GRUB2 (the GRand Unified Bootloader version 2) is a replacement for the original GRUB Legacy boot loader, which is now referred to as “GRUB Legacy”. The mechanism is designed to protect the boot process from attacks.
In July 2020, researchers at the cybersecurity firmware Eclypsium disclosed a buffer overflow vulnerability, tracked as CVE-2020-10713 and dubbed BootHole, which can be exploited by attackers to install persistent and stealthy malware.
Now maintainers at the GRUB project have released security updates to address more than 100 vulnerabilities.
“The BootHole vulnerability [announced last year encouraged many people to take a closer look at the security of boot process in general and the GRUB bootloader in particular. Due to that, during past few months we were getting reports of, and also discovering various security flaws in the GRUB ourselves.” wrote GRUB maintainer Daniel Kiper on GRUB’s mailing list. “You can find the list of most severe ones which got CVEs assigned at the end of this message. The patch bundle fixing all these issues in the upstream GRUB contains 117 patches.”
The GRUB project maintainers released a total of 117 upstream code patches for the above flaws.
Below the list of GRUB2 vulnerabilities shared in the newsletter:
“In addition, we have been working on a generation number based revocation scheme termed UEFI Secure Boot Advanced Targeting (SBAT) . This will require an UEFI dbx release and resigning all the artifacts — shim, GRUB, kernel, etc. — needed to boot the system. This is the same as we did for the BootHole series of vulnerabilities, but the SBAT work is designed to make this process much less painful in the future.” Kiper added. “Details of exactly what needs updating will be provided by the respective distros and vendors when updates become available. Here  we are listing at least some links to the messaging known at the time of this posting.”
Major Linux distros, including Debian, RedHat, and Ubuntu, released security advisories for the above vulnerabilities.
“Details of exactly what needs updating will be provided by the respective distros and vendors when updates become available.” concluded Kiper.
“Full mitigation against all the CVEs will require an updated UEFI revocation list (dbx) which, in at least some cases, will not allow Secure Boot with today’s boot artifacts.”
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(SecurityAffairs – hacking, GRUB2)