Earlier this week, Microsoft launched a patch to repair a Secure Boot bypass bug utilized by the BlackLotus bootkit we reported on in March. The authentic 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 Windows 10 and 11 and Windows Server variations going again to Windows Server 2008.
The BlackLotus bootkit is the first-known real-world malware that may bypass Secure Boot protections, permitting for the execution of malicious code earlier than your PC begins loading Windows and its many safety protections. Secure Boot has been enabled by default for over a decade on most Windows PCs offered by firms like Dell, Lenovo, HP, Acer, and others. PCs working Windows 11 will need to 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 can have an effect on bodily PCs and digital machines with Secure Boot enabled.
We spotlight the brand new repair partly as a result of, in contrast to many high-priority Windows fixes, the replace shall be disabled by default for no less than a couple of months after it is put in and partly as a result of it’s going to finally render present Windows boot media unbootable. The repair requires modifications to the Windows boot supervisor that may’t be reversed as soon as they have been enabled.
“The Secure Boot characteristic 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 stop a system from beginning up,” reads certainly one of a number of Microsoft help articles in regards to the replace.
Additionally, as soon as the fixes have been enabled, your PC will not be capable of boot from older bootable media that does not embody the fixes. On the prolonged checklist of affected media: Windows set up media like DVDs and USB drives created from Microsoft’s ISO recordsdata; customized 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 Windows photos; stripped-down boot drives that use Windows PE; and the restoration media offered with OEM PCs.
Not desirous to out of the blue render any customers’ techniques unbootable, Microsoft shall 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 May’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 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 Windows PCs. Microsoft says it’s “in search of alternatives to speed up this schedule,” although it is unclear what that might entail.
Jean-Ian Boutin, ESET’s director of risk analysis, described the severity of BlackLotus and different bootkits to Ars once we initially reported on it:
The final takeaway is that UEFI bootkit BlackLotus is ready to set up itself on up-to-date techniques utilizing the newest Windows model with safe boot enabled. Even although the vulnerability is previous, it’s nonetheless potential to leverage it to bypass all safety measures and compromise the booting technique of a system, giving the attacker management over the early part of the system startup. It additionally illustrates a development 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 degree of capabilities.
This repair is not the one latest safety incident to spotlight the difficulties of patching low-level Secure Boot and UEFI vulnerabilities; laptop and motherboard maker MSI just lately had its signing keys leaked in a ransomware assault, and there isn’t any easy approach for the corporate to inform its merchandise to not belief firmware updates signed with the compromised key.