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 requests that, when executed by an authenticated user’s browser, can upload and install arbitrary firmware onto the device. The consequence is remote code execution (RCE) on the affected microcontroller, enabling full compromise of the device. The vulnerability affects all versions prior to 3.2.1 of the arduino-esp32 core and has been addressed in version 3.2.1. The CVSS 4.0 base score is 8.7, reflecting a high impact due to network attack vector, no privileges or authentication required, but requiring user interaction (UI:P). The vulnerability does not require prior authentication and can be exploited remotely, making it particularly dangerous in environments where devices expose OTA update endpoints over accessible networks. No known exploits are currently reported in the wild, but the ease of exploitation and potential impact warrant immediate attention.

For European organizations, the impact of this vulnerability can be significant, especially for those deploying IoT solutions or embedded systems based on Espressif microcontrollers. Compromise of devices via this vulnerability could lead to unauthorized firmware installation, resulting in device takeover, data exfiltration, disruption of services, or use of compromised devices as footholds for lateral movement within networks. Critical infrastructure sectors such as manufacturing, smart city deployments, utilities, and transportation that utilize ESP32-based devices for control or monitoring could face operational disruptions or safety risks. Additionally, organizations involved in product development or supply chains using arduino-esp32 may suffer intellectual property theft or reputational damage. The vulnerability’s exploitation does not require authentication but does require user interaction, implying that phishing or social engineering could be used to trigger the attack. Given the widespread adoption of ESP32 microcontrollers in Europe for IoT and embedded applications, the threat surface is considerable. The lack of CSRF protection in OTA update mechanisms could also undermine trust in remote device management solutions.

European organizations should prioritize upgrading all affected arduino-esp32 cores to version 3.2.1 or later, where the vulnerability is fixed. In addition, organizations should implement strict network segmentation to isolate IoT devices and restrict access to OTA update endpoints to trusted management networks only. Employing web application firewalls (WAFs) or network intrusion detection systems (NIDS) to monitor and block suspicious POST requests targeting firmware update endpoints can provide additional defense layers. Device manufacturers and integrators should review their firmware update implementations to ensure robust CSRF protections, such as anti-CSRF tokens or same-origin policy enforcement, are in place. User education on phishing and social engineering risks is also critical to reduce the likelihood of user interaction-based exploitation. For devices already deployed, consider disabling OTA update features if not required or implementing authentication and authorization controls around update mechanisms. Regular security audits and penetration testing of IoT device management interfaces can help identify similar weaknesses proactively.