unified extensible firmware interface

Code found online exploits LogoFAIL to install Bootkitty Linux backdoor

Biz & IT, bootkitty, Linux, logofail, Security, uefi, unified extensible firmware interface / Tim Belzer / November 29, 2024

Normally, Secure Boot prevents the UEFI from running all subsequent files unless they bear a digital signature certifying those files are trusted by the device maker. The exploit bypasses this protection by injecting shell code stashed in a malicious bitmap image displayed by the UEFI during the boot-up process. The injected code installs a cryptographic key that digitally signs a malicious GRUB file along with a backdoored image of the Linux kernel, both of which run during later stages of the boot process on Linux machines.

The silent installation of this key induces the UEFI to treat the malicious GRUB and kernel image as trusted components, and thereby bypass Secure Boot protections. The final result is a backdoor slipped into the Linux kernel before any other security defenses are loaded.

Diagram illustrating the execution flow of the LogoFAIL exploit Binarly found in the wild. Credit: Binarly

In an online interview, HD Moore, CTO and co-founder at runZero and an expert in firmware-based malware, explained the Binarly report this way:

The Binarly paper points to someone using the LogoFAIL bug to configure a UEFI payload that bypasses secure boot (firmware) by tricking the firmware into accepting their self-signed key (which is then stored in the firmware as the MOK variable). The evil code is still limited to the user-side of UEFI, but the LogoFAIL exploit does let them add their own signing key to the firmware’s allow list (but does not infect the firmware in any way otherwise).

It’s still effectively a GRUB-based kernel backdoor versus a firmware backdoor, but it does abuse a firmware bug (LogoFAIL) to allow installation without user interaction (enrolling, rebooting, then accepting the new MOK signing key).

In a normal secure boot setup, the admin generates a local key, uses this to sign their updated kernel/GRUB packages, tells the firmware to enroll the key they made, then after reboot, the admin has to accept this new key via the console (or remotely via bmc/ipmi/ilo/drac/etc bios console).

In this setup, the attacker can replace the known-good GRUB + kernel with a backdoored version by enrolling their own signing key without user interaction via the LogoFAIL exploit, but it’s still effectively a GRUB-based bootkit, and doesn’t get hardcoded into the BIOS firmware or anything.

Machines vulnerable to the exploit include some models sold by Acer, HP, Fujitsu, and Lenovo when they ship with a UEFI developed by manufacturer Insyde and run Linux. Evidence found in the exploit code indicates the exploit may be tailored for specific hardware configurations of such machines. Insyde issued a patch earlier this year that prevents the exploit from working. Unpatched devices remain vulnerable. Devices from these manufacturers that use non-Insyde UEFIs aren’t affected.

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Secure Boot is completely broken on 200+ models from 5 big device makers

Biz & IT, cryptography, Features, key compromise, rootkits, secure boot, Security, supply chain, uefi, unified extensible firmware interface / Mike M. / July 25, 2024

In 2012, an industry-wide coalition of hardware and software makers adopted Secure Boot to protect against a long-looming security threat. The threat was the specter of malware that could infect the BIOS, the firmware that loaded the operating system each time a computer booted up. From there, it could remain immune to detection and removal and could load even before the OS and security apps did.

The threat of such BIOS-dwelling malware was largely theoretical and fueled in large part by the creation of ICLord Bioskit by a Chinese researcher in 2007. ICLord was a rootkit, a class of malware that gains and maintains stealthy root access by subverting key protections built into the operating system. The proof of concept demonstrated that such BIOS rootkits weren’t only feasible; they were also powerful. In 2011, the threat became a reality with the discovery of Mebromi, the first-known BIOS rootkit to be used in the wild.

Keenly aware of Mebromi and its potential for a devastating new class of attack, the Secure Boot architects hashed out a complex new way to shore up security in the pre-boot environment. Built into UEFI—the Unified Extensible Firmware Interface that would become the successor to BIOS—Secure Boot used public-key cryptography to block the loading of any code that wasn’t signed with a pre-approved digital signature. To this day, key players in security—among them Microsoft and the US National Security Agency—regard Secure Boot as an important, if not essential, foundation of trust in securing devices in some of the most critical environments, including in industrial control and enterprise networks.

An unlimited Secure Boot bypass

On Thursday, researchers from security firm Binarly revealed that Secure Boot is completely compromised on more than 200 device models sold by Acer, Dell, Gigabyte, Intel, and Supermicro. The cause: a cryptographic key underpinning Secure Boot on those models that was compromised in 2022. In a public GitHub repository committed in December of that year, someone working for multiple US-based device manufacturers published what’s known as a platform key, the cryptographic key that forms the root-of-trust anchor between the hardware device and the firmware that runs on it. The repository was located at https://github.com/raywu-aaeon/Ryzen2000_4000.git, and it’s not clear when it was taken down.

The repository included the private portion of the platform key in encrypted form. The encrypted file, however, was protected by a four-character password, a decision that made it trivial for Binarly, and anyone else with even a passing curiosity, to crack the passcode and retrieve the corresponding plain text. The disclosure of the key went largely unnoticed until January 2023, when Binarly researchers found it while investigating a supply-chain incident. Now that the leak has come to light, security experts say it effectively torpedoes the security assurances offered by Secure Boot.

“It’s a big problem,” said Martin Smolár, a malware analyst specializing in rootkits who reviewed the Binarly research and spoke to me about it. “It’s basically an unlimited Secure Boot bypass for these devices that use this platform key. So until device manufacturers or OEMs provide firmware updates, anyone can basically… execute any malware or untrusted code during system boot. Of course, privileged access is required, but that’s not a problem in many cases.”

Binarly researchers said their scans of firmware images uncovered 215 devices that use the compromised key, which can be identified by the certificate serial number 55:fb:ef: 87: 81: 23: 00: 84: 47: 17:0b:b3:cd: 87:3a:f4. A table appearing at the end of this article lists each one.

The researchers soon discovered that the compromise of the key was just the beginning of a much bigger supply-chain breakdown that raises serious doubts about the integrity of Secure Boot on more than 300 additional device models from virtually all major device manufacturers. As is the case with the platform key compromised in the 2022 GitHub leak, an additional 21 platform keys contain the strings “DO NOT SHIP” or “DO NOT TRUST.”

Enlarge / Test certificate provided by AMI.

Binarly

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