Windows 11 KB5089549 Install Failures Complicate Microsoft Defender Security Patches

Microsoft confirmed that the Windows 11 security update KB5089549 can fail to install on systems running versions 24H2 and 25H2 when the EFI System Partition has 10 MB or less of free space. Affected devices typically stop during reboot at about 35–36% completion, return error 0x800f0922, and roll back the update. Microsoft has issued a Known Issue Rollback for consumer and unmanaged business devices, while enterprise administrators must use a Group Policy workaround; for persistent cases, the company also published a registry-based mitigation to reduce reserved EFI servicing padding. The same update also addresses a separate problem that had pushed some Windows 11 devices into BitLocker recovery after earlier 2026 updates.

The installation issue is significant because Microsoft’s May security advisories also included multiple Microsoft Defender vulnerabilities, with CVE-2026-41091 and CVE-2026-45498 added by CISA to the Known Exploited Vulnerabilities catalog, signaling active exploitation risk. Additional Defender flaws tracked as CVE-2026-45584 and related advisories were also published by Microsoft and echoed by national cybersecurity agencies, including Canada’s Cyber Centre and HKCERT, which urged organizations to review the bulletins and apply updates. Microsoft said it is developing a permanent fix for the Windows 11 update failure in a future release.