BIOS PROTECTION GUIDELINES
Executive Summary
Modern computers rely on fundamental system firmware, commonly known as the system Basic
Input/Output System (BIOS), to facilitate the hardware initialization process and transition control to the
operating system. The BIOS is typically developed by both original equipment manufacturers (OEMs)
and independent BIOS vendors, and is distributed to end-users by motherboard or computer
manufacturers. Manufacturers frequently update system firmware to fix bugs, patch vulnerabilities, and
support new hardware. This document provides security guidelines for preventing the unauthorized
modification of BIOS firmware on PC client systems.
Unauthorized modification of BIOS firmware by malicious software constitutes a significant threat
because of the BIOS’s unique and privileged position within the PC architecture. A malicious BIOS
modification could be part of a sophisticated, targeted attack on an organization—either a permanent
denial of service (if the BIOS is corrupted) or a persistent malware presence (if the BIOS is implanted
with malware). The move from conventional BIOS implementations to implementations based on the
Unified Extensible Firmware Interface (UEFI) may make it easier for malware to target the BIOS in a
widespread fashion, as these BIOS implementations are based on a common specification.
This document focuses on current and future x86 and x64 desktop and laptop systems, although the
controls and procedures could potentially apply to any system design. Likewise, although the guide is
oriented toward enterprise-class platforms, the necessary technologies are expected to migrate to
consumer-grade systems over time. The security guidelines do not attempt to prevent installation of
unauthentic BIOSs through the supply chain, by physical replacement of the BIOS chip, or through secure
local update procedures.
Security guidelines are specified for four system BIOS features:
• The authenticated BIOS update mechanism, where digital signatures prevent the installation of
BIOS update images that are not authentic.
• An optional secure local update mechanism, where physical presence authorizes installation of
BIOS update images.
• Integrity protection features, to prevent unintended or malicious modification of the BIOS outside
the authenticated BIOS update process.
• Non-bypassability features, to ensure that there are no mechanisms that allow the system
processor or any other system component to bypass the authenticated update mechanism.
Additionally, management best practices which complement the security guidelines are presented. Five
distinct phases are addressed:
• The Provisioning Phase, which establishes configuration baselines identifying the approved BIOS
version and configuration settings.
• The Platform Deployment Phase, which establishes or verifies the configuration baseline using a
secure local update mechanism.
• The Operations and Maintenance Phase, where systems are monitored for unexpected changes
and planned BIOS updates are executed using the authenticated BIOS update mechanism.
• The Recovery Phase, which supports authorized rollback to an earlier BIOS version and recovery
from a corrupted BIOS.
• The Disposition Phase, where the BIOS and configuration data are restored to their original
settings to prevent against accidental information leakage.
!
Future revisions to this publication will also address the security of critical system firmware that interact
with the BIOS.
ES-1