Below the cloak of UEFI Safe Boot: Introducing CVE-2024-7344

ESET researchers have found a vulnerability that permits bypassing UEFI Safe Boot, affecting the vast majority of UEFI-based techniques. 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 (reminiscent of Bootkitty or BlackLotus) even on techniques 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 Know-how Inc., Laptop Training System Inc., and Sign Laptop 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 triggered by means of a customized PE loader as an alternative of utilizing the usual and safe UEFI capabilities LoadImage and StartImage. Consequently, 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 Middle (CERT/CC) in June 2024, which efficiently contacted the affected distributors. The difficulty has now been fastened of their merchandise and the outdated, weak binaries had been revoked by Microsoft within the January 14^th, 2025 Patch Tuesday replace.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 techniques.
• Exploitation of this vulnerability permits execution of untrusted code throughout system boot, enabling deployment of malicious UEFI bootkits.
• All UEFI techniques with Microsoft third-party UEFI signing enabled are affected (Home windows 11 Secured-core PCs ought to have this feature disabled by default).
• The difficulty was fastened by affected distributors and outdated, weak binaries had been revoked by Microsoft within the January 14^th, 2025 Patch Tuesday replace.

Following is the coordinated disclosure timeline. We’d prefer 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 throughout 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 concern was addressed accurately, however found one other newly launched concern 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 weak UEFI functions by Microsoft.
• 2025-01-16: ESET blogpost revealed.

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 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 software, reminiscent of Home windows Boot Supervisor, shim, GRUB2, or comparable, amongst different checks, it verifies the boot software 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 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 strategy of main working techniques 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 range primarily based on the OEM and the particular machine’s necessities and objective, on most common units (reminiscent of laptops, desktops, servers…), Microsoft asks OEMs to incorporate Microsoft’s personal certificates. That’s why Microsoft performs an necessary function 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 often current among the many trusted ones on such units:

• Microsoft Home windows Manufacturing PCA 2011
• Microsoft Company UEFI CA 2011

Be aware 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 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 functions; nonetheless, it also needs to get replaced sooner or later with a brand new certificates referred to as Microsoft UEFI CA 2023. For anybody taken with Microsoft’s UEFI certificates rolling plan, take a look on the Evolving the Safe Boot Ecosystem slides introduced 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, varied specialised restoration, backup, disk encryption, or upkeep software program, and so forth…

Because of this anybody taken with having their boot-time software program UEFI Safe Boot-compatible by default can ask Microsoft to signal their binaries (by 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 into appropriate with the vast majority of UEFI techniques, 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 actually evokes some deeper evaluation as an alternative of simply strolling by the listed necessities. Whereas we consider that the guide evaluate course of is being improved over time with each new vulnerability found, higher transparency in what is definitely being signed and in what checks this guide 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

Once we encountered Howyar’s SysReturn software program package deal 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 weak 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 incorporates 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, akin 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 incorporates a UEFI software – furthermore, an unsigned one.

We shortly came upon that the extracted binary isn’t malicious, however we questioned: is that this binary in some way 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 wanting 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 areas on the EFI system partition:

• EFIMicrosoftbootcloak64.dat
• EFIbootcloak64.dat
• EFIMicrosoftbootcloak.dat
• EFIbootcloak.dat

Thus far, there wouldn’t be something flawed 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 isn’t restricted to techniques 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 information to the EFI system partition (native administrator on Home windows; root on Linux). To take advantage of the vulnerability, an attacker would wish to:

1. Change a default OS bootloader binary on the EFI system partition (ESP) with the weak reloader.efi.
2. Copy a specifically crafted cloak.dat file, containing a malicious UEFI software, to one of many paths on the ESP supported by the weak bootloader.
3. Reboot the system.

After we confirmed the vulnerability by making a working proof of idea, we observed that the weak reloader.efi software was used not solely by Howyar’s SysReturn software program, but in addition by a number of extra restoration software program merchandise. An exhaustive record of affected software program packages could be discovered at first of this blogpost. As a couple of product developed by totally different distributors appeared to be affected, we contacted CERT/CC, who helped us attain out to the affected events and coordinate the vulnerability disclosure course of.

Thus far, we have now not detected any real-world exploitation makes an attempt in our telemetry information.

Safety and detection

The vulnerability could be mitigated by making use of the newest UEFI revocations from Microsoft. Home windows techniques needs to be up to date robotically. Microsoft’s advisory for the CVE-2024-7344 vulnerability could 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 required revocations had been put in in your system:

# UEFI techniques; 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 techniques; returns True in the event you’re protected (the weak driver is revoked in your system)

[BitConverter]::ToString((Get-SecureBootUEFI dbx).bytes) -replace ‘-‘ -match ‘cdb7c90d3ab8833d5324f5d8516d41fa990b9ca721fe643fffaef9057d9f9e48’

# 32-bit UEFI techniques; returns True in the event you’re protected (the weak driver is revoked in your system)

[BitConverter]::ToString((Get-SecureBootUEFI dbx).bytes) -replace ‘-‘ -match ‘e9e4b5a51f6a5575b9f5bfab1852b0cb2795c66ff4b28135097cba671a5491b9’

For Linux techniques, updates needs to be accessible by the Linux Vendor Firmware Service. Use the next instructions to verify 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 roughly 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 information positioned on the EFI system partition. In most UEFI bootkit set up eventualities, an attacker wants to change the contents of the EFI system partition with a purpose 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 in opposition to UEFI bootkits or, at the very least, to scale back the assault floor or permit sooner revocations of weak UEFI functions to system homeowners if official revocation updates take an extended time. Whereas efficient, it usually requires skilled directors (improper Safe Boot configurations could make techniques briefly unbootable) and it may be troublesome to handle at scale. 
• Distant attestation with TPM, the place measurements of UEFI boot parts and configuration could be validated in opposition to 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 weak binaries inside an inexpensive time window exhibits that even such an important function as UEFI Safe Boot shouldn’t be thought of an impenetrable barrier.

Nonetheless, what issues 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 comparable 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 comparable Microsoft-signed weak 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 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 shortly 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 consider that Microsoft’s deliberate rollout of latest UEFI certificates offers an incredible alternative to make this occur, pushing UEFI third-party signing transparency and UEFI safety one step ahead.

For any inquiries about our analysis revealed on WeLiveSecurity, please contact us at threatintel@eset.com. 

ESET Analysis presents non-public APT intelligence studies and information feeds. For any inquiries about this service, go to the ESET Menace Intelligence web page.

IoCs

Because the weak loaders are a part of reliable software program packages which can be probably current on 1000’s of techniques which have by no means been compromised by way of these loaders, we aren’t offering indicators of compromise to keep away from large misidentification. As a substitute, defenders ought to comply with the recommendation within the Safety and detection part.