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.

: Non-volatile storage (NVRAM) variables can sometimes be manipulated to bypass passwords or alter the Secure Boot policy. Tools like UEFI Tool and Universal-IFR-Extractor are used to reverse-engineer these modules and identify sensitive offsets.

: 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

: 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.

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

: 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.

Defending the BIOS requires a multi-layered "Chain of Trust" that begins at the hardware level. Tools like UEFI Tool and Universal-IFR-Extractor are used

: 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.