microsoft has confirmed that the windows 11 May 2026 Security update KB5089549released on May 12, it does not install on some devices running versions 24H2 and 25H2. The installation often fails during the reboot process, usually around 35 percent, and displays error code 0x800f0922. On affected systems, the update is rolled back and displays a message indicating that the changes are being undone.
The root cause seems to be limited free space on the EFI system partition. Devices with 10 MB or less of available space are more likely to experience this issue.
What Windows 11 installation failures look like KB5089549
In addition to the rollback message, affected systems may display related entries in C:\Windows\Logs\CBS\CBS.log indicating that there is not enough free space on the EFI system partition. Examples of these registry entries include:
- SpaceCheck: insufficient free space
- BootFiles service failed. Error = 0x70
- SpaceCheck – Used by OEM or third-party files outside of Microsoft boot directories
These messages indicate that the problem is space related and not a broader problem with the installation process.
Microsoft known issue rollback mitigation and workaround for persistent errors
We have implemented mitigation using Known Issue Rollback (KIR) for unmanaged consumer and enterprise devices. In many cases, simply restarting the computer and checking for updates again will allow the update to install normally without any additional steps.
For devices managed by an organization, network administrators must manually deploy a group policy workaround to apply mitigation.
For systems that continue to experience issues after applying KIR mitigation, Microsoft has provided a logging workaround. This reduces the reserved padding that Windows uses within the EFI partition during service.
Editing the registry can be risky and cause system damage if done incorrectly. It is advisable to make a backup of the entire system before making any changes.
To implement the solution, open the Start menu, search for Command Prompt, right-click the top result, and select Run as administrator.
- Type the given command and press Enter. After that, restart the computer.
- Next, open Settings and navigate to Windows Update.
- Click Check for updates. the update
KB5089549 should now download and install successfully after the registry change has been applied.
Permanent fix in development and other Windows 11 2026 update issues
Microsoft has announced that it is working on a permanent fix for the issue, which will be included in a future Windows update. No specific timeline has been provided for when the fix will be released.
This issue is the latest in a series of issues affecting Windows 11 updates in 2026. The April update caused third-party backup software to fail due to a vulnerable driver block, and in the same month, Windows Server 2025 systems experienced crashes and BitLocker recovery messages during update installations.
Devices with older hardware or updated system configurations tend to be more affected by these partition and service issues.
