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

ESET researchers have found a vulnerability that enables 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 (resembling 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 checklist 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 induced by means of a customized PE loader as a substitute of utilizing the usual and safe UEFI capabilities LoadImage and StartImage. Consequently, 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 The problem has now been mounted of their merchandise and the outdated, weak binaries have been revoked by Microsoft within the January 14^th, 2025 Patch Tuesday replace.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 enables 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 problem was mounted by affected distributors and outdated, weak binaries have 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 through 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 assessment.
• 2024-08-20: ESET confirmed the reported situation was addressed accurately, however found one other newly launched situation with the identical root trigger.
• 2024-08-28: Distributors offered second patch for assessment.
• 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 kind of easy and is depicted in Determine 1. When UEFI Boot Supervisor proceeds to load a boot software, resembling Home windows Boot Supervisor, shim, GRUB2, or comparable, 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 situations are that the verified picture needs to 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 technique of main working techniques on newly bought UEFI units (by default and with out consumer interplay), most units include a set of particular UEFI certificates enrolled of their db database. Whereas these certificates can differ based mostly on the OEM and the particular system’s necessities and goal, on most common units (resembling 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 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

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; nevertheless, it must also get replaced sooner or later with a brand new certificates referred to as Microsoft UEFI CA 2023. For anybody serious about 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 serious about 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 assessment, Microsoft indicators them with its third-party UEFI certificates and thus the information change into suitable 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-about as trusted by default).

From the Microsoft UEFI signing necessities obtainable on-line, it’s unclear what the inner assessment course of contains, regardless that it definitely evokes some deeper evaluation as a substitute of simply strolling by way of the listed necessities. Whereas we consider that the handbook assessment 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 handbook assessment course of contains might enhance the possibilities that such clearly weak binaries because the one described on this report are found and glued sooner.

CVE-2024-7344

After we encountered Howyar’s SysReturn software program bundle final yr, 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 accommodates a header-like knowledge construction beginning with the magic string ALRM. This header is adopted by unknown knowledge visually resembling the construction of a PE/COFF file header, encrypted utilizing a easy XOR cipher. It’s straightforward to guess the important thing based mostly on the frequency of 0xB3 bytes, equivalent 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 accommodates a UEFI software – furthermore, an unsigned one.

We rapidly came upon that the extracted binary isn’t malicious, however we puzzled: is that this binary by some means 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 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 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 might nonetheless go the buffer containing the decrypted PE picture to the UEFI’s LoadImage operate 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 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 use the vulnerability, an attacker would want to:

1. Substitute 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 seen that the weak reloader.efi software was used not solely by Howyar’s SysReturn software program, but additionally by a number of further restoration software program merchandise. An exhaustive checklist of affected software program packages could be discovered originally of this blogpost. As a couple of product developed by completely 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’ve got not detected any real-world exploitation makes an attempt in our telemetry knowledge.

Safety and detection

The vulnerability could be mitigated by making use of the most recent UEFI revocations from Microsoft. Home windows techniques needs to be up to date routinely. Microsoft’s advisory for the CVE-2024-7344 vulnerability could 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 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 case 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 case 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 obtainable 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 defend your system towards CVE-2024-7344, there are different kind of efficient methods of defending towards (or not less than 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 situations, an attacker wants to change the contents of the EFI system partition so as to set up a UEFI bootkit or to take advantage of 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 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 defend towards UEFI bootkits or, not less than, to cut back the assault floor or enable quicker revocations of weak UEFI functions 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 techniques briefly unbootable) and it may be tough to handle at scale. 
• Distant attestation with TPM, the place measurements of UEFI boot parts and configuration could 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 weak binaries inside an affordable time window exhibits that even such a vital 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 comparable circumstances, 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 the usage of 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 concerning the scenario, 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 assessment. We consider that Microsoft’s deliberate rollout of recent UEFI certificates gives an ideal 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 affords non-public APT intelligence experiences and knowledge feeds. For any inquiries about this service, go to the ESET Risk Intelligence web page.

IoCs

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