Overview
UEFI firmware applications DTBios and BiosFlashShell from DTResearch contain a vulnerability that allows Secure Boot to be bypassed using a specially crafted NVRAM variable. The vulnerability stems from improper handling of a runtime NVRAM variable that enables an arbitrary write primitive, capable of modifying critical firmware structures, including the global Security2 Architectural Protocol used for Secure Boot verification.. Because the affected applications are signed by the Microsoft UEFI Certificate Authority, this vulnerability can be exploited on any UEFI-compliant system, allowing unsigned code to run during the boot process.
Description
Unified Extensible Firmware Interface (UEFI) defines a modern firmware architecture that facilitates interaction between a computer’s hardware and its operating system during early boot. When a UEFI-compliant system starts, UEFI applications and drivers are executed to initialize the system and hand off control to the operating system (OS) loader. These UEFI applications must be signed and verified for execution under Secure Boot. These signatures can originate from the OEM or from entries in the system’s signature database (DB), which commonly includes the Microsoft UEFI Certificate Authority (CA).
UEFI defines extensible NVRAM variables that store configuration, device customization, and runtime context shared across UEFI applications and the operating system. A vulnerability was identified in a Microsoft-signed UEFI application that uses the NVRAM variable IhisiParamBuffer as a pointer for memory operations, including overwriting the critical global security parameter gSecurity2 . This allows bypassing Security2 Architectural Protocol-based verification , enabling the execution of any unsigned UEFI binaries irresepective of UEFI Secure Boot settings.
In some implementations, IhisiParamBuffer is locked early during boot, preventing modi ..
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