Researchers Demonstrate Qualcomm Boot ROM Exploit via Sahara USB Protocol

Summary

Researchers demonstrate a Qualcomm boot ROM flaw that uses repeated Sahara USB commands to gain privileged code execution and root a Pixel 3. They describe exploit development and mitigations in newer chipsets.

Key points

• A Sahara state-machine reset command can repeatedly add stack frames without returning, eventually overwriting other data in limited boot ROM memory.
• On the SDM 845, the researchers used certificate parsing to overwrite a cryptographic function pointer and gain control of execution.
• Their exploit used a return-oriented programming chain to disable memory protections and load a larger payload over USB.
• A live demonstration used emergency download mode on a Pixel 3 and modified the boot process to obtain root access.
• The researchers said production Snapdragon 865 devices generally received a fuse-based mitigation, while a later chipset fixed the flaw in ROM.
• Newer chipsets use a separate trust management engine for authentication, making application boot ROM execution alone insufficient to control the entire boot process.