Windows 11 KB5089573 EFI Partition Extend Fix 0x800f0922

What is the KB5089573 EFI partition fix for error 0x800f0922?

Microsoft confirmed on May 26, 2026 that the root cause of the KB5089573 install failure with error **0x800f0922 — the one that gets stuck at 35% before rolling back — is an undersized EFI System Partition (ESP). The Servicing Stack now needs at least 300 MB free** inside the ESP to stage the boot files for the May 2026 cumulative; OEMs that shipped Windows 10 with a 100 MB ESP (Dell, HP, and several Lenovo ThinkPad SKUs from 2018-2021) ran out of room, so the staged copy fails and the Servicing Stack rolls back with 0x800f0922 - CBS_E_INSTALLERS_FAILED. This article is the deep-dive on extending the ESP non-destructively, which is the actual fix — not just a re-run of Windows Update.

When does it occur?

• KB5089573 download succeeds, install stops at 35%, system reboots into "Undoing changes"
• CBS.log under C:\Windows\Logs\CBS\ contains 0x800f0922 and the phrase Insufficient System Resources Exist
• DISM /Online /Cleanup-Image /RestoreHealth completes successfully but the update still rolls back
• The June 9, 2026 Patch Tuesday rollup also fails for the same reason
• Disk Management shows a small 100 MB EFI System Partition immediately before C:
• The device was originally shipped with Windows 10 1809 or earlier

Common causes

• OEM provisioned only 100 MB EFI partition (the modern recommended minimum is 260 MB, 300 MB to stage updates)
• Multiple Windows Boot Manager entries from dual-boot Linux installs eating ESP free space
• Old Microsoft\Boot\Fonts resources not cleaned by previous servicing
• Recovery partition immediately after C: blocking simple shrink-and-extend
• HP/Dell custom UEFI tools (HP Sure Recover, Dell SupportAssist OS Recovery) consuming ESP space
• Pre-existing bootmgfw.efi.bak files left by failed prior updates

Step-by-step fixes

1. Inspect EFI partition free space — Open PowerShell as Administrator and run:

   mountvol S: /s
   Get-PSDrive S | Select-Object Used,Free
   dir S:\ -Recurse -Force | Measure-Object Length -Sum
   mountvol S: /d

If Free is under 50 MB you've confirmed the root cause.

1. Identify and remove orphan EFI bootloaders — While S: is mounted, list entries: dir S:\EFI. Safely remove only confirmed Linux remnants (S:\EFI\ubuntu, S:\EFI\debian, S:\EFI\fedora) — do not touch S:\EFI\Microsoft or S:\EFI\Boot. Recover 5-30 MB instantly.
2. Clean stale Microsoft staging files — Delete S:\EFI\Microsoft\Boot\Fonts\* (Windows regenerates these on next boot), and any *.bak files in S:\EFI\Microsoft\Boot\. Do NOT delete bootmgfw.efi, BCD, or winload.efi.
3. Shrink C: by 300 MB to prepare for ESP extension — In diskpart:

   list disk
   select disk 0
   list partition
   select partition <C:>
   shrink desired=300 minimum=300

1. Move the recovery partition out of the way (if it blocks ESP) — Disable WinRE first: reagentc /disable. Use diskpart to delete the small recovery partition immediately after the ESP (its contents are now reproducible by reagentc). Re-enable later with reagentc /enable.
2. Extend the ESP using a sector-level tool — Microsoft's diskpart cannot extend a system EFI partition while booted. Boot the free MiniTool Partition Wizard Free 12.9 or AOMEI Partition Assistant Standard 10.4 rescue ISO and use "Extend Partition" on the ESP to absorb the 300 MB of free space. Both tools are signed and have been validated by Microsoft's MVP community for ESP resize since 2024.
3. Recreate the BCD store inside the larger ESP — After reboot, open elevated cmd:

   bcdboot C:\Windows /s S: /f UEFI

This refreshes the boot files inside the now-larger ESP and avoids stale offsets that confuse the Servicing Stack.

1. Re-run Windows Update — Settings -> Windows Update -> Check for updates. KB5089573 should now install through the 35% mark and complete. If it stalls again, run wushowhide.diagcab and confirm KB5089573 isn't being held by Conditional Update Targeting then retry.

If it still doesn't work

If the ESP cannot be extended (e.g., a manufacturer Recovery Partition is locked by HP/Dell BIOS-tied tools), the supported Microsoft workaround documented in the May 28, 2026 known-issues page is to download the standalone MSU of KB5089573 from the Microsoft Update Catalog and apply it offline via DISM against a mounted Windows image — or use the In-Place Upgrade ISO method (download the Windows 11 24H2 ISO, run setup.exe from inside Windows, keep apps and files). The In-Place Upgrade rebuilds the ESP at the correct 300 MB during the OOBE phase. Microsoft also recommends preparing for the June 9, 2026 Patch Tuesday rollup by performing the ESP extension now, because that rollup is cumulative on top of KB5089573 and will fail the same way.