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

Microsoft has confirmed that the security update scheduled for April 2026 will include the psmounterex.sys driver in its Vulnerable Driver Blocklist. This change causes some third-party backup programs that depend on the driver for mounting images and creating VSS snapshots to fail. The block was introduced to fix CVE-2023-43896, a high-severity buffer overflow vulnerability that could allow privilege escalation or arbitrary code execution.