Microsoft Windows 11 May Security Update Fails Due to EFI Partition Space Issues

Microsoft's May 2026 security update (KB5089549) for Windows 11 is failing to install on devices with insufficient free space on the EFI System Partition (ESP), particularly those with 10 MB or less. The installation process proceeds initially but fails during reboot at 35-36% completion, resulting in a rollback and the message, 'Something didn't go as planned. Undoing changes.' The issue is confirmed to trigger error code 0x800f0922. Affected users may find log entries indicating insufficient ESP space. Microsoft has provided workarounds, including a registry modification and a Known Issue Rollback (KIR) for enterprise environments. The update includes numerous security patches for critical vulnerabilities. This situation raises concerns about the reliability of the update process and the trust of IT teams in Microsoft's orchestration and validation logic.

Key Points: • The May 2026 Windows 11 security update fails on devices with limited EFI partition space. • Affected systems show error code 0x800f0922 and rollback messages during installation. • Microsoft recommends registry edits and Known Issue Rollback as workarounds.