Windows 11 May 2026 Security Update (KB5089549) fails to install

Windows 11 May 2026 Security Update (KB5089549) was released on May 12, 2026. According to Microsoft, the update was offered on Windows 11 Version 25H2 and 24H2. The update includes the latest security fixes and improvements, along with non-security updates from last month’s optional preview release.

However, when you install this update (KB5089549), some devices might fail to complete installation with a specific error code 0x800f0922. This problem occurs on devices that have limited free space on the EFI System Partition (ESP), especially if it has 10 MB or less available.

Issues associated with KB5089549

There are some known issues with the KB5089549 update released on May 12. Either some of them may be seen by affected users. The issues are acknowledged by Microsoft.

• The update installs successfully during the initial phases.
• The installation fails during the restart phase at approximately 35–36% completion. Windows then rolls back the update.
• You may see the message: Something didn’t go as planned. Undoing changes.
• The installation fails with error code 0x800f0922.

As a result of this issue, you might see log entries similar to the following in C:\Windows\Logs\CBS\CBS.log, indicating insufficient free space on the EFI System Partition:

• SpaceCheck: Insufficient free space
• ServicingBootFiles failed. Error = 0x70
• SpaceCheck: <value> used by third-party/OEM files outside of Microsoft boot directories​​​​​​​

Fixing Windows 11 May 2026 Security Update (KB5089549) fails to install

For consumer PCs

Since KB5089549 is a security update, installing it recommended but there are some workaround you need to employ to avoid the unexpected issue after this update. Microsoft has suggested following workaround to mitigate this issue:

1. Press Windows, or click search icon present on taskbar, type Command Prompt.

2. From search results, select Command Prompt and click Run as administrator.

3. Run the following command:​​​​​​​

reg add “HKLM\SYSTEM\CurrentControlSet\Control\Bfsvc /v EspPaddingPercent /t REG_DWORD /d 0 /f”

4. Close Command Prompt and restart your device.

5. Then you can retry installing the update, it must be installed now.

For enterprise managed devices

As per Microsoft, this issue is mitigated using Known Issue Rollback (KIR). For devices where Windows updates are managed by IT departments, IT administrators can apply the mitigation by installing and configuring a Group Policy in accordance with Known Issue Rollback (KIR).

That’s it!