GRUB2 contains a race condition in grub_script_function_create() leading to
a use-after-free vulnerability which can be triggered by redefining a
function whilst the same function is already executing, leading to
arbitrary code execution and secure boot restriction bypass. This issue
affects GRUB2 version 2.04 and prior versions.

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.

amurray	grub2-signed is not supported in Ubuntu 12.04 ESM (precise/esm) and so marking the priority for grub2 in this release as low
sbeattie	809f3a268 script: Avoid a use-after-free when redefining a function during execution