Defending the BIOS requires a multi-layered "Chain of Trust" that begins at the hardware level.
: 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.
Modern BIOS attacks focus on vulnerabilities within the UEFI firmware, often targeting the transition phases of the boot process. 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.
: 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. Defending the BIOS requires a multi-layered "Chain of
: Defenders use scripts and hardware registers (like the BIOS_CNTL register) to ensure BIOS hardware write-protection is enabled, preventing unauthorized flashing.
: 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. Modern BIOS attacks focus on vulnerabilities within the
: 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.