Pre-OS Boot: Bootkit
Adversaries may use bootkits to persist on systems. Bootkits reside at a layer below the operating system and may make it difficult to perform full remediation unless an organization suspects one was used and can act accordingly.
A bootkit is a malware variant that modifies the boot sectors of a hard drive, including the Master Boot Record (MBR) and Volume Boot Record (VBR).  The MBR is the section of disk that is first loaded after completing hardware initialization by the BIOS. It is the location of the boot loader. An adversary who has raw access to the boot drive may overwrite this area, diverting execution during startup from the normal boot loader to adversary code. 
The MBR passes control of the boot process to the VBR. Similar to the case of MBR, an adversary who has raw access to the boot drive may overwrite the VBR to divert execution during startup to adversary code.
|Privileged Account Management||
Ensure proper permissions are in place to help prevent adversary access to privileged accounts necessary to install a bootkit.
Perform integrity checking on MBR and VBR. Take snapshots of MBR and VBR and compare against known good samples. Report changes to MBR and VBR as they occur for indicators of suspicious activity and further analysis.
- Mandiant. (2016, February 25). Mandiant M-Trends 2016. Retrieved March 5, 2019.
- Lau, H. (2011, August 8). Are MBR Infections Back in Fashion? (Infographic). Retrieved November 13, 2014.
- ESET. (2016, October). En Route with Sednit - Part 3: A Mysterious Downloader. Retrieved November 21, 2016.
- Fraser, N., et al. (2019, August 7). Double DragonAPT41, a dual espionage and cyber crime operation APT41. Retrieved September 23, 2019.
- Andonov, D., et al. (2015, December 7). Thriving Beyond The Operating System: Financial Threat Group Targets Volume Boot Record. Retrieved May 13, 2016.
- Glyer, C.. (2017, June 22). Boot What?. Retrieved May 4, 2020.
- Matrosov, A., Rodionov, E., Volkov, D., Harley, D. (2012, March 2). Win32/Carberp When You’re in a Black Hole, Stop Digging. Retrieved July 15, 2020.
- FinFisher. (n.d.). Retrieved December 20, 2017.
- Allievi, A.,Flori, E. (2018, March 01). FinFisher exposed: A researcher’s tale of defeating traps, tricks, and complex virtual machines. Retrieved July 9, 2018.
- Novetta Threat Research Group. (2016, February 24). Operation Blockbuster: Unraveling the Long Thread of the Sony Attack. Retrieved February 25, 2016.
- Novetta Threat Research Group. (2016, February 24). Operation Blockbuster: Destructive Malware Report. Retrieved March 2, 2016.
- Trusted Computing Group. (2008, April 29). Trusted Platform Module (TPM) Summary. Retrieved June 8, 2016.
- Microsoft. (n.d.). Secure the Windows 10 boot process. Retrieved April 23, 2020.