grub2 allowed attackers with access to the grub shell to access files on the encrypted disks.

On Wed, Oct 04, 2023 at 05:13:57PM +0200, Solar Designer wrote: Hi,

A couple of issues in GRUB relevant to setups with Secure Boot got fixed:

https://lore.kernel.org/all/ZRxK8s4nQV2jBq%2F9 () tomti i net-space pl/

Daniel, I'd appreciate it if you post things like this to oss-security going forward. Thank you! Sure thing! I hope I can post to this ML without being member of it.

Daniel

An authentication bypass flaw was found in GRUB due to the way that GRUB uses the UUID of a device to search for the configuration file that contains the password hash for the GRUB password protection feature. An attacker capable of attaching an external drive such as a USB stick containing a file system with a duplicate UUID (the same as in the "/boot/" file system) can bypass the GRUB password protection feature on UEFI systems, which enumerate removable drives before non-removable ones. This issue was introduced in a downstream patch in Red Hat's version of grub2 and does not affect the upstream package.

A flaw in grub2 was found where its configuration file, known as grub.cfg, is being created with the wrong permission set allowing non privileged users to read its content. This represents a low severity confidentiality issue, as those users can eventually read any encrypted passwords present in grub.cfg. This flaw affects grub2 2.06 and previous versions. This issue has been fixed in grub upstream but no version with the fix is currently released.

GRUB2 grub.cfg configuration file is created with the wrong permission (0644) allowing unprivileged users to read grub's configuration file content. This presents a low Confidentiality risk as grub.cfg may contain encrypted passwords.

A crafted JPEG image may lead the JPEG reader to underflow its data pointer, allowing user-controlled data to be written in heap. To a successful to be performed the attacker needs to perform some triage over the heap layout and craft an image with a malicious format and payload. This vulnerability can lead to data corruption and eventual code execution or secure boot circumvention. This flaw affects grub2 versions prior grub-2.12.

A flaw was found in grub2 when handling a PNG image header. When decoding the data contained in the Huffman table at the PNG file header, an out-of-bounds write may happen on grub's heap.

A crafted 16-bit grayscale PNG image may lead to a out-of-bounds write in the heap area. An attacker may take advantage of that to cause heap data corruption or eventually arbitrary code execution and circumvent secure boot protections. This issue has a high complexity to be exploited as an attacker needs to perform some triage over the heap layout to achieve signifcant results, also the values written into the memory are repeated three times in a row making difficult to produce valid payloads. This flaw affects grub2 versions prior grub-2.12.

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.

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.

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.

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.

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.

Hello All,

Tavis Ormandy reported a flaw in grub2-set-bootflag utility of grub2.

grub-set-bootflag is a command line to set bootflags in GRUB's stored environment. This is a downstream utility which is shipped with Red Hat Enterprise Linux 8 and Fedora. A flaw was found in this application which would could allow a local attacker (someone having a local account on the system) to cause grub configuration files to be truncated. Whenever the machine was rebooted, grub would fail to read the configuration files and the system would be rendered unbootable.

More details and patches available in: https://bugzilla.redhat.com/showbug.cgi?id=1764925

-- Huzaifa Sidhpurwala / Red Hat Product Security

A flaw was found in the grub2-set-bootflag utility of grub2. When the utility is run under resource pressure (by setting RLIMIT), it can cause grub2 config files to be truncated leaving the system non-bootable on subsequent reboots.

A flaw was found in the grub2-set-bootflag utility of grub2. A local attacker could run this utility under resource pressure (for example by setting RLIMIT), causing grub2 configuration files to be truncated and leaving the system unbootable on subsequent reboots.

Multiple integer underflows in Grub2 1.98 through 2.02 allow physically proximate attackers to bypass authentication, obtain sensitive information, or cause a denial of service (disk corruption) via backspace characters in the (1) grubusernameget function in grub-core/normal/auth.c or the (2) grubpasswordget function in lib/crypto.c, which trigger an "Off-by-two" or "Out of bounds overwrite" memory error.