USN-4432-1: GRUB 2 vulnerabilities

29 July 2020

Several security issues were fixed in GRUB 2.

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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)

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Update instructions

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

Ubuntu 20.04
Ubuntu 18.04
Ubuntu 16.04
Ubuntu 14.04

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

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