UMVA has learned that Microsoft’s May 2026 security update, KB5089549, is tripping a hidden snag on certain Windows 11 machines, leaving users staring at the dreaded 0x800f0922 error.
The culprit is a cramped EFI System Partition (ESP). When the partition’s free space dwindles to 10 MB or less, the update stalls during the reboot phase, hovering at roughly 35 % before rolling back with a cryptic “Something didn’t go as planned” message.
Logs in C:\Windows\Logs\CBS\CBS.log betray the truth, flashing entries like “SpaceCheck: Insufficient free space” and “ServicingBootFiles failed. Error = 0x70,” confirming the ESP’s capacity crisis.
This glitch is currently haunting Windows 11 versions 25H2 and 24H2, while Windows Server installations appear untouched.
For those unwilling to dive into system internals, Microsoft’s Known Issue Rollback (KIR) offers a safety‑net, reverting the machine to its pre‑update state with a single click.
Power users with admin rights can sidestep the problem by tweaking the registry. Opening an elevated Terminal and running the command reg add "HKLM\SYSTEM\CurrentControlSet\Control\Bfsvc" /v EspPaddingPercent /t REG_DWORD /d 0 /f forces the installer to ignore the ESP size limit, after which a reboot and retry often seal the deal.
Sources have confirmed to UMVA that a permanent fix is already in the works, destined to land in an upcoming Windows update and restore smooth sailing for all affected devices.
