Windows 11 Security Update Installation Failure – KB5089549 (Build 26200.8457)

KB5089549 is a known issue for some Windows 11 devices where the update fails to install and rolls back, typically with error 0x800f0922, especially on systems with low free space on the EFI System Partition (ESP). The issue affects Windows 11, versions 24H2 and 25H2, and is mitigated by a registry-based workaround or by a Known Issue Rollback (KIR).

Use the following steps, in order.

1. Apply the ESP registry workaround (client devices)

This workaround relaxes ESP free-space checks so the update can complete.

1. Open Command Prompt as Administrator.
2. Run this command exactly:

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

3. Restart the device.
4. Run Settings > Windows Update > Check for updates and try installing KB5089549 again.

Editing the registry incorrectly can cause system issues, so ensure the command is entered exactly as shown and that a backup or restore point exists beforehand.

2. Use Known Issue Rollback (KIR)

If the problem persists, or if this is an enterprise-managed device, use the KIR mitigation for KB5089549.

For non‑managed/consumer devices:

• The KIR mitigation is delivered automatically via Windows Update.
• Restart the device once or twice to help the rollback policy apply, then try installing KB5089549 again from Settings > Windows Update.

For enterprise‑managed devices (WSUS/Intune/Group Policy):

1. Download and install the special Group Policy for KB5089549:
   • Download for Windows 11, version 25H2 and Windows 11, version 24H2: KB5089549 260514_06221 Known Issue Rollback (MSI).
2. In Group Policy Management, go to:
   • Computer Configuration > Administrative Templates > <Group Policy name listed in the KIR MSI>.
3. Enable and configure the policy according to the KIR guidance in How to use Group Policy to deploy a Known Issue Rollback.
4. Force a Group Policy update on clients (for example, gpupdate /force) or wait for normal policy refresh.
5. Restart the affected devices and then retry installing KB5089549 from Windows Update.

The KIR policy temporarily disables the change in KB5089549 that is causing the installation failure, allowing the update to install successfully while Microsoft works on a permanent fix.

If, after applying the registry workaround and confirming that KIR has been applied (for managed environments), KB5089549 still fails, capture the exact error code shown in Windows Update (for example, 0x800f0922) and review C:\Windows\Logs\CBS\CBS.log for ESP free-space related entries such as:

• SpaceCheck: Insufficient free space
• ServicingBootFiles failed. Error = 0x70

If those entries are present even after the registry change, involve IT support to review ESP partition usage (especially third‑party/OEM files) before making any partition changes.

References:

• Windows 11, version 24H2 known issues and notifications
• Windows 11, version 25H2 known issues and notifications