What failed: KB5089549 installations and the 0x800f0922 rollback
Microsoft identified and has now resolved a known installation failure tied to the May 2026 Windows 11 security update, KB5089549. Impacted devices reported the error code 0x800f0922 and showed the familiar rollback message, "Something didn't go as planned. Undoing changes." Log entries such as "SpaceCheck" and "ServicingBootFiles failed" pointed administrators to insufficient free space on the EFI System Partition (ESP) as the cause. Microsoft said the update could proceed through initial steps but commonly failed during the reboot phase, around 35–36% completion.
How Microsoft fixed it: KB5089573 and its rollout
On May 26, 2026, Microsoft released a preview cumulative update, KB5089573, for Windows 11 versions 25H2 and 24H2 that included a resolution for the ESP free-space installation failures. The company says the issue "was resolved by Windows updates released May 26, 2026 (KB5089573), and later" and recommends installing the latest update because it "contains important improvements and issue resolutions, including this one." Microsoft also said the fix will be made available to all users who install the June Patch Tuesday updates later in the month.
Workarounds and administrative mitigations: Known Issue Rollback and Group Policy
For users who prefer not to install the May 26 optional preview update, Microsoft points to Known Issue Rollback (KIR) as a mitigation. KIR is a Windows feature that can reverse buggy updates pushed via Windows Update, allowing affected systems to avoid or recover from problematic changes without applying the preview cumulative update. In managed enterprise environments, administrators can manually mitigate the problem by installing and configuring a specific Group Policy; Microsoft provides guidance on deploying Known Issue Rollback group policies on its support website. Microsoft advised that "If you install an update released May 26, 2026 (KB5089573) or later, you do not need to use a workaround. If you are using an update released before this date, and are experiencing this issue, you can use the following workaround."
Which Windows builds and changes were involved
KB5089573 was issued as a preview cumulative update for Windows 11 versions 25H2 and 24H2 and included 30 changes, among them performance and reliability improvements. Microsoft’s description links the ESP-space failure specifically to devices with limited EFI System Partition free space — calling out devices with 10 MB or less available as particularly susceptible to the rollback behavior.
How enterprises, administrators, and end users are affected
- Administrators and IT managers: Those running Windows 11 25H2 or 24H2 who saw installations fail with 0x800f0922 can deploy KB5089573 or the June cumulative rollup to resolve the issue, or deploy Known Issue Rollback via Group Policy as a targeted mitigation for managed fleets.
- End users and help desks: Devices that showed "Something didn't go as planned. Undoing changes." during KB5089549 installs — and logs showing "SpaceCheck" or "ServicingBootFiles failed" — should either install the May 26 update (or later) or follow Microsoft's workaround guidance until the fix is applied.
Broader patching context from Microsoft in May–June 2026
Microsoft’s advisory comes amid a broader set of update-related fixes earlier in the month: the company confirmed that April 2026 security updates caused failures in third-party backup applications that relied on a vulnerable driver, and it also fixed a Windows Autopatch bug that caused driver updates, which were restricted by administrative policies, to be deployed on some Autopatch-managed Windows devices across the European Union. The KB5089573 preview shipped as part of this sequence of corrective updates.
For affected systems the practical path is clear: install KB5089573 or later (or the forthcoming June updates), or apply Known Issue Rollback via the Group Policy guidance Microsoft provides. The sequence underlines how a relatively small resource — 10 MB of free space on an EFI partition — can cascade into visible installation failures for widely distributed updates, and how Microsoft is using both cumulative patches and rollback tooling to unstick affected devices.
