Windows boot partition runs out of space for Microsoft's May security update

"On affected devices, the installation might proceed through the initial phases but fail during the reboot phase at approximately 35-36% completion. The problem is related to the EFI System Partition (ESP), which is usually where the device boots from. Its minimum size is 200 MB, and the operating system manages it. However, if there is 10 MB or less free space, then the update might fail with a 0x800f0922 error code and the helpful message."

"Microsoft has suggested either a registry edit, which will have administrators rolling their eyes, or a Known Issue Rollback (KIR) to deal with the problem. The company wrote: "The resolution has already propagated automatically to consumer devices and non-managed business devices." As with all security updates, there is important stuff in here that needs to be installed. In earlier coverage, it was described as a "doozy of a Patch Tuesday.""

"The issue affects Windows 11 25H2 and 24H2, and emerged while Microsoft was enjoying a period of no known issues with its operating system products. The admission was made doubly unfortunate by coinciding with a company blog post titled "Improving Windows Quality". Microsoft clearly has more work to do on the quality front, which, frankly, is understandable. Windows is more akin to a supertanker than an agile skiff, and changing direction will take time."

Microsoft reported that the May 2026 security update may fail to install on affected devices with a message indicating changes are being undone. The failure is linked to the EFI System Partition, which typically contains boot files and has a minimum size of 200 MB. If the EFI System Partition has 10 MB or less free space, the update can fail with error code 0x800f0922. Installation may reach early phases but fail during the reboot phase at about 35–36% completion. Microsoft recommended a registry edit or a Known Issue Rollback to resolve the problem. The issue affects Windows 11 25H2 and 24H2 and involves multiple critical CVE fixes.

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