Breaking Secure Bootloaders

This talk outlines weaknesses in modern bootloaders which allow attackers to deploy unsigned code, despite protection mechanisms. The first phase discusses exploitation of bootloaders in modern Android smartphones, demonstrating weaknesses which allow for bypassing bootloader unlocking restrictions, decryption of protected user data, and deployment of malicious software to devices using full disk encryption. The second phase discusses bootloader weaknesses in the secondary hardware used by smartphones, using an embedded RF chip as a target, and demonstrating reverse engineering techniques which identified weaknesses in the signature verification mechanisms of the firmware update protocols used by the bootloader, allowing for deployment of custom firmware to the chip.

• Exploitation of bootloaders in modern Android smartphones
• Weaknesses allowing for bypassing bootloader unlocking restrictions, decryption of protected user data, and deployment of malicious software to devices using full disk encryption
• Bootloader weaknesses in the secondary hardware used by smartphones
• Reverse engineering techniques identifying weaknesses in signature verification mechanisms of firmware update protocols used by bootloader
• Deployment of custom firmware to the chip

The speaker purchased an Android smartphone to do mobile research and realized he needed root access, which required unlocking the bootloader. Some smartphone manufacturers modify the bootloader and add custom functionality which requires custom tools from them in order to unlock their bootloader and other certain features. The speaker analyzed a bootloader unlock and found that during the unlock process, it would send a 256 byte signature which was downloaded from the manufacturer's servers and sent to the phone using a small bit of data that was sent from the phone to the server. This is verified by the bootloader which then unlocked the locking restrictions and allowed rooting of the device as needed.

Bootloaders often use signature verification mechanisms in order to protect a device from executing malicious software. This talk aims to outline actionable weaknesses in modern bootloaders which allow attackers to deploy unsigned code, despite these protection mechanisms. In the first phase of this talk, we will discuss exploitation of the bootloaders in modern Android smartphones, demonstrating weaknesses which allow for bypassing bootloader unlocking restrictions, decryption of protected user data, and deployment of malicious software to devices using full disk encryption. In the second phase, we will discuss bootloader weaknesses in the secondary hardware used by smartphones. Using an embedded RF chip as a target, we will demonstrate reverse engineering techniques which identified weaknesses in the signature verification mechanisms of the firmware update protocols used by the bootloader, allowing for deployment of custom firmware to the chip. REFERENCES: Travis Goodspeed - Great Ideas in Reversing the Tytera MD380: https://nullcon.net/website/archives/ppt/goa-16/Great-Ideas-in-Reversing-the-Tytera-MD380-by-Travis-Goodspeed.pdf Roee Hay - fastboot oem vuln: Android Bootloader Vulnerabilities in Vendor Customizations: https://www.usenix.org/system/files/conference/woot17/woot17-paper-hay.pdf