USN-4432-2: GRUB2 regression

USN-4432-2: GRUB2 regression

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)
Source: USN-4432-2: GRUB2 regression