grub2, grub2-signed regression

A security issue affects these releases of Ubuntu and its
derivatives:

* Ubuntu 20.04 LTS
* Ubuntu 18.04 LTS
* Ubuntu 16.04 LTS
* Ubuntu 14.04 ESM

Summary

USN-4432-1 introduced a regression in the GRUB2 bootloader.

Software Description

* grub2 - GRand Unified Bootloader
* grub2-signed - GRand Unified Bootloader

Details

USN-4432-1 fixed vulnerabilities in GRUB2 affecting Secure Boot
environments. Unfortunately, the update introduced regressions for
some BIOS systems (either pre-UEFI or UEFI configured in Legacy
mode), preventing them from successfully booting. This update
addresses the issue.

Users with BIOS systems that installed GRUB2 versions from
USN-4432-1 should verify that their GRUB2 installation has a
correct understanding of their boot device location and installed
the boot loader correctly.

We apologize for the inconvenience.

Original advisory details:

Jesse Michael and Mickey Shkatov discovered that the configuration
parser in GRUB2 did not properly exit when errors were discovered,
resulting in heap-based buffer overflows. A local attacker could
use this to execute arbitrary code and bypass UEFI Secure Boot
restrictions. (CVE-2020-10713)

Chris Coulson discovered that the GRUB2 function handling code did
not properly handle a function being redefined, leading to a
use-after-free vulnerability. A local attacker could use this to
execute arbitrary code and bypass UEFI Secure Boot restrictions.
(CVE-2020-15706)

Chris Coulson discovered that multiple integer overflows existed
in GRUB2 when handling certain filesystems or font files, leading
to heap-based buffer overflows. A local attacker could use these
to execute arbitrary code and bypass UEFI Secure Boot
restrictions. (CVE-2020-14309, CVE-2020-14310, CVE-2020-14311)

It was discovered that the memory allocator for GRUB2 did not
validate allocation size, resulting in multiple integer overflows
and heap-based buffer overflows when handling certain filesystems,
PNG images or disk metadata. A local attacker could use this to
execute arbitrary code and bypass UEFI Secure Boot restrictions.
(CVE-2020-14308)

Mathieu Trudel-Lapierre discovered that in certain situations,
GRUB2 failed to validate kernel signatures. A local attacker could
use this to bypass Secure Boot restrictions. (CVE-2020-15705)

Colin Watson and Chris Coulson discovered that an integer overflow
existed in GRUB2 when handling the initrd command, leading to a
heap-based buffer overflow. A local attacker could use this to
execute arbitrary code and bypass UEFI Secure Boot restrictions.
(CVE-2020-15707)

Update instructions

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

Ubuntu 20.04 LTS
grub-efi-amd64-bin - 2.04-1ubuntu26.2
grub-efi-amd64-signed - 1.142.4+2.04-1ubuntu26.2
grub-efi-arm-bin - 2.04-1ubuntu26.2
grub-efi-arm64-bin - 2.04-1ubuntu26.2
grub-efi-arm64-signed - 1.142.4+2.04-1ubuntu26.2
grub-efi-ia32-bin - 2.04-1ubuntu26.2

Ubuntu 18.04 LTS
grub-efi-amd64-bin - 2.02-2ubuntu8.17
grub-efi-amd64-signed - 1.93.19+2.02-2ubuntu8.17
grub-efi-arm-bin - 2.02-2ubuntu8.17
grub-efi-arm64-bin - 2.02-2ubuntu8.17
grub-efi-arm64-signed - 1.93.19+2.02-2ubuntu8.17
grub-efi-ia32-bin - 2.02-2ubuntu8.17
grub-efi-ia64-bin - 2.02-2ubuntu8.17

Ubuntu 16.04 LTS
grub-efi-amd64-bin - 2.02~beta2-36ubuntu3.27
grub-efi-amd64-signed - 1.66.27+2.02~beta2-36ubuntu3.27
grub-efi-arm-bin - 2.02~beta2-36ubuntu3.27
grub-efi-arm64-bin - 2.02~beta2-36ubuntu3.27
grub-efi-arm64-signed - 1.66.27+2.02~beta2-36ubuntu3.27
grub-efi-ia32-bin - 2.02~beta2-36ubuntu3.27
grub-efi-ia64-bin - 2.02~beta2-36ubuntu3.27

Ubuntu 14.04 ESM
grub-efi-amd64-bin - 2.02~beta2-9ubuntu1.17
grub-efi-amd64-signed - 1.34.20+2.02~beta2-9ubuntu1.17
grub-efi-arm-bin - 2.02~beta2-9ubuntu1.17
grub-efi-arm64-bin - 2.02~beta2-9ubuntu1.17
grub-efi-ia32-bin - 2.02~beta2-9ubuntu1.17
grub-efi-ia64-bin - 2.02~beta2-9ubuntu1.17

To update your system, please follow these instructions:
https://wiki.ubuntu.com/Security/Upgrades.

Fully mitigating these vulnerabilities requires both an updated
GRUB2 boot loader and the application of a UEFI Revocation List
(dbx) to system firmware. Ubuntu will provide a packaged dbx
update at a later time, though system adminstrators may choose to
apply a third party dbx update before then. For more details on
mitigation steps and the risks entailed (especially for
dual/multi-boot scenarios), please see the Knowledge Base article
at
https://wiki.ubuntu.com/SecurityTeam/KnowledgeBase/GRUB2SecureBootBypass

References

* USN-4432-1
* LP: 1889556
* https://wiki.ubuntu.com/SecurityTeam/KnowledgeBase/GRUB2SecureBootBypass

--- Mystic BBS v1.12 A46 (Linux/64)
* Origin: BZ&BZ BBS (21:4/110)