FirmEM: Firmware Flashing Detection via Unintentional Electromagnetic Emissions

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Ensuring the integrity of firmware running on embedded systems—such as automotive Electronic Control Units (ECUs)—is critical to system reliability and security. This paper presents a lightweight, non-intrusive method for detecting firmware flashing events using electromagnetic (EM) sidechannel emissions collected via low-cost software-defined radios (SDRs). By focusing on short, deterministic update phases (e.g., bootloader-based flashing), we avoid the overhead of continuous monitoring. We propose a kernel-based pattern matching framework that identifies flashing operations by comparing short-time spectral signatures to a reference. We validate this approach on SAMV71 development boards and show that appropriate frequency band selection is key to signal clarity. Cross-board experiments reveal challenges related to hardware variability, including missing components. These results highlight the feasibility of EM-based firmware inspection in real-world, resource-constrained environments.