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 techniques working 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 offered by firms like Dell, Lenovo, HP, Acer, and others. PCs working Home windows 11 should have it enabled to satisfy the software program’s system necessities.
Microsoft says that the vulnerability could be exploited by an attacker with both bodily entry to a system or administrator rights on a system. It may well have an effect on bodily PCs and digital machines with Safe Boot enabled.
We spotlight the brand new repair partly as a result of, in contrast to many high-priority Home windows fixes, the replace will probably be disabled by default for not less than a couple of months after it is put in and partly as a result of it can ultimately render present Home windows boot media unbootable. The repair requires modifications 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 shouldn’t be correctly enabled there’s a potential to trigger disruption and stop a system from beginning up,” reads one in all a number of Microsoft assist articles in regards to the replace.
Moreover, as soon as the fixes have been enabled, your PC will not be capable of boot from older bootable media that does not embrace the fixes. On the prolonged checklist of affected media: Home windows set up media like DVDs and USB drives created from Microsoft’s ISO information; 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 Home windows PE; and the restoration media offered with OEM PCs.
Not eager to abruptly render any customers’ techniques unbootable, Microsoft will probably be rolling the replace out in phases over the following few months. The preliminary model of the patch requires substantial person intervention to allow—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 information” 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 not be trusted by PCs.
A second replace will observe 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 “searching for alternatives to speed up this schedule,” although it is unclear what that may 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 final word takeaway is that UEFI bootkit BlackLotus is ready to set up itself on up-to-date techniques utilizing the most recent Home windows model with safe boot enabled. Though the vulnerability is outdated, it’s nonetheless doable to leverage it to bypass all safety measures and compromise the booting technique 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 an identical stage of capabilities.
This repair is not the one current safety incident to spotlight the difficulties of patching low-level Safe Boot and UEFI vulnerabilities; pc and motherboard maker MSI just lately had its signing keys leaked in a ransomware assault, and there is no easy approach for the corporate to inform its merchandise to not belief firmware updates signed with the compromised key.
