Is the Canary Dead? On the Effectiveness of Stack Canaries on Microcontroller Systems

Microcontroller units (MCUs) are compact computers tailored for embedded and Internet-of-Things (IoT) applications. MCU-based devices primarily run software systems coded in low-level languages such as C, making them susceptible to memory corruption attacks like stack-based buffer overflows. Stack canaries are a low-overhead buffer overflow detection mechanism that offers a certain level of protection and is frequently used in microprocessor systems in both the kernel and application layers. However, their effectiveness and overhead on microcontroller systems have not been extensively studied. As a result, the community naively assumes that the stack canary mechanism on microcontrollers provides the same level of security as it does on microprocessor systems.In this paper, we present a study that centers on the implementation and utilization of stack canaries in microcontroller systems. More specifically, we delve into the support for stack canaries across libraries, compilers, and system layers. Our findings suggest that the implementations of stack canaries on microcontroller systems are generally less secure than their counterparts on microprocessors. Additionally, we conducted measurements to assess the overhead of stack canaries within Zephyr, a popular real-time operating system for microcontrollers. We aim for this paper to illustrate the limitations of stack canaries on microcontrollers and advocate for the exploration of alternative solutions.