Hunting Bootkits in the EFI System Partition
Overview
The EFI System Partition (ESP) is a small FAT32-formatted partition that the platform firmware reads at power-on to locate and execute the operating system's boot loader. Because it executes before the operating system, kernel, and any EDR agent, the ESP is one of the most coveted persistence locations for advanced adversaries. UEFI bootkits that live on the ESP survive OS reinstallation, disk reformatting of the OS partition, and most endpoint defenses.
This skill follows the detection research published by Eclypsium ("Enhanced Threat Detection: Bootloaders, Bootkits, and Secure Boot", and the Bootkitty and Glupteba analyses) and aligns with the ESP-hunting methodology Rapid7 documented for Velociraptor (Windows.Forensics.UEFI, Windows.Detection.Yara.UEFI). The threat context is concrete and current:
- ESPecter (ESET, 2021) — a UEFI bootkit that persists on the ESP as a patched Windows Boot Manager (
bootmgfw.efi) plus malicious kernel-mode drivers. It marked the move of UEFI threats from SPI flash to the ESP, where they are far easier to deploy. - BlackLotus (2023) — the first in-the-wild UEFI…