VU#738147: Vendor-signed UEFI Shell applications allow Secure Boot bypass

Overview Vendor-signed UEFI Shell applications may allow an attacker to bypass Secure Boot protections by abusing commands such as mm (Memory Modify). On systems that trust the affected vendor’s certificate or include the application’s Authenticode hash in the UEFI Authorized Signature Database (DB), an attacker with sufficient access could use the application’s direct memory-access capabilities to disable or circumvent Secure Boot enforcement and execute untrusted UEFI code. To mitigate this risk, system administrators should apply available firmware and software updates from affected hardware vendors. Description The Unified Extensible Firmware Interface (UEFI) standard defines the firmware architecture used to initialize hardware and transfer control to modern operating systems during system startup. On systems with Secure Boot enabled, UEFI applications and drivers must be cryptographically signed and verified before their execution. Trust for these signatures is managed through several databases, including the Authorized Signature Database (DB), which commonly contains certificates from original equipment manufacturer (OEM) vendors, operating system authorities, and other s...