AVRAND: A Software-Based Defense Against Code Reuse Attacks for AVR Embedded Devices

Code reuse attacks are advanced exploitation techniques that constitute a serious threat for modern systems. They profit from a control flow hijacking vulnerability to maliciously execute one or more pieces of code from the targeted application. ASLR and Control Flow Integrity are two mechanisms commonly used to deter automated attacks based on code reuse. Unfortunately, none of these solutions are suitable for modified Harvard architectures such as AVR microcontrollers. In this work, we present a code reuse attack against embedded AVR devices that shows how an adversary can execute arbitrary code reused from the firmware and other external libraries. We then propose a software-based defense based on fine-grained random permutations of the code memory. Our solution is installed in the bootloader section of the embedded device and thus executes during every device reset. We also propose a self-obfuscation technique to hinder code-reuse attacks against the bootloader.