Finding gadgets in incremental code updates for return-oriented programming attacks on resource-constrained devices

Code-reuse attacks pose a threat to embedded devices since they are able to defeat common security defences such as non-executable stacks. To succeed in his code-reuse attack, the attacker has to gain knowledge of some or all of the instructions of the target firmware/software. In case of a bare metal firmware that is protected from being dumped out of a device, it is hard to know the running instructions of the target firmware. This consequently makes code-reuse attacks more difficult to achieve. This paper presents a novel approach how an attacker can gain knowledge of some of these instructions by sniffing unencrypted incremental updates. These updates exist to reduce the radio reception power for resource-constrained devices. It will be demonstrated how a return-oriented programming (ROP) attack can be accomplished on a MSP430 MCU using only the passively sniffed incremental updates. The generated updates of the R3diff and Delta Generator (DG) differencing algorithms will be under assessment. The evaluation reveals that both of them can be exploited by the attacker and how an attacker can maximize his information gain when dealing with more than one update. It also shows that the DG generated updates leak more information than the R3diff generated updates. This stresses the fact that even delta updates need to be protected with encryption. To defend against this attack, different countermeasures that consider different power consumption scenarios are proposed, but yet to be evaluated.