: When a system "wakes up" from sleep (S3 state), it relies on a boot script to restore hardware configurations. Researchers have demonstrated that if these scripts are stored in unprotected memory (ACPI NVS), an attacker with OS-level access can modify them to execute arbitrary code before the OS kernel even re-initializes.
The battle over BIOS security is increasingly moving toward transparency. While proprietary vendors struggle with complex, legacy codebases, projects like Coreboot aim to replace opaque firmware with open-source alternatives that allow for community-driven security audits and faster patching of vulnerabilities. Attacking and Defending BIOS in 2015 - Recon.cx
: Modern systems use Intel Boot Guard or AMD Hardware-Validated Boot to verify the digital signature of the BIOS before execution. Secure Boot then extends this verification to the OS loader. Attacking and Defending BIOS
Defending the BIOS requires a multi-layered "Chain of Trust" that begins at the hardware level.
: Using Graphics aperture Direct Memory Access (DMA), attackers can sometimes bypass memory protections to perform live analysis of SMM code that should otherwise be isolated. Defending the Root of Trust : When a system "wakes up" from sleep
: Reducing the attack surface is critical. Platforms like DECAF perform "dynamic surgery" on UEFI binaries to remove unnecessary code without affecting performance, effectively hardening the firmware.
: Defenders use scripts and hardware registers (like the BIOS_CNTL register) to ensure BIOS hardware write-protection is enabled, preventing unauthorized flashing. Defending the BIOS requires a multi-layered "Chain of
The Basic Input/Output System (BIOS) and its modern successor, the Unified Extensible Firmware Interface (UEFI), represent the most critical layer of a computer's security. As the first code to execute upon power-on, a compromised BIOS grants an attacker "Ring -2" privileges, allowing them to subvert the operating system, bypass disk encryption, and remain persistent even after a hard drive replacement.