ESET researchers have found a vulnerability that permits bypassing UEFI Safe Boot, affecting the vast majority of UEFI-based programs. This vulnerability, assigned CVE-2024-7344, was present in a UEFI utility 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 (equivalent to Bootkitty or BlackLotus) even on programs with UEFI Safe Boot enabled, whatever the put in working system.
The affected UEFI utility 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 Know-how Inc., Pc Schooling System Inc., and Sign Pc GmbH. Following is the record of weak 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 prompted by way of a customized PE loader as an alternative of utilizing the usual and safe UEFI capabilities LoadImage and StartImage. Because of this, the appliance 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 Heart (CERT/CC) in June 2024, which efficiently contacted the affected distributors. The problem has now been mounted of their merchandise and the previous, weak binaries have been revoked by Microsoft within the January 14th, 2025 Patch Tuesday replace.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 programs.
- Exploitation of this vulnerability permits execution of untrusted code throughout system boot, enabling deployment of malicious UEFI bootkits.
- All UEFI programs with Microsoft third-party UEFI signing enabled are affected (Home windows 11 Secured-core PCs ought to have this feature disabled by default).
- The problem was mounted by affected distributors and previous, weak binaries have 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 supplied preliminary patch for evaluate.
- 2024-08-20: ESET confirmed the reported concern was addressed accurately, however found one other newly launched concern with the identical root trigger.
- 2024-08-28: Distributors supplied 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 weak UEFI functions by Microsoft.
- 2025-01-16: ESET blogpost printed.
UEFI Safe Boot in the true world
Earlier than leaping in to describing the vulnerability, let’s take a look at how UEFI Safe Boot verification works on actual gadgets, and who’s accountable for managing the UEFI Safe Boot databases on them.
The fundamental logic is sort of easy and is depicted in Determine 1. When UEFI Boot Supervisor proceeds to load a boot utility, equivalent to Home windows Boot Supervisor, shim, GRUB2, or related, amongst different checks, it verifies the boot utility binary in opposition to two Safe Boot databases:
- db – record of allowed certificates or PE Authenticode hashes, trusted by the platform firmware.
- dbx – record of forbidden certificates or PE Authenticode hashes.
The situations are that the verified picture needs to be trusted by the db and, on the identical time, the file’s hash or its certificates should not be listed within the dbx database. Primarily based 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 strategy of main working programs on newly bought UEFI gadgets (by default and with out person interplay), most gadgets include a set of particular UEFI certificates enrolled of their db database. Whereas these certificates can range primarily based on the OEM and the particular machine’s necessities and goal, on most common gadgets (equivalent to laptops, desktops, servers…), Microsoft asks OEMs to incorporate Microsoft’s personal certificates. That’s why Microsoft performs an essential function in securing most of such UEFI-based gadgets, 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 gadgets include Microsoft’s UEFI certificates enrolled. The next are two particular certificates which are often current among the many trusted ones on such gadgets:
- Microsoft Home windows Manufacturing PCA 2011
- Microsoft Company UEFI CA 2011
Observe that the Microsoft Home windows Manufacturing PCA 2011 certificates needs to be revoked and changed with the Home windows UEFI CA 2023 certificates by Microsoft quickly (extra data), as a response to the weak Home windows bootloaders associated to the notorious BlackLotus bootkit. New or up to date Home windows gadgets 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 functions; nonetheless, it must also get replaced sooner or later with a brand new certificates known as Microsoft UEFI CA 2023. For anybody all for 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 functions, the latter is utilized by Microsoft to signal UEFI boot software program developed by third events, which incorporates Linux shims, numerous specialised restoration, backup, disk encryption, or upkeep software program, and so forth…
Because of this anybody all for 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 Heart dashboard), and if the binaries go Microsoft’s inside evaluate, Microsoft indicators them with its third-party UEFI certificates and thus the recordsdata turn out to be appropriate with the vast majority of UEFI programs, which belief Microsoft’s third-party certificates (on Home windows 11 Secured-core PCs, Microsoft’s third-party UEFI certificates shouldn’t be thought of as trusted by default).
From the Microsoft UEFI signing necessities accessible on-line, it’s unclear what the interior evaluate course of consists of, although it definitely evokes some deeper evaluation as an alternative of simply strolling by way of the listed necessities. Whereas we imagine that the handbook evaluate course of is being improved over time with each new vulnerability found, larger transparency in what is definitely being signed and in what checks this handbook evaluate course of consists of might enhance the probabilities that such clearly weak binaries because the one described on this report are found and stuck sooner.
CVE-2024-7344
After 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 utility named reloader.efi. Following are the PE Authenticode hashes of the weak reloader.efi utility:
- 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 accommodates 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 simple to guess the important thing primarily based on the frequency of 0xB3 bytes, comparable to the plethora of 0x00 bytes current in common PE/COFF headers. Decrypting cloak.dat by utilizing an XOR operation with the important thing 0xB3 reveals that it certainly accommodates a UEFI utility – furthermore, an unsigned one.
We rapidly came upon that the extracted binary isn’t malicious, however we questioned: is that this binary by some means utilized by SysReturn’s bootloader throughout system begin? If that’s the case, does it take UEFI Safe Boot into consideration and refuse to load this unsigned binary if enabled? After trying deeper into reloader.efi, we discovered code accountable for loading cloak.dat file into reminiscence and decrypting the embedded picture. As proven in Determine 3, the operate tries to load the file from one of many following places 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 might nonetheless go the buffer containing the decrypted PE picture to the UEFI’s LoadImage operate as an argument, which might make sure 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 weak bootloader calls its personal operate depicted in Determine 4, accountable 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 under.
Exploitation of this vulnerability is just not restricted to programs with the affected restoration software program put in, as attackers can deliver their very own copy of the weak reloader.efi binary to any UEFI system with the Microsoft third-party UEFI certificates enrolled. Additionally, elevated privileges are required to deploy the weak and malicious recordsdata to the EFI system partition (native administrator on Home windows; root on Linux). To use the vulnerability, an attacker would wish to:
- Change a default OS bootloader binary on the EFI system partition (ESP) with the weak reloader.efi.
- Copy a specifically crafted cloak.dat file, containing a malicious UEFI utility, to one of many paths on the ESP supported by the weak bootloader.
- Reboot the system.
After we confirmed the vulnerability by making a working proof of idea, we observed that the weak reloader.efi utility was used not solely by Howyar’s SysReturn software program, but in addition by a number of further restoration software program merchandise. An exhaustive record of affected software program packages may be discovered in the beginning of this blogpost. As a couple of 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, now we have not detected any real-world exploitation makes an attempt in our telemetry information.
Safety and detection
The vulnerability may be mitigated by making use of the newest UEFI revocations from Microsoft. Home windows programs needs to be up to date routinely. Microsoft’s advisory for the CVE-2024-7344 vulnerability may be discovered right here. Use the next PowerShell instructions (run with elevated permissions) to test whether or not you’re affected by the vulnerability and if the required revocations have been put in in your system:
# UEFI programs; 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 programs; returns True for those who’re protected (the weak driver is revoked in your system)
[BitConverter]::ToString((Get-SecureBootUEFI dbx).bytes) -replace ‘-‘ -match ‘cdb7c90d3ab8833d5324f5d8516d41fa990b9ca721fe643fffaef9057d9f9e48’
# 32-bit UEFI programs; returns True for those who’re protected (the weak driver is revoked in your system)
[BitConverter]::ToString((Get-SecureBootUEFI dbx).bytes) -replace ‘-‘ -match ‘e9e4b5a51f6a5575b9f5bfab1852b0cb2795c66ff4b28135097cba671a5491b9’
For Linux programs, updates needs to be accessible by way of the Linux Vendor Firmware Service. Use the next instructions to test whether or not the required revocations are put in in your system:
dbxtool –list | grep ‘cdb7c90d3ab8833d5324f5d8516d41fa990b9ca721fe643fffaef9057d9f9e48’
dbxtool –list | grep ‘e9e4b5a51f6a5575b9f5bfab1852b0cb2795c66ff4b28135097cba671a5491b9’
Whereas UEFI revocations successfully shield your system in opposition to CVE-2024-7344, there are different kind of efficient methods of defending in opposition to (or at the very least detecting) exploitation of unknown weak signed UEFI bootloaders and deployment of UEFI bootkits, together with:
- Managed entry to recordsdata situated on the EFI system partition. In most UEFI bootkit set up situations, an attacker wants to change the contents of the EFI system partition with a view to set up a UEFI bootkit or to use a vulnerability in a signed UEFI bootloader on the focused system. Most safety merchandise enable creation of customized user-defined file entry guidelines that enable blocking entry to particular recordsdata 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 in opposition to UEFI bootkits or, at the very least, to cut back the assault floor or enable sooner revocations of weak UEFI functions to system house owners if official revocation updates take an extended time. Whereas efficient, it typically requires skilled directors (improper Safe Boot configurations could make programs quickly unbootable) and it may be troublesome to handle at scale.
- Distant attestation with TPM, the place measurements of UEFI boot elements and configuration may be validated in opposition to their recognized 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 weak binaries inside an inexpensive time window reveals that even such a vital function as UEFI Safe Boot shouldn’t be thought of an impenetrable barrier.
Nonetheless, what considerations us essentially the most within the case of the vulnerability reported on this blogpost is just not 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 weak UEFI utility (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 the usage of such unsafe methods is amongst third-party UEFI software program distributors, and what number of different such obscure, however signed, bootloaders there may be on the market. We reached out to Microsoft in regards to the state of affairs, hoping it might deliver extra transparency into what third-party UEFI functions they signal, in order that anybody can rapidly uncover and report such clearly unsafe UEFI functions 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 imagine that Microsoft’s deliberate rollout of latest UEFI certificates offers an awesome 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 provides non-public APT intelligence experiences and information feeds. For any inquiries about this service, go to the ESET Risk Intelligence web page.
IoCs
Because the weak loaders are a part of authentic software program packages which are probably current on hundreds of programs which have by no means been compromised by way of these loaders, we’re not offering indicators of compromise to keep away from large misidentification. As a substitute, defenders ought to observe the recommendation within the Safety and detection part.
