CVE-2025-53540 is a high-severity vulnerability affecting the arduino-esp32 core, which supports multiple Espressif microcontrollers including ESP32, ESP32-S2, ESP32-S3, ESP32-C3, ESP32-C6, and ESP32-H2. The vulnerability arises from a lack of Cross-Site Request Forgery (CSRF) protection in several Over-The-Air (OTA) update examples and the HTTPUpdateServer implementation. Specifically, the firmware update endpoints accept POST requests for firmware uploads without verifying the legitimacy of the request origin. This flaw allows an attacker to craft malicious web pages or requests that, when visited or triggered by an authenticated user, can cause the device to accept and install arbitrary firmware. The consequence is remote code execution (RCE) on the affected device, enabling full control over the microcontroller. The vulnerability affects all versions prior to 3.2.1 of arduino-esp32 and has been fixed in version 3.2.1. The CVSS 4.0 base score is 8.7, reflecting a network attack vector, low attack complexity, no privileges or user interaction required, and high impact on confidentiality, integrity, and availability. No known exploits are currently reported in the wild. This vulnerability is particularly critical because ESP32-based devices are widely used in IoT applications, embedded systems, and industrial controls, where unauthorized firmware modification can lead to device compromise, data leakage, or disruption of service.

For European organizations, the impact of this vulnerability can be significant, especially for those deploying ESP32-based devices in critical infrastructure, industrial automation, smart building systems, or consumer IoT products. Successful exploitation could lead to unauthorized remote control of devices, data exfiltration, sabotage, or pivoting into internal networks. Given the widespread adoption of ESP32 microcontrollers in Europe’s growing IoT ecosystem, including smart city deployments and manufacturing automation, the risk extends to operational disruptions and potential safety hazards. Confidentiality breaches could expose sensitive operational data, while integrity violations could result in malicious firmware altering device behavior. Availability impacts could cause denial of service or device bricking. The lack of required authentication or user interaction for exploitation increases the threat level, making it easier for attackers to compromise devices remotely. This vulnerability could also be leveraged in supply chain attacks or targeted espionage campaigns against European technology firms using these microcontrollers.

European organizations should immediately upgrade all arduino-esp32 cores to version 3.2.1 or later to apply the official fix. For devices already deployed, implement network-level protections such as firewall rules to restrict access to OTA update endpoints only to trusted management networks. Employ network segmentation to isolate IoT devices from critical infrastructure and sensitive data environments. Where possible, disable OTA update functionality if not required or restrict it to authenticated and encrypted channels (e.g., HTTPS with mutual TLS). Conduct thorough firmware integrity verification using cryptographic signatures before applying updates. Monitor network traffic for unusual POST requests targeting update endpoints and implement anomaly detection to identify potential exploitation attempts. Additionally, educate developers and system integrators about secure coding practices to avoid CSRF vulnerabilities and ensure that all web interfaces handling firmware updates include robust anti-CSRF tokens or equivalent protections. Regularly audit and inventory ESP32-based devices to ensure timely patching and compliance.