An anonymous reader quotes a report from Ars Technica: Earlier this week, Microsoft released a patch to fix a Secure Boot bypass bug used by the BlackLotus bootkit we reported on in March. The original vulnerability, CVE-2022-21894, was patched in January, but the new patch for CVE-2023-24932 addresses another actively exploited workaround for systems running Windows 10 and 11 and Windows Server versions going back to Windows Server 2008. The BlackLotus bootkit is the first-known real-world malware that can bypass Secure Boot protections, allowing for the execution of malicious code before your PC begins loading Windows and its many security protections. Secure Boot has been enabled by default for over a decade on most Windows PCs sold by companies like Dell, Lenovo, HP, Acer, and others. PCs running Windows 11 must have it enabled to meet the software's system requirements. Microsoft says that the vulnerability can be exploited by an attacker with either physical access to a system or administrator rights on a system. It can affect physical PCs and virtual machines with Secure Boot enabled. We highlight the new fix partly because, unlike many high-priority Windows fixes, the update will be disabled by default for at least a few months after it's installed and partly because it will eventually render current Windows boot media unbootable. The fix requires changes to the Windows boot manager that can't be reversed once they've been enabled. Additionally, once the fixes have been enabled, your PC will no longer be able to boot from older bootable media that doesn't include the fixes. On the lengthy list of affected media: Windows install media like DVDs and USB drives created from Microsoft's ISO files; custom Windows install images maintained by IT departments; full system backups; network boot drives including those used by IT departments to troubleshoot machines and deploy new Windows images; stripped-down boot drives that use Windows PE; and the recovery media sold with OEM PCs. Not wanting to suddenly render any users' systems unbootable, Microsoft will be rolling the update out in phases over the next few months. The initial version of the patch requires substantial user intervention to enable -- you first need to install May's security updates, then use a five-step process to manually apply and verify a pair of "revocation files" that update your system's hidden EFI boot partition and your registry. These will make it so that older, vulnerable versions of the bootloader will no longer be trusted by PCs. A second update will follow in July that won't enable the patch by default but will make it easier to enable. A third update in "first quarter 2024" will enable the fix by default and render older boot media unbootable on all patched Windows PCs. Microsoft says it is "looking for opportunities to accelerate this schedule," though it's unclear what that would entail.

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