Bootbandit: A macOS Bootloader Attack by Armen Boursalian Full disk encryption (FDE) is used to protect a computer system against data theft by physical access. If a laptop or hard disk drive protected with FDE is stolen or lost, the data remains unreadable without the encryption key. To foil this defense, an intruder can gain physical access to a computer system in a so-called "evil maid" attack, install malware in the boot (pre-operating system) environment, and use the malware to intercept the victim's password. Such an attack relies on the fact that the system is in a vulnerable state before booting into the operating system. In this paper, we discuss an evil maid type of attack, in which the victim's password is stolen in the boot environment, passed to the macOS user environment, and then exfiltrated from the system to the attacker's remote command and control server. On a macOS system, this attack has additional implications due to "password forwarding" technology, in which users' account passwords also serve as FDE passwords. ACKNOWLEDGMENTS First and foremost, I would like to thank Prof. Mark Stamp for his patience and guidance throughout the course of this project. I would also like to thank my team and the leadership at Area 1 Security for supporting my pursuit of the Master of Science degree. v

Historically, the boot phase on personal computers left systems in a relatively vulnerable state. Because traditional antivirus software runs within the operating system, the boot environment is difficult to protect from malware. Examples of attacks against bootloaders include so‐called “evil maid” attacks, in which an intruder physically obtains a boot disk to install malicious software for obtaining the password used to encrypt a disk. The password then must be stored and retrieved again through physical access. In this paper, we discuss an attack that borrows concepts from the evil maid. We assume exploitation can be used to infect a bootloader on a system running macOS remotely to install code to steal the user's password. We explore the ability to create a communication channel between the bootloader and the operating system to remotely steal the password for a disk protected by FileVault 2. On a macOS system, this attack has additional implications due to “password forwarding” technology, in which a user's account password also serves as the FileVault password, enabling an additional attack surface through privilege escalation.