The vulnerability identified as CVE-2025-65821 affects devices running on the ESP32 chip where the UART download mode remains enabled. UART download mode is a hardware feature intended for firmware flashing and debugging during development. When left enabled in production, it allows an adversary with physical access to connect to the device's UART interface and dump the entire flash memory contents. This flash memory includes the Non-Volatile Storage (NVS) partition, which stores sensitive information such as current and previous Wi-Fi network credentials and configuration details. By extracting this data, attackers can gain unauthorized access to network environments or gather intelligence on the device's operational context. Furthermore, the attacker can reflash the device with malicious firmware, effectively taking full control of the device. This can lead to persistent backdoors, data exfiltration, or use of the device as a pivot point within a network. The vulnerability does not require software-level authentication or user interaction, but physical access to the device is mandatory. No CVSS score has been assigned yet, and no public exploits are known at this time. However, the impact on confidentiality, integrity, and availability is significant due to the potential for complete device compromise. The vulnerability primarily affects ESP32-based IoT devices, which are widely used in consumer electronics, industrial control systems, and smart infrastructure.

For European organizations, this vulnerability poses a substantial risk, particularly for sectors relying heavily on IoT devices such as manufacturing, smart cities, utilities, and consumer electronics. Leakage of Wi-Fi credentials can lead to unauthorized network access, enabling lateral movement within corporate or critical infrastructure networks. Reflashing devices with malicious firmware can disrupt operations, cause data breaches, or facilitate espionage. The physical access requirement limits remote exploitation but does not eliminate risk, especially in environments with less stringent physical security or where devices are deployed in public or semi-public spaces. The compromise of ESP32 devices could undermine trust in IoT deployments and cause regulatory compliance issues under GDPR if personal data is exposed. Additionally, supply chain risks arise if devices are tampered with before deployment. The absence of known exploits suggests a window for proactive mitigation before widespread attacks occur.

To mitigate this vulnerability, organizations should ensure that UART download mode is disabled on all ESP32 devices before deployment. This can be achieved by configuring the chip's eFuse settings to disable UART bootloader functionality permanently. Implementing secure boot mechanisms will prevent unauthorized firmware from running on the device, while enabling flash encryption protects stored data from being read even if the flash is dumped. Physical security controls must be enhanced to restrict unauthorized access to devices, especially in public or unmonitored locations. Regular firmware integrity checks and monitoring for anomalous device behavior can help detect compromise. Vendors should provide updated firmware and guidance to customers, and organizations should audit their device inventories to identify affected ESP32-based products. For new deployments, consider alternative hardware platforms with stronger security defaults. Finally, educating staff on the risks of physical device tampering is essential.