Microsoft has released a critical out-of-band cumulative update, KB5089573, for Windows 11 versions 25H2 and 24H2, resolving a widespread installation failure that blocked many users from receiving May 2026’s Patch Tuesday security updates. The update brings affected devices to OS builds 26200.8524 and 26100.8524 respectively.
The Problem: Patch Tuesday’s ESP Failure
The May 2026 Patch Tuesday update (KB5089549) introduced a critical regression that caused installation failures on a notable subset of Windows 11 devices. Affected systems reported error code 0x800f0922, with the update halting during the reboot phase at approximately 35–36% completion, leaving some devices in an inconsistent state.
The root cause was traced to devices with limited free space on the EFI System Partition (ESP) — specifically those with 10 MB or less of available space. The ESP is a dedicated partition on UEFI-based systems used to store bootloaders and critical startup files. When the Patch Tuesday update attempted to write additional files to this partition during the install process, the lack of space caused the operation to abort mid-reboot.
Microsoft initially issued a Known Issue Rollback (KIR) as a temporary measure, which automatically pushed relief to consumer and non-managed business devices without any administrator action. For enterprise environments, a separate registry-based workaround was made available — modifying the EspPaddingPercent value under HKLM\SYSTEM\CurrentControlSet\Control\Bfsvc — to temporarily mitigate the issue while a permanent fix was prepared.
What KB5089573 Fixes and Delivers
Released on May 26, 2026, KB5089573 permanently resolves the ESP space issue, eliminating the need for both the KIR rollback and the registry workaround. Beyond the critical fix, this update is a full production-quality cumulative update that delivers several additional components:
- AI Component Refresh: Image Search, Content Extraction, Semantic Analysis, and Settings Model are all updated to version 1.2605.856.0, reflecting Microsoft’s continued investment in on-device AI capabilities within Windows 11.
- Personalization Improvements: Added as part of the gradual rollout phase on May 28, 2026.
- Servicing Stack Update (KB5092734): Build 26100.8519 improves the reliability of the Windows update infrastructure, ensuring devices can cleanly receive future patches without similar partition-related failures.
How to Install KB5089573
The update is available through multiple channels and requires no additional prerequisites beyond running a compatible Windows 11 25H2 or 24H2 device:
- Navigate to Start → Settings → Windows Update → Advanced options → Optional updates and select the available update.
- Download the standalone package directly from the Microsoft Update Catalog using the KB number KB5089573.
- Enterprise environments can deploy the update via Windows Update for Business or WSUS (Windows Server Update Services).
Microsoft has confirmed there are no known issues with KB5089573 at the time of release.
Removal Considerations
Should removal be necessary after installation, administrators should use the DISM /online /get-packages command to identify the package name, followed by the DISM/Remove-Package option with the LCU package name as the argument. Notably, running the Windows Update Standalone Installer (wusa.exe) with the /uninstall switch will not work, as the combined package includes the Servicing Stack Update (SSU), which cannot be removed post-installation. Microsoft strongly advises against removing security updates given the inherent exposure risks.
Recommended Action
Given the widespread impact of the ESP space issue, which affected enterprise fleets, consumer devices, and managed business endpoints alike, IT administrators and end users should prioritize installing KB5089573 during their next maintenance window. Organizations that implemented the registry-based workaround should verify that the permanent fix has been successfully applied and remove any temporary modifications that were put in place as interim mitigation.
This update underscores the importance of monitoring Microsoft’s release health dashboard and Known Issues page after each Patch Tuesday cycle, as installation-level regressions — while relatively rare — can impact security posture when critical updates fail to apply correctly.