drivers. Consequently, the resolution does not rest solely with Microsoft. The company recommends that users either upgrade their backup software to a version that employs a newer driver, thereby replacing the outdated psmounterex.sys, or temporarily uninstall the KB5083769 update until the software vendor provides a suitable fix.
To address this issue, users should first check the website of their backup software provider for any available updates and install them. This step should resolve the error for most users. If the updated software still lacks a new driver or if no updates are available, temporarily uninstalling the KB5083769 update may be necessary. Additionally, it is advisable to pause Windows Updates to prevent this particular update from reinstalling automatically until the software developers release an updated version of their backup application. Once an update is available, users can download and install it to restore full backup functionality.
