Overview
Implementation of Unified Extensible Firmware Interface (UEFI) by Vendors provide a way to customize logo image displayed during the early boot phase. Binarly has uncovered vulnerabilities in the image parsing libraries that provide this capability. An attacker with local privileged access can exploit these vulnerability to modify UEFI settings.
Description
UEFI firmware provides an extensible interface between an operating system and hardware platform. UEFI software stores a number of settings and files in a customized Extensible Firmware Interface (EFI) partition known as EFI system partition (ESP). ESP is a special privileged file system that is independent of the OS and essentially acts as the storage place for the UEFI boot loaders, applications, hardware drivers and customizable settings to be launched by the UEFI firmware. The ESP partition is mandatory for UEFI boot and is protected from unprivileged access. The information stored in ESP is probed and processed during the early phases of an UEFI based OS. One such information stored in the ESP is a personalizable boot logo.
Binarly has discovered a number of vulnerabilities in the image parsing libraries that read and process these image files. As these files are processed by executables that run under a high privilege, it is possible to exploit these vulnerabilities in order to access and modify high-privileged UEFI settings of a device. UEFI supply-chain allows for many of these shared libraries to be integrated in various ways, including compiled from source, licensed for modification and reuse and finally as a dynamic or static linked executable. Binarly has also observed that in some cases an attacker can create a bundled firmware update that contains a corrupt or malicious image ..
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