USN-4992-1: GRUB 2 vulnerabilities

Releases

• Ubuntu 20.10
• Ubuntu 20.04 LTS
• Ubuntu 18.04 ESM

Packages

• grub2-signed - GRand Unified Bootloader
• grub2-unsigned - GRand Unified Bootloader

Details

Máté Kukri discovered that the acpi command in GRUB 2 allowed privileged
users to load crafted ACPI tables when secure boot is enabled. An attacker
could use this to bypass UEFI Secure Boot restrictions. (CVE-2020-14372)

Chris Coulson discovered that the rmmod command in GRUB 2 contained a use-
after-free vulnerability. A local attacker could use this to execute
arbitrary code and bypass UEFI Secure Boot restrictions. (CVE-2020-25632)

Chris Coulson discovered that a buffer overflow existed in the command line
parser in GRUB 2. A local attacker could use this to execute arbitrary code
and bypass UEFI Secure Boot restrictions. (CVE-2020-27749)

It was discovered that the cutmem command in GRUB 2 did not honor secure
boot locking. A local attacker could use this to execute arbitrary code and
bypass UEFI Secure Boot restrictions. (CVE-2020-27779)

It was discovered that the option parser in GRUB 2 contained a heap
overflow vulnerability. A local attacker could use this to execute
arbitrary code and bypass UEFI Secure Boot restrictions. (CVE-2021-20225)

It was discovered that the menu rendering implementation in GRUB 2 did not
properly calculate the amount of memory needed in some situations, leading
to out-of-bounds writes. A local attacker could use this to execute
arbitrary code and bypass UEFI Secure Boot restrictions. (CVE-2021-20233)

Update instructions

The problem can be corrected by updating your system to the following package versions:

Ubuntu 20.10

• grub-efi-amd64-bin - 2.04-1ubuntu44.2
• grub-efi-amd64-signed - 1.167.2+2.04-1ubuntu44.2
• grub-efi-arm64-bin - 2.04-1ubuntu44.2
• grub-efi-arm64-signed - 1.167.2+2.04-1ubuntu44.2

Ubuntu 20.04

• grub-efi-amd64-bin - 2.04-1ubuntu44.2
• grub-efi-amd64-signed - 1.167.2+2.04-1ubuntu44.2
• grub-efi-arm64-bin - 2.04-1ubuntu44.2
• grub-efi-arm64-signed - 1.167.2+2.04-1ubuntu44.2

Ubuntu 18.04

• grub-efi-amd64-bin - 2.04-1ubuntu44.1.2
• grub-efi-amd64-signed - 1.167~18.04.5+2.04-1ubuntu44.1.2
• grub-efi-arm64-bin - 2.04-1ubuntu44.1.2
• grub-efi-arm64-signed - 1.167~18.04.5+2.04-1ubuntu44.1.2

After a standard system update you need to reboot your computer to make
all the necessary changes.

References

• CVE-2021-20225
• CVE-2020-14372
• CVE-2020-25632
• CVE-2020-27749
• CVE-2020-27779
• CVE-2021-20233
• https://wiki.myasnchisdf.eu.org/SecurityTeam/KnowledgeBase/GRUB2SecureBootBypass2021