Microsoft’s April 2026 cumulative security update for Windows 11 is causing widespread disruptions for users and enterprises relying on third-party backup software, prompting security patch analyst Susan Bradley at AskWoody to issue an MS-DEFCON level 3 advisory, a clear signal for IT administrators to hold off deployment until a fix arrives.
The problematic update, KB5083769, targets Windows 11 versions 24H2 and 25H2 (OS Builds 26200.8246 and 26100.8246) and was released on April 14, 2026.
At the heart of the issue lies a critical regression in Microsoft’s Volume Shadow Copy Service (VSS), the Windows component responsible for snapshot-based backup and restore operations, relied upon by a broad range of enterprise and consumer backup solutions.
When VSS malfunctions, backup jobs either stall entirely or terminate with timeout errors, leaving systems without scheduled backup coverage. For enterprise environments where data continuity is non-negotiable, this represents a serious operational and compliance risk.
Affected Backup Vendors
Several major third-party vendors have already confirmed the impact:
- UrBackup — File backups are failing after installing the update; the vendor recommends uninstalling KB5083769 for affected users
- Macrium Reflect — VSS-related failures are being actively reported across community forums, with an investigation currently underway.
- Acronis Cyber Protect Cloud — Backup jobs are failing with the specific error: “Microsoft VSS has timed out during snapshot creation”; Acronis officially recommends uninstalling the update and rebooting affected systems
It is worth noting that not all backup solutions are impacted. Microsoft’s native Windows 11 cloud-based Backup feature does not depend on VSS and continues to function normally.
The VSS component also underpins 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 particular front. Still, the regression nonetheless signals fragility in a foundational system component ahead of its planned rollout.
Mitigation Steps
For users already experiencing backup failures, the following rollback procedure is advised:
- Navigate to Settings → Windows Update → Update History
- Scroll to Related Settings and click Uninstall Updates
- Locate Security Update for Microsoft Windows (KB5083769)
- Click Uninstall and allow the system to reboot
- Return to Windows Update and Pause Updates to prevent automatic reinstallation
Before proceeding, confirm whether your specific backup solution is affected by checking your vendor’s official support channels and community forums.
The MS-DEFCON 3 designation from Susan Bradley at AskWoody advises administrators to delay deploying KB5083769 in production environments until Microsoft delivers a remediation.
A patch addressing the VSS regression is anticipated either as an out-of-band release or as part of the May 2026 cumulative update cycle.
Organizations should prioritize reviewing their backup job logs immediately and implement rollback procedures on any system showing snapshot or VSS-related failures to avoid unprotected backup windows.
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