Earlier this week, Microsoft launched a patch to repair a Safe Boot bypass bug utilized by the BlackLotus bootkit we reported on in March. The unique vulnerability, CVE-2022-21894, was patched in January, however the brand new patch for CVE-2023-24932 addresses one other actively exploited workaround for programs operating Home windows 10 and 11 and Home windows Server variations going again to Home windows Server 2008.
The BlackLotus bootkit is the first-known real-world malware that may bypass Safe Boot protections, permitting for the execution of malicious code earlier than your PC begins loading Home windows and its many safety protections. Safe Boot has been enabled by default for over a decade on most Home windows PCs bought by firms like Dell, Lenovo, HP, Acer, and others. PCs operating Home windows 11 should have it enabled to fulfill the software program’s system necessities.
Microsoft says that the vulnerability may be exploited by an attacker with both bodily entry to a system or administrator rights on a system. It may have an effect on bodily PCs and digital machines with Safe Boot enabled.
We spotlight the brand new repair partly as a result of, not like many high-priority Home windows fixes, the replace will likely be disabled by default for no less than just a few months after it is put in and partly as a result of it would finally render present Home windows boot media unbootable. The repair requires adjustments to the Home windows boot supervisor that may’t be reversed as soon as they have been enabled.
“The Safe Boot function exactly controls the boot media that’s allowed to load when an working system is initiated, and if this repair will not be correctly enabled there’s a potential to trigger disruption and forestall a system from beginning up,” reads one among a number of Microsoft support articles about the update.
Moreover, as soon as the fixes have been enabled, your PC will now not be capable of boot from older bootable media that does not embody the fixes. On the lengthy list of affected media: Home windows set up media like DVDs and USB drives created from Microsoft’s ISO recordsdata; customized Home windows set up photos maintained by IT departments; full system backups; community boot drives together with these utilized by IT departments to troubleshoot machines and deploy new Home windows photos; stripped-down boot drives that use Windows PE; and the restoration media bought with OEM PCs.
Not desirous to abruptly render any customers’ programs unbootable, Microsoft will likely be rolling the replace out in phases over the subsequent few months. The preliminary model of the patch requires substantial user intervention to enable—you first want to put in Might’s safety updates, then use a five-step course of to manually apply and confirm a pair of “revocation recordsdata” that replace your system’s hidden EFI boot partition and your registry. These will make it in order that older, susceptible variations of the bootloader will now not be trusted by PCs.
A second replace will comply with in July that will not allow the patch by default however will make it simpler to allow. A 3rd replace in “first quarter 2024” will allow the repair by default and render older boot media unbootable on all patched Home windows PCs. Microsoft says it’s “on the lookout for alternatives to speed up this schedule,” although it is unclear what that might entail.
Jean-Ian Boutin, ESET’s director of menace analysis, described the severity of BlackLotus and different bootkits to Ars after we initially reported on it:
The last word takeaway is that UEFI bootkit BlackLotus is ready to set up itself on up-to-date programs utilizing the newest Home windows model with safe boot enabled. Despite the fact that the vulnerability is previous, it’s nonetheless potential to leverage it to bypass all safety measures and compromise the booting means of a system, giving the attacker management over the early section of the system startup. It additionally illustrates a pattern the place attackers are specializing in the EFI System Partition (ESP) versus firmware for his or her implants—sacrificing stealthiness for simpler deployment—however permitting the same stage of capabilities.
This repair is not the one latest safety incident to spotlight the difficulties of patching low-level Safe Boot and UEFI vulnerabilities; pc and motherboard maker MSI lately had its signing keys leaked in a ransomware attack, and there isn’t any easy means for the corporate to inform its merchandise to not belief firmware updates signed with the compromised key.