ESET researchers have found a vulnerability that permits bypassing UEFI Safe Boot, affecting the vast majority of UEFI-based methods. This vulnerability, assigned CVE-2024-7344, was present in a UEFI software signed by Microsoft’s Microsoft Company UEFI CA 2011 third-party UEFI certificates. Exploitation of this vulnerability results in the execution of untrusted code throughout system boot, enabling potential attackers to simply deploy malicious UEFI bootkits (corresponding to Bootkitty or BlackLotus) even on methods with UEFI Safe Boot enabled, whatever the put in working system.
The affected UEFI software is a part of a number of real-time system restoration software program suites developed by Howyar Applied sciences Inc., Greenware Applied sciences, Radix Applied sciences Ltd., SANFONG Inc., Wasay Software program Expertise Inc., Laptop Schooling System Inc., and Sign Laptop GmbH. Following is the checklist of susceptible software program merchandise:
- Howyar SysReturn earlier than model 10.2.023_20240919
- Greenware GreenGuard earlier than model 10.2.023-20240927
- Radix SmartRecovery earlier than model 11.2.023-20240927
- Sanfong EZ-back System earlier than model 10.3.024-20241127
- WASAY eRecoveryRX earlier than model 8.4.022-20241127
- CES NeoImpact earlier than model 10.1.024-20241127
- SignalComputer HDD King earlier than model 10.3.021-20241127
The vulnerability is brought about by means of a customized PE loader as an alternative of utilizing the usual and safe UEFI capabilities LoadImage and StartImage. Because of this, the applying permits the loading of any UEFI binary – even an unsigned one – from a specifically crafted file named cloak.dat, throughout system begin, whatever the UEFI Safe Boot state.
We reported our findings to the CERT Coordination Middle (CERT/CC) in June 2024, which efficiently contacted the affected distributors. The difficulty has now been fastened of their merchandise and the outdated, susceptible binaries had been revoked by Microsoft within the January 14th, 2025 Patch Tuesday replace.
Key factors of this blogpost:
- ESET researchers found a brand new vulnerability, CVE-2024-7344, that permits bypassing UEFI Safe Boot on the vast majority of UEFI-based methods.
- Exploitation of this vulnerability permits execution of untrusted code throughout system boot, enabling deployment of malicious UEFI bootkits.
- All UEFI methods with Microsoft third-party UEFI signing enabled are affected (Home windows 11 Secured-core PCs ought to have this selection disabled by default).
- The difficulty was fastened by affected distributors and outdated, susceptible binaries had been revoked by Microsoft within the January 14th, 2025 Patch Tuesday replace.
Following is the coordinated disclosure timeline. We’d wish to thank CERT/CC for its assist in coordinating the vulnerability disclosure course of, and the affected distributors for easy and clear communication and cooperation in the course of the vulnerability disclosure and remediation course of.
Coordinated disclosure timeline:
- 2024-07-08: ESET discovered the vulnerability.
- 2024-07-09: ESET reported the vulnerability to CERT/CC.
- 2024-07-23: CERT/CC agreed to assist us coordinate the vulnerability disclosure course of – public disclosure date was set to 2024-10-21.
- 2024-08-05: CERT/CC efficiently reached out to the affected distributors.
- 2024-08-20: Distributors offered preliminary patch for evaluate.
- 2024-08-20: ESET confirmed the reported situation was addressed appropriately, however found one other newly launched situation with the identical root trigger.
- 2024-08-28: Distributors offered second patch for evaluate.
- 2024-09-23: We agreed with Microsoft on the brand new public disclosure date of 2025-01-14.
- 2025-01-14: Revocation of affected susceptible UEFI purposes by Microsoft.
- 2025-01-16: ESET blogpost printed.
UEFI Safe Boot in the actual world
Earlier than leaping in to describing the vulnerability, let’s take a look at how UEFI Safe Boot verification works on actual units, and who’s chargeable for managing the UEFI Safe Boot databases on them.
The essential logic is kind of easy and is depicted in Determine 1. When UEFI Boot Supervisor proceeds to load a boot software, corresponding to Home windows Boot Supervisor, shim, GRUB2, or related, amongst different checks, it verifies the boot software binary towards two Safe Boot databases:
- db – checklist of allowed certificates or PE Authenticode hashes, trusted by the platform firmware.
- dbx – checklist of forbidden certificates or PE Authenticode hashes.
The circumstances are that the verified picture must be trusted by the db and, on the similar time, the file’s hash or its certificates should not be listed within the dbx database. Based mostly on the verification outcomes, the UEFI boot supervisor both causes a safety violation or executes the verified picture.
To make sure that UEFI Safe Boot can safe the boot means of main working methods on newly bought UEFI units (by default and with out person interplay), most units include a set of particular UEFI certificates enrolled of their db database. Whereas these certificates can fluctuate primarily based on the OEM and the particular gadget’s necessities and objective, on most common units (corresponding to laptops, desktops, servers…), Microsoft asks OEMs to incorporate Microsoft’s personal certificates. That’s why Microsoft performs an essential position in securing most of such UEFI-based units, as with Microsoft’s keys enrolled in db, Microsoft can handle what’s allowed, and what’s not allowed, to be executed throughout boot.
Microsoft UEFI certificates
As defined above, many UEFI units include Microsoft’s UEFI certificates enrolled. The next are two particular certificates which can be normally current among the many trusted ones on such units:
- Microsoft Home windows Manufacturing PCA 2011
- Microsoft Company UEFI CA 2011
Notice that the Microsoft Home windows Manufacturing PCA 2011 certificates must be revoked and changed with the Home windows UEFI CA 2023 certificates by Microsoft quickly (extra information), as a response to the susceptible Home windows bootloaders associated to the notorious BlackLotus bootkit. New or up to date Home windows units will already belief this new certificates. Within the case of the Microsoft Company UEFI CA 2011 certificates, it nonetheless appears to be used for signing new UEFI purposes; nonetheless, it also needs to get replaced sooner or later with a brand new certificates referred to as Microsoft UEFI CA 2023. For anybody excited by Microsoft’s UEFI certificates rolling plan, take a look on the Evolving the Safe Boot Ecosystem slides offered on the UEFI Fall 2023 Builders Convention & Plugfest.
Whereas the previous certificates (the PCA one) is utilized by Microsoft to signal its personal UEFI boot purposes, the latter is utilized by Microsoft to signal UEFI boot software program developed by third events, which incorporates Linux shims, varied specialised restoration, backup, disk encryption, or upkeep software program, and so forth…
Which means anybody excited by having their boot-time software program UEFI Safe Boot-compatible by default can ask Microsoft to signal their binaries (by way of the Home windows {Hardware} Dev Middle dashboard), and if the binaries go Microsoft’s inside evaluate, Microsoft indicators them with its third-party UEFI certificates and thus the information turn out to be suitable with the vast majority of UEFI methods, which belief Microsoft’s third-party certificates (on Home windows 11 Secured-core PCs, Microsoft’s third-party UEFI certificates shouldn’t be thought-about as trusted by default).
From the Microsoft UEFI signing necessities accessible on-line, it’s unclear what the inner evaluate course of consists of, despite the fact that it actually evokes some deeper evaluation as an alternative of simply strolling by way of the listed necessities. Whereas we consider that the guide evaluate course of is being improved over time with each new vulnerability found, better transparency in what is definitely being signed and in what checks this guide evaluate course of consists of may enhance the possibilities that such clearly susceptible binaries because the one described on this report are found and stuck sooner.
CVE-2024-7344
Once we encountered Howyar’s SysReturn software program bundle final 12 months, the very first thing that instantly caught our consideration was the presence of a file named cloak.dat deployed together with a Microsoft-signed UEFI software named reloader.efi. Following are the PE Authenticode hashes of the susceptible reloader.efi software:
- cdb7c90d3ab8833d5324f5d8516d41fa990b9ca721fe643fffaef9057d9f9e48 (64-bit model)
- e9e4b5a51f6a5575b9f5bfab1852b0cb2795c66ff4b28135097cba671a5491b9 (32-bit model)
On this evaluation, we use the 64-bit model of reloader.efi. As proven in Determine 2, the cloak.dat file comprises a header-like information construction beginning with the magic string ALRM. This header is adopted by unknown information visually resembling the construction of a PE/COFF file header, encrypted utilizing a easy XOR cipher. It’s straightforward to guess the important thing primarily based on the frequency of 0xB3 bytes, akin to the plethora of 0x00 bytes current in common PE/COFF headers. Decrypting cloak.dat through the use of an XOR operation with the important thing 0xB3 reveals that it certainly comprises a UEFI software – furthermore, an unsigned one.
We shortly discovered that the extracted binary isn’t malicious, however we puzzled: is that this binary in some way utilized by SysReturn’s bootloader throughout system begin? In that case, does it take UEFI Safe Boot into consideration and refuse to load this unsigned binary if enabled? After wanting deeper into reloader.efi, we discovered code chargeable for loading cloak.dat file into reminiscence and decrypting the embedded picture. As proven in Determine 3, the perform tries to load the file from one of many following areas on the EFI system partition:
- EFIMicrosoftbootcloak64.dat
- EFIbootcloak64.dat
- EFIMicrosoftbootcloak.dat
- EFIbootcloak.dat
To this point, there wouldn’t be something mistaken with that – the bootloader may nonetheless go the buffer containing the decrypted PE picture to the UEFI’s LoadImage perform as an argument, which might be certain that the picture meets the machine’s UEFI Safe Boot coverage by the verification course of described in Determine 1. Sadly, this isn’t the case. After decryption of a PE picture from the cloak.dat file, the susceptible bootloader calls its personal perform depicted in Determine 4, chargeable for manually loading and executing the picture with none Safe Boot-related integrity checks.
A proof of idea demonstrating exploitation of the vulnerability on a system with UEFI Safe Boot enabled is proven within the video beneath.
Exploitation of this vulnerability isn’t restricted to methods with the affected restoration software program put in, as attackers can carry their very own copy of the susceptible reloader.efi binary to any UEFI system with the Microsoft third-party UEFI certificates enrolled. Additionally, elevated privileges are required to deploy the susceptible and malicious information to the EFI system partition (native administrator on Home windows; root on Linux). To use the vulnerability, an attacker would wish to:
- Exchange a default OS bootloader binary on the EFI system partition (ESP) with the susceptible reloader.efi.
- Copy a specifically crafted cloak.dat file, containing a malicious UEFI software, to one of many paths on the ESP supported by the susceptible bootloader.
- Reboot the system.
After we confirmed the vulnerability by making a working proof of idea, we observed that the susceptible reloader.efi software was used not solely by Howyar’s SysReturn software program, but additionally by a number of extra restoration software program merchandise. An exhaustive checklist of affected software program packages might be discovered at first of this blogpost. As multiple product developed by totally different distributors gave the impression to be affected, we contacted CERT/CC, who helped us attain out to the affected events and coordinate the vulnerability disclosure course of.
To this point, we have now not detected any real-world exploitation makes an attempt in our telemetry information.
Safety and detection
The vulnerability might be mitigated by making use of the most recent UEFI revocations from Microsoft. Home windows methods must be up to date mechanically. Microsoft’s advisory for the CVE-2024-7344 vulnerability might be discovered right here. Use the next PowerShell instructions (run with elevated permissions) to verify whether or not you’re affected by the vulnerability and if the mandatory revocations had been put in in your system:
# UEFI methods; returns True in case your system is affected by the CVE-2024-7344
[System.Text.Encoding]::ASCII.GetString((Get-SecureBootUEFI db).bytes) -match ‘Microsoft Company UEFI CA 2011’
# 64-bit UEFI methods; returns True if you happen to’re protected (the susceptible driver is revoked in your system)
[BitConverter]::ToString((Get-SecureBootUEFI dbx).bytes) -replace ‘-‘ -match ‘cdb7c90d3ab8833d5324f5d8516d41fa990b9ca721fe643fffaef9057d9f9e48’
# 32-bit UEFI methods; returns True if you happen to’re protected (the susceptible driver is revoked in your system)
[BitConverter]::ToString((Get-SecureBootUEFI dbx).bytes) -replace ‘-‘ -match ‘e9e4b5a51f6a5575b9f5bfab1852b0cb2795c66ff4b28135097cba671a5491b9’
For Linux methods, updates must be accessible by way of the Linux Vendor Firmware Service. Use the next instructions to verify whether or not the mandatory revocations are put in in your system:
dbxtool –list | grep ‘cdb7c90d3ab8833d5324f5d8516d41fa990b9ca721fe643fffaef9057d9f9e48’
dbxtool –list | grep ‘e9e4b5a51f6a5575b9f5bfab1852b0cb2795c66ff4b28135097cba671a5491b9’
Whereas UEFI revocations successfully shield your system towards CVE-2024-7344, there are different roughly efficient methods of defending towards (or at the least detecting) exploitation of unknown susceptible signed UEFI bootloaders and deployment of UEFI bootkits, together with:
- Managed entry to information situated on the EFI system partition. In most UEFI bootkit set up eventualities, an attacker wants to change the contents of the EFI system partition so as to set up a UEFI bootkit or to use a vulnerability in a signed UEFI bootloader on the focused system. Most safety merchandise permit creation of customized user-defined file entry guidelines that permit blocking entry to particular information or directories on the system (e.g., right here and right here).
- UEFI Safe Boot customization. As detailed within the NSA’s UEFI Safe Boot Customization report, Safe Boot customization can be utilized to successfully shield towards UEFI bootkits or, at the least, to cut back the assault floor or permit quicker revocations of susceptible UEFI purposes to system house owners if official revocation updates take an extended time. Whereas efficient, it usually requires skilled directors (improper Safe Boot configurations could make methods quickly unbootable) and it may be troublesome to handle at scale.
- Distant attestation with TPM, the place measurements of UEFI boot elements and configuration might be validated towards their identified good values by a trusted distant server, and thus used to detect unauthorized boot modifications.
Conclusion
The variety of UEFI vulnerabilities found in recent times and the failures in patching them or revoking susceptible binaries inside an affordable time window reveals that even such a necessary function as UEFI Safe Boot shouldn’t be thought-about an impenetrable barrier.
Nevertheless, what considerations us probably the most within the case of the vulnerability reported on this blogpost isn’t the time it took to repair and revoke the binary, which was fairly good in comparison with related instances, however the truth that this isn’t the primary time that such an clearly unsafe signed UEFI binary has been found. In actuality, a really related Microsoft-signed susceptible UEFI software (CVE-2022-34302), implementing its personal unsafe PE loader, was found about two years in the past by Eclypsium in One Bootloader to Load Them All.
This raises questions of how widespread using such unsafe strategies is amongst third-party UEFI software program distributors, and what number of different such obscure, however signed, bootloaders there is likely to be on the market. We reached out to Microsoft concerning the state of affairs, hoping it may carry extra transparency into what third-party UEFI purposes they signal, in order that anybody can shortly uncover and report such clearly unsafe UEFI purposes in the event that they mistakenly go (or handed a very long time in the past) Microsoft’s UEFI third-party code-signing evaluate. We consider that Microsoft’s deliberate rollout of latest UEFI certificates offers an important alternative to make this occur, pushing UEFI third-party signing transparency and UEFI safety one step ahead.
For any inquiries about our analysis printed on WeLiveSecurity, please contact us at threatintel@eset.com.ESET Analysis presents personal APT intelligence experiences and information feeds. For any inquiries about this service, go to the ESET Menace Intelligence web page.
IoCs
Because the susceptible loaders are a part of authentic software program packages which can be probably current on 1000’s of methods which have by no means been compromised through these loaders, we aren’t offering indicators of compromise to keep away from large misidentification. As an alternative, defenders ought to observe the recommendation within the Safety and detection part.
