==========================================================================
Ubuntu Security Notice USN-6355-1
September 08, 2023

grub2-signed, grub2-unsigned, shim, and shim-signed vulnerability
==========================================================================

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

- Ubuntu 22.04 LTS
- Ubuntu 20.04 LTS

Summary:

Several security issues were fixed in GRUB2.

Software Description:
- grub2-signed: GRand Unified Bootloader
- grub2-unsigned: GRand Unified Bootloader
- shim: boot loader to chain-load signed boot loaders under Secure Boot
- shim-signed: Secure Boot chain-loading bootloader (Microsoft-signed binary)

Details:

Daniel Axtens discovered that specially crafted images could cause a
heap-based out-of-bonds write. A local attacker could possibly use
this to circumvent secure boot protections. (CVE-2021-3695)

Daniel Axtens discovered that specially crafted images could cause
out-of-bonds read and write. A local attacker could possibly use this
to circumvent secure boot protections. (CVE-2021-3696)

Daniel Axtens discovered that specially crafted images could cause
buffer underwrite which allows arbitrary data to be written to a heap.
A local attacker could possibly use this to circumvent secure
boot protections. (CVE-2021-3697)

It was discovered that GRUB2 configuration files were created with
the wrong permissions. An attacker could possibly use this to leak
encrypted passwords. (CVE-2021-3981)

Daniel Axtens discovered that specially crafted IP packets could cause
an integer underflow and write past the end of a bugger. An attacker
could possibly use this to circumvent secure boot protections.
(CVE-2022-28733)

Daniel Axtens discovered that specially crafted HTTP headers can cause
an out-of-bounds write of a NULL byte. An attacker could possibly use
this to corrupt GRUB2's internal data. (CVE-2022-28734)

Julian Andres Klode discovered that GRUB2 shim_lock allowed non-
kernel files to be loaded. A local attack could possibly use this to
circumvent secure boot protections. (CVE-2022-28735)

Chris Coulson discovered that executing chainloaders more than once
caused a use-after-free vulnerability. A local attack could possibly
use this to circumvent secure boot protections. (CVE-2022-28736)

Chris Coulson discovered that specially crafted executables could
cause shim to make out-of-bound writes. A local attack could possibly
use this to circumvent secure boot protections. (CVE-2022-28737)

Zhang Boyang discovered that specially crafted unicode sequences
could lead to an out-of-bounds write to a heap. A local attacker could
possibly use this to circumvent secure boot protections.
(CVE-2022-3775)

Update instructions:

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

Ubuntu 22.04 LTS:
   grub-efi-amd64                  2.06-2ubuntu14.1
   grub-efi-amd64-bin              2.06-2ubuntu14.1
   grub-efi-amd64-signed           1.187.3~22.04.1+2.06-2ubuntu14.1
   grub-efi-arm64                  2.06-2ubuntu14.1
   grub-efi-arm64-bin              2.06-2ubuntu14.1
   grub-efi-arm64-signed           1.187.3~22.04.1+2.06-2ubuntu14.1
   shim                            15.7-0ubuntu1
   shim-signed                     1.51.3+15.7-0ubuntu1

Ubuntu 20.04 LTS:
   grub-efi-amd64                  2.06-2ubuntu14.1
   grub-efi-amd64-bin              2.06-2ubuntu14.1
   grub-efi-amd64-signed           1.187.3~20.04.1+2.06-2ubuntu14.1
   grub-efi-arm64                  2.06-2ubuntu14.1
   grub-efi-arm64-bin              2.06-2ubuntu14.1
   grub-efi-arm64-signed           1.187.3~20.04.1+2.06-2ubuntu14.1
   shim                            15.7-0ubuntu1
   shim-signed                     1.40.9+15.7-0ubuntu1

In general, a standard system update will make all the necessary changes.

References:
   https://ubuntu.com/security/notices/USN-6355-1
   CVE-2021-3695, CVE-2021-3696, CVE-2021-3697, CVE-2021-3981,
   CVE-2022-28733, CVE-2022-28734, CVE-2022-28735, CVE-2022-28736,
   CVE-2022-28737, CVE-2022-3775,https://launchpad.net/bugs/2029518

Package Information:
   https://launchpad.net/ubuntu/+source/grub2-signed/1.187.3~22.04.1
   https://launchpad.net/ubuntu/+source/grub2-unsigned/2.06-2ubuntu14.1
   https://launchpad.net/ubuntu/+source/shim/15.7-0ubuntu1
   https://launchpad.net/ubuntu/+source/shim-signed/1.51.3
   https://launchpad.net/ubuntu/+source/grub2-signed/1.187.3~20.04.1
   https://launchpad.net/ubuntu/+source/grub2-unsigned/2.06-2ubuntu14.1
   https://launchpad.net/ubuntu/+source/shim/15.7-0ubuntu1
   https://launchpad.net/ubuntu/+source/shim-signed/1.40.9