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). 
Adversaries may use bootkits to persist on systems at a layer below the operating system, which may make it difficult to perform full remediation unless an organization suspects one was used and can act accordingly.
Master Boot Record
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. 
Volume Boot Record
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.
|APT28||APT28 has deployed a bootkit along with Downdelph to ensure its persistence on the victim. The bootkit shares code with some variants of BlackEnergy. |
|BOOTRASH||BOOTRASH is a Volume Boot Record (VBR) bootkit that uses the VBR to maintain persistence. |
|FinFisher||Some FinFisher variants incorporate an MBR rootkit.  |
|Lazarus Group||Lazarus Group malware WhiskeyAlfa-Three modifies sector 0 of the Master Boot Record (MBR) to ensure that the malware will persist even if a victim machine shuts down.  |
|ROCKBOOT||ROCKBOOT is a Master Boot Record (MBR) bootkit that uses the MBR to establish persistence. |
|Boot Integrity||Use Trusted Platform Module technology and a secure or trusted boot process to prevent system integrity from being compromised.  |
|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.
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