Microsoft says the May 2026 Windows 11 security update KB5089549 can fail to install on certain devices, returning 0x800f0922 and rolling back during the reboot phase at about 35–36%—a problem tied to low free space on the EFI System Partition.
Microsoft has confirmed that the May 2026 Windows 11 security update, KB5089549, is failing to install on some devices and is producing 0x800f0922 errors.
On affected systems, the update can appear to begin normally before backing itself out. Microsoft says installation may run through the initial phases, but fail during the reboot phase at approximately 35–36% completion.
The known issue is linked to insufficient free space on the EFI System Partition (ESP). In particular, Microsoft says it affects devices with limited space on the ESP, especially when a device has 10 MB or less available.
When the rollback happens, users typically see the Windows message “Something didn’t go as planned. Undoing changes.” Microsoft also points to log entries that can help explain the failure, including:
“SpaceCheck: Insufficient free space”
“ServicingBootFiles failed. Error = 0x70”
“SpaceCheck: used by third-party/OEM files outside of Microsoft boot directories”
While Microsoft is working on a fix, it is advising impacted customers to mitigate the problem using Known Issue Rollback, a Windows feature designed to reverse buggy updates pushed through Windows Update.
For enterprise-managed environments. where IT teams control patching behavior. Microsoft says administrators can mitigate the issue manually by installing and configuring a Group Policy.. Microsoft’s guidance is direct: “You will need to install and configure the Group Policy for your version of Windows to resolve this issue.” It also notes that admins must restart affected devices to apply the setting. and that the Group Policy will temporarily disable the change causing the issue.. Microsoft says additional deployment guidance for Known Issue Rollback group policies is available on its support website.
The timeline also matters.. Microsoft released KB5089549 last week as a cumulative update, bundled with dozens of other bug fixes, security patches, and improvements.. That package included a fix for another known issue where some Windows 11 systems could boot into BitLocker recovery after installing the April 2026 Windows security updates.
Earlier in the month. Microsoft addressed other Windows update troubles as well—one involving a Windows Autopatch bug that deployed driver updates restricted by administrative policies on some Autopatch-managed devices across the European Union.. It also confirmed that April 2026 security updates were causing failures in third-party backup applications that use a vulnerable driver.
Taken together. the update failures and rollbacks described here follow the same mechanism: KB5089549 runs until the reboot phase at about 35–36%. then backs out. with Microsoft tying the trigger to “Insufficient free space” on the EFI System Partition and directing admins toward Known Issue Rollback or a Group Policy workaround.
Microsoft Windows 11 KB5089549 May 2026 security update 0x800f0922 EFI System Partition ESP space Known Issue Rollback Group Policy BitLocker recovery Windows Autopatch enterprise IT