Microsoft Windows 11 April 2026 Security Update Breaks Third-Party Backup Applications

Microsoft’s April 2026 cumulative security update for Windows 11 is causing significant disruptions for users relying on third-party backup software, triggering an MS-DEFCON level 3 advisory from security patch analyst Susan Bradley at AskWoody.

The problematic update, KB5083769, applies to Windows 11 versions 24H2 and 25H2 (OS Builds 26200.8246 and 26100.8246), released on April 14, 2026.

At the root of the issue is a malfunction in Microsoft’s Volume Shadow Copy Service (VSS) a critical Windows component that enables snapshot-based backup and restore operations across a wide range of enterprise and consumer backup solutions.

When VSS fails, backup jobs either stall or terminate with timeout errors, leaving systems without scheduled backup coverage a serious risk for both individual users and enterprise environments.

Affected Vendors

Multiple third-party vendors have already acknowledged the problem:

• UrBackup — File backups are failing post-update; the vendor recommends uninstalling KB5083769 for impacted users
• Macrium Reflect — VSS-related failures reported in active Reddit community threads; investigation underway
• Acronis Cyber Protect Cloud — Backup jobs failing with the error “Microsoft VSS has timed out during snapshot creation”; Acronis recommends uninstalling the update and rebooting

It is important to note that not all backup solutions are affected. Microsoft’s native Windows 11 cloud-based Backup feature does not rely on VSS and remains unaffected.

The VSS component is also foundational to Microsoft’s forthcoming Point-in-Time Restore (PITR) feature for Windows 11, first previewed during Microsoft Ignite in November 2025 via Insider build KB5070307.

Since PITR has not yet reached general availability, most standard users face no additional risk from that front.

Mitigation Steps

For users experiencing backup failures after installing KB5083769, the following rollback procedure is advised:

1. Navigate to Settings → Windows Update → Update History
2. Scroll to Related Settings and click Uninstall Updates
3. Locate Security Update for Microsoft Windows (KB5083769)
4. Click Uninstall and allow the system to reboot
5. Return to Windows Update and Pause Updates to prevent reinstallation

Before uninstalling, verify whether your specific backup solution is impacted by checking your vendor’s official support channels and forums.

MS-DEFCON 3 signals that administrators should hold off on deploying KB5083769 in production environments until Microsoft issues a fix, Susan Bradley at AskWoody said.

A patch addressing the VSS regression is anticipated in an upcoming out-of-band or May 2026 cumulative update.

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