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1. IoT Firmware Emulation and Its Security Application in Fuzzing: A Critical Revisit

   https://doi.org/10.3390/fi17010019  

   Zhou, Wei; Shen, Shandian; Liu, Peng (January 2025, Future Internet)

   As IoT devices with microcontroller (MCU)-based firmware become more common in our lives, memory corruption vulnerabilities in their firmware are increasingly targeted by adversaries. Fuzzing is a powerful method for detecting these vulnerabilities, but it poses unique challenges when applied to IoT devices. Direct fuzzing on these devices is inefficient, and recent efforts have shifted towards creating emulation environments for dynamic firmware testing. However, unlike traditional software, firmware interactions with peripherals that are significantly more diverse presents new challenges for achieving scalable full-system emulation and effective fuzzing. This paper reviews 27 state-of-the-art works in MCU-based firmware emulation and its applications in fuzzing. Instead of classifying existing techniques based on their capabilities and features, we first identify the fundamental challenges faced by firmware emulation and fuzzing. We then revisit recent studies, organizing them according to the specific challenges they address, and discussing how each specific challenge is addressed. We compare the emulation fidelity and bug detection capabilities of various techniques to clearly demonstrate their strengths and weaknesses, aiding users in selecting or combining tools to meet their needs. Finally, we highlight the remaining technical gaps and point out important future research directions in firmware emulation and fuzzing. 

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2. On Runtime Software Security of TrustZone-M Based IoT Devices

   https://doi.org/10.1109/GLOBECOM42002.2020.9322370  

   Luo, Lan; Zhang, Yue; Zou, Cliff; Shao, Xinhui; Ling, Zhen; Fu, Xinwen (December 2020, GLOBECOM 2020 - 2020 IEEE Global Communications Conference)

   null (Ed.)

   Internet of Things (IoT) devices have been increasingly integrated into our daily life. However, such smart devices suffer a broad attack surface. Particularly, attacks targeting the device software at runtime are challenging to defend against if IoT devices use resource-constrained microcontrollers (MCUs). TrustZone-M, a TrustZone extension for MCUs, is an emerging security technique fortifying MCU based IoT devices. This paper presents the first security analysis of potential software security issues in TrustZone-M enabled MCUs. We explore the stack-based buffer overflow (BOF) attack for code injection, return-oriented programming (ROP) attack, heap-based BOF attack, format string attack, and attacks against Non-secure Callable (NSC) functions in the context of TrustZone-M. We validate these attacks using the Microchip SAM L11 MCU, which uses the ARM Cortex-M23 processor with the TrustZone-M technology. Strategies to mitigate these software attacks are also discussed. 

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3. SIC ² : Securing Microcontroller Based IoT Devices with Low-cost Crypto Coprocessors

   https://doi.org/10.1109/ICPADS51040.2020.00057  

   Pearson, Bryan; Zou, Cliff; Zhang, Yue; Ling, Zhen; Fu, Xinwen (December 2020, 2020 IEEE 26th International Conference on Parallel and Distributed Systems (ICPADS))

   null (Ed.)

   In this paper, we explore the use of microcontrollers (MCUs) and crypto coprocessors to secure IoT applications, and show how developers may implement a low-cost platform that provides protects private keys against software attacks. We first demonstrate the plausibility of format string attacks on the ESP32, a popular MCU from Espressif that uses the Harvard architecture. The format string attacks can be used to remotely steal private keys hard-coded in the firmware. We then present a framework termed SIC 2 (Securing IoT with Crypto Coprocessors), for secure key provisioning that protects end users' private keys from both software attacks and untrustworthy manufacturers. As a proof of concept, we pair the ESP32 with the low-cost ATECC608A cryptographic coprocessor by Microchip and connect to Amazon Web Services (AWS) and Amazon Elastic Container Service (EC2) using a hardware-protected private key, which provides the security features of TLS communication including authentication, encryption and integrity. We have developed a prototype and performed extensive experiments to show that the ATECC608A crypto chip may significantly reduce the TLS handshake time by as much as 82% with the remote server, and it may lower the total energy consumption of the system by up to 70%. Our results indicate that securing IoT with crypto coprocessors is a practicable solution for low-cost MCU based IoT devices. 

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4. FirmXRay: Detecting Bluetooth Link Layer Vulnerabilities From Bare-Metal Firmware

   https://doi.org/10.1145/3372297.3423344  

   Wen, Haohuang; Lin, Zhiqiang; Zhang, Yinqian (January 2020, ACM SIGSAC Conference on Computer and Communications Security)

   null (Ed.)

   Today, Bluetooth 4.0, also known as Bluetooth Low Energy (BLE), has been widely used in many IoT devices (e.g., smart locks, smart sensors, and wearables). However, BLE devices could contain a number of vulnerabilities at the BLE link layer during broadcasting, pairing, and message transmission. To detect these vulnerabilities directly from the bare-metal firmware, we present FirmXRay, the first static binary analysis tool with a set of enabling techniques including a novel base address identification algorithm for robust firmware disassembling, precise data structure recognition, and configuration value resolution. As a proof-of-concept, we focus on the BLE firmware from two leading SoC vendors (i.e., Nordic and Texas Instruments), and implement a prototype of FirmXRay atop Ghidra. We have evaluated FirmXRay with 793 unique firmware (corresponding to 538 unique devices) collected using a mobile app based approach, and our experiment results show that 98.1% of the devices have configured random static MAC addresses, 71.5% Just Works pairing, and 98.5% insecure key exchanges. With these vulnerabilities, we demonstrate identity tracking, spoofing, and eavesdropping attacks on real-world BLE devices. 

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5. Capture: Centralized Library Management for Heterogeneous IoT Devices

   Zhang, H; Anilkumar, A; Fredrikson, M; Agarwal, Y (August 2021, 30th USENIX Security Symposium (USENIX Security 21))

   With their growing popularity, Internet-of-Things (IoT) devices have become attractive targets for attack. Like most modern software systems, IoT device firmware depends on external third-party libraries extensively, increasing the attack surface of IoT devices. Furthermore, we find that the risk is compounded by inconsistent library management practices and delays in applying security updates—sometimes hundreds of days behind the public availability of critical patches—by device vendors. Worse yet, because these dependencies are "baked into" the vendor-controlled firmware, even security-conscious users are unable to take matters into their own hands when it comes to good security hygiene. We present Capture, a novel architecture for deploying IoT device firmware that addresses this problem by allowing devices on a local network to leverage a centralized hub with third-party libraries that are managed and kept up-to-date by a single trusted entity. An IoT device supporting Capture comprises of two components: Capture-enabled firmware on the device and a remote driver that uses third-party libraries on the Capture hub in the local network. To ensure isolation, we introduce a novel Virtual Device Entity (VDE) interface that facilitates access control between mutually-distrustful devices that reside on the same hub. Our evaluation on a prototype implementation of Capture, along with 9 devices and 3 automation applets ported to our framework, shows that our approach incurs low overhead in most cases (<15% increased latency, <10% additional resources). We show that a single Capture Hub with modest hardware can support hundreds of devices, keeping their shared libraries up-to-date. 

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