September’s Patch Tuesday landed on 9/8. And it brought more than the usual security fixes. KB5124008 and KB5124012 quietly expanded device targeting for Microsoft’s ongoing Secure Boot trust chain. If you haven’t verified your machines yet, now is the time. Secure Boot cleanup is not optional — it is essential maintenance for every managed Windows environment. Indeed, I’d argue that a routine post Patch Tuesday Secure Boot checkup is part of a “new normal” for Windows, with a cleanup to follow if needed.
Why Do a Post Patch Tuesday Secure Boot Check?
Here is the backstory. The old Microsoft UEFI CA certificates that were issued back in 2011, expired in June 2026. Microsoft has been rolling out replacement 2023 certificates through Windows Update for months. September’s updates expanded that rollout further.
KB5124008 and KB5124012 added more “high confidence” device targeting data. That means more PCs are now eligible to receive the new certs automatically. However, some devices still fall through the cracks.
Don’t panic. Devices that haven’t received the new certificates will still boot. Standard Windows updates will still install. But the clock is ticking. A second major deadline arrives in October 2026. You don’t want to be scrambling then.
Why It Matters
Devices that miss the Secure Boot cleanup lose future boot-level security protections. Over time, they become progressively more exposed to boot-level threats. These are the kind that load before Windows even starts. Also, BitLocker and device encryption may break on out-of-synch systems. That means recovery key prompts, startup hangs, and frustrated users calling the help desk.
Running the Garlin Remediation
Garlin is a long-time, high-status (and value) member of the online community for ElevenForum.com. He’s been stewarding a long-running thread (now at 188 pages) entitled “garlin’s PowerShell scripts for updating Secure Boot CA 2023” since January 2025. He’s got scripts to handle certificate synch-ups, with all the related DB and DBX fixes to boot (pun intended). Just remember to visit his GitHub site regularly to download the latest ZIP file with scripts to match (his latest update on 9/8 handles the newest Patch Tuesday updates).
As you can see in the lead-in screenshot, after the update Windows incremented SkuSiPolicy.p7b from version 3.0.0.17 to 3.0.0.18. It also updates the Secure Version Variable (SVN) stored in NVM in firmware as part of Secure Boot’s DBX values. After the OS update, certain operations are need to catch the UEFI up with the OS.
Actual Remediation : SkuSiPolicy.p7b
The SkuSiPolicy.p7b value governs which Windows editions (aka “SKUs” such as Home, Pro, Education, etc.) that Secure Boot regards as trusted and bootable. If the policy in the OS and the policy in a boot structure (whether in EFI, on disk, or on bootable media) don’t match, you get “Secure Boot Violation” when you try to boot and nothing more. Not good!
No worries. Garlin’s got a fix for that. If you run his latest Update UEFI script with the right argument it will fix it for you (reboot required). Here’s the syntax:
Update_UEFI-CA2023.ps1 -SkuSiPolicy
If you’re running this in an admin PowerShell session, prepend “.\” (period-backslash) to get it to run. Tip: if you unblock the ZIP file after downloading it from GitHub, the archive’s content will also be unblocked. Otherwise, you’ll end up unblocking them piecemeal. I speak from direct experience on this…
Actual Remediation: SVN
The Secure Version Number (acronym: SVN) is a monotonically increasing integer value also stored in the UEFI DBX value. It provides anti-rollback enforcement. When a bootloader or boot manager tries to loan, UEFI checks its built-in SVN against the minimum SVN stored in firmware. If the boot agent SVN is lower than what’s in UEFI, UEFI won’t load it. Here again, it’s necessary for what’s in the OS and what in the bootloader to agree. After an update (like Patch Tuesday) remediation may be needed.
Here’s what that looks like in PowerShell (admin):
manage-bde -Protectors -Disable C: -RebootCount 1
reg add HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Secureboot /v AvailableUpdates /t REG_DWORD /d 0x200 /f
powershell Start-ScheduledTask -TaskName "\Microsoft\Windows\PI\Secure-Boot-Update"
The first line turns off BitLocker for the next boot to avoid key lookup and entry. It’s only needed for PCs whose C: drive is BitLocker protected. The next line adds a registry key to define and schedule a Secure Boot update task to update the SVN. The third line calls powershell to run that scheduled task immediately. All this stuff shows up in the output of the Garlin check script if you run it properly, so you can copy it from there, right inside PowerShell.
Here’s that syntax:
check_uEFI-CA2023.ps1 -verbose -audit
Don’t forget to prepend the “.\” (period backslash) to run it in PS.
Also: Boot Media Needs Catchup, Too
Here is a step that many admins overlook. Your Windows installation USB drives and WinPE recovery media also need attention. For sure, any media created before January 2025 won’t include the new 2023 Secure Boot certificates. I’ve gotten in the habit of rebuilding boot media each time that SkuSiPolicy.p7b or the SVN increments myself.
What happens if you don’t build new boot media? They may fail to launch on a fully updated machine. Rebuild everything from the latest Windows ADK, MCT (Media Creation Tool), or a current Windows ISO. Then test the rebuilt media on at least one device before you rely on it to get something done.
Run through this quick checklist before you close this task out:
- ☑ Rebuild WinPE USB from the latest ADK
- ☑ Rebuild Windows installation USB from a current ISO
- ☑ Update MDT and WDS boot images if applicable
- ☑ Test rebuilt media on a pilot device before wide deployment
- ☑ Document any devices that cannot update (unsupported hardware) as formal exceptions
This is a new and interesting wrinkle on dealing with Windows Updates, especially around the Patch Tuesday milestone. Here in Windows-World such wrinkles accumulate. Don’t let them put your PCs and boot media in peril. Do the necessary, please!
