Abstract-To address the growing concerns about the security of embedded systems, it is important to perform accurate analysis of firmware binaries, even when the source code or the hardware documentation are not available. However, research in this field is hindered by the lack of dedicated tools. For example, dynamic analysis is one of the main foundations of security analysis, e.g., through dynamic taint tracing or symbolic execution. Unlike static analysis, dynamic analysis relies on the ability to execute software in a controlled environment, often an instrumented emulator. However, emulating firmwares of embedded devices requires accurate models of all hardware components used by the system under analysis. Unfortunately, the lack of documentation and the large variety of hardware on the market make this approach infeasible in practice.In this paper we present Avatar, a framework that enables complex dynamic analysis of embedded devices by orchestrating the execution of an emulator together with the real hardware. We first introduce the basic mechanism to forward I/O accesses from the emulator to the embedded device, and then describe several techniques to improve the system's performance by dynamically optimizing the distribution of code and data between the two environments. Finally, we evaluate our tool by applying it to three different security scenarios, including reverse engineering, vulnerability discovery and hardcoded backdoor detection. To show the flexibility of Avatar, we perform this analysis on three completely different devices: a GSM feature phone, a hard disk bootloader, and a wireless sensor node.

Device attestation is an essential feature in many security protocols and applications. The lack of dedicated hardware and the impossibility to physically access devices to be attested, makes attestation of embedded devices, in applications such as Wireless Sensor Networks, a prominent challenge. Several software-based attestation techniques have been proposed that either rely on tight time constraints or on the lack of free space to store malicious code. This paper investigates the shortcomings of existing software-based attestation techniques. We first present two generic attacks, one based on a return-oriented rootkit and the other on code compression. We further describe specific attacks on two existing proposals, namely SWATT and ICE-based schemes, and argue about the difficulty of fixing them. All attacks presented in this paper were implemented and validated on commodity sensors.

Harvard architecture CPU design is common in the embedded world. Examples of Harvard-based architecture devices are the Mica family of wireless sensors. Mica motes have limited memory and can process only very small packets. Stack-based buffer overflow techniques that inject code into the stack and then execute it are therefore not applicable. It has been a common belief that code injection is impossible on Harvard architectures. This paper presents a remote code injection attack for Mica sensors. We show how to exploit program vulnerabilities to permanently inject any piece of code into the program memory of an Atmel AVR-based sensor. To our knowledge, this is the first result that presents a code injection technique for such devices. Previous work only succeeded in injecting data or performing transient attacks. Injecting permanent code is more powerful since the attacker can gain full control of the target sensor. We also show that this attack can be used to inject a worm that can propagate through the wireless sensor network and possibly create a sensor botnet. Our attack combines different techniques such as return oriented programming and fake stack injection. We present implementation details and suggest some counter-measures.