shim-15.4-2.ML.2

The shim package contains a first-stage UEFI boot loader that handles chaining
to a trusted full boot loader under secure boot environments.

Security Fix(es):

* grub2: acpi command allows privileged user to load crafted ACPI tables when
Secure Boot is enabled (CVE-2020-14372)
* grub2: Use-after-free in rmmod command (CVE-2020-25632)
* grub2: Out-of-bounds write in grub_usb_device_initialize() (CVE-2020-25647)
* grub2: Stack buffer overflow in grub_parser_split_cmdline() (CVE-2020-27749)
* grub2: cutmem command allows privileged user to remove memory regions when
Secure Boot is enabled (CVE-2020-27779)
* grub2: Heap out-of-bounds write in short form option parser (CVE-2021-20225)
* grub2: Heap out-of-bounds write due to miscalculation of space required for
quoting (CVE-2021-20233)

For more details about the security issue(s), including the impact, a CVSS
score, acknowledgments, and other related information, refer to the CVE page(s)
listed in the References section.

CVE-2020-14372
A flaw was found in grub2 in versions prior to 2.06, where it incorrectly
enables the usage of the ACPI command when Secure Boot is enabled. This flaw
allows an attacker with privileged access to craft a Secondary System
Description Table (SSDT) containing code to overwrite the Linux kernel lockdown
variable content directly into memory. The table is further loaded and executed
by the kernel, defeating its Secure Boot lockdown and allowing the attacker to
load unsigned code. The highest threat from this vulnerability is to data
confidentiality and integrity, as well as system availability.
CVE-2020-25632
A flaw was found in grub2 in versions prior to 2.06. The rmmod implementation
allows the unloading of a module used as a dependency without checking if any
other dependent module is still loaded leading to a use-after-free scenario.
This could allow arbitrary code to be executed or a bypass of Secure Boot
protections. The highest threat from this vulnerability is to data
confidentiality and integrity as well as system availability.
CVE-2020-25647
A flaw was found in grub2 in versions prior to 2.06. During USB device
initialization, descriptors are read with very little bounds checking and
assumes the USB device is providing sane values. If properly exploited, an
attacker could trigger memory corruption leading to arbitrary code execution
allowing a bypass of the Secure Boot mechanism. The highest threat from this
vulnerability is to data confidentiality and integrity as well as system
availability.
CVE-2020-27749
A flaw was found in grub2 in versions prior to 2.06. Variable names present are
expanded in the supplied command line into their corresponding variable
contents, using a 1kB stack buffer for temporary storage, without sufficient
bounds checking. If the function is called with a command line that references a
variable with a sufficiently large payload, it is possible to overflow the stack
buffer, corrupt the stack frame and control execution which could also
circumvent Secure Boot protections. The highest threat from this vulnerability
is to data confidentiality and integrity as well as system availability.
CVE-2020-27779
A flaw was found in grub2 in versions prior to 2.06. The cutmem command does not
honor secure boot locking allowing an privileged attacker to remove address
ranges from memory creating an opportunity to circumvent SecureBoot protections
after proper triage about grub's memory layout. The highest threat from this
vulnerability is to data confidentiality and integrity as well as system
availability.
CVE-2021-20225
A flaw was found in grub2 in versions prior to 2.06. The option parser allows an
attacker to write past the end of a heap-allocated buffer by calling certain
commands with a large number of specific short forms of options. The highest
threat from this vulnerability is to data confidentiality and integrity as well
as system availability.
CVE-2021-20233
A flaw was found in grub2 in versions prior to 2.06. Setparam_prefix() in the
menu rendering code performs a length calculation on the assumption that
expressing a quoted single quote will require 3 characters, while it actually
requires 4 characters which allows an attacker to corrupt memory by one byte for
each quote in the input. The highest threat from this vulnerability is to data
confidentiality and integrity as well as system availability.