The May 2026 Windows 11 security update (KB5089549) encountered installation failures due to insufficient free space on the EFI System Partition (ESP), causing error 0x800f0922 and automatic rollback of the update. Devices with 10 MB or less free ESP space were primarily affected, with failures occurring during the reboot phase at approximately 35–36% completion. Microsoft released a fix in the preview cumulative update KB5089573 on May 26, 2026, which addresses this issue and is included in the June Patch Tuesday updates. Users installing KB5089573 or later will not experience this problem. For those who cannot immediately update, Known Issue Rollback and Group Policy workarounds are available to mitigate the issue. This is an update installation issue, not a direct security vulnerability or exploit.

The impact is limited to failed installation of the May 2026 Windows 11 security update on devices with limited EFI System Partition free space, resulting in update rollback and error 0x800f0922. There is no indication of security compromise or exploitation in the wild. The issue may delay deployment of important security updates but does not itself introduce a security risk.

Microsoft has released an official fix in the Windows 11 preview cumulative update KB5089573 (May 26, 2026) and later updates. Installing these updates resolves the installation failure issue. For devices running earlier updates experiencing this problem, Microsoft recommends using the Known Issue Rollback feature or configuring the appropriate Group Policy to mitigate the issue. No other workarounds are necessary if the latest updates are applied.