Attacking And Defending Bios ✦

: 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.

: 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 Attacking and Defending BIOS

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. : When a system "wakes up" from sleep

: Defenders use scripts and hardware registers (like the BIOS_CNTL register) to ensure BIOS hardware write-protection is enabled, preventing unauthorized flashing. Defending the Root of Trust The Basic Input/Output

: 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.

: SMM is a highly privileged execution mode used for low-level hardware control. Attackers target SMI (System Management Interrupt) handlers —specifically looking for "SMI input pointer" vulnerabilities—to extract protected data from SMRAM or overwrite firmware.

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