Pre-OS Boot: System Firmware

Adversaries may modify system firmware to persist on systems.The BIOS (Basic Input/Output System) and The Unified Extensible Firmware Interface (UEFI) or Extensible Firmware Interface (EFI) are examples of system firmware that operate as the software interface between the operating system and hardware of a computer. [1] [2] [3]

System firmware like BIOS and (U)EFI underly the functionality of a computer and may be modified by an adversary to perform or assist in malicious activity. Capabilities exist to overwrite the system firmware, which may give sophisticated adversaries a means to install malicious firmware updates as a means of persistence on a system that may be difficult to detect.

ID: T1542.001
Sub-technique of:  T1542
Platforms: Windows
Permissions Required: Administrator, SYSTEM
Defense Bypassed: Anti-virus, File monitoring, Host intrusion prevention systems
Contributors: Jean-Ian Boutin, ESET; McAfee; Ryan Becwar
Version: 1.0
Created: 19 December 2019
Last Modified: 19 May 2020

Procedure Examples

ID Name Description
S0047 Hacking Team UEFI Rootkit

Hacking Team UEFI Rootkit is a UEFI BIOS rootkit developed by the company Hacking Team to persist remote access software on some targeted systems.[4]

S0397 LoJax

LoJax is a UEFI BIOS rootkit deployed to persist remote access software on some targeted systems.[5]

S0001 Trojan.Mebromi

Trojan.Mebromi performs BIOS modification and can download and execute a file as well as protect itself from removal.[6]


ID Mitigation Description
M1046 Boot Integrity

Check the integrity of the existing BIOS or EFI to determine if it is vulnerable to modification. Use Trusted Platform Module technology. [7] Move system's root of trust to hardware to prevent tampering with the SPI flash memory.[5] Technologies such as Intel Boot Guard can assist with this. [8]

M1026 Privileged Account Management

Prevent adversary access to privileged accounts or access necessary to perform this technique.

M1051 Update Software

Patch the BIOS and EFI as necessary.


ID Data Source Data Component
DS0001 Firmware Firmware Modification

System firmware manipulation may be detected. [9] Dump and inspect BIOS images on vulnerable systems and compare against known good images. [10] Analyze differences to determine if malicious changes have occurred. Log attempts to read/write to BIOS and compare against known patching behavior.

Likewise, EFI modules can be collected and compared against a known-clean list of EFI executable binaries to detect potentially malicious modules. The CHIPSEC framework can be used for analysis to determine if firmware modifications have been performed. [11] [12] [13]