CVE-2025-69209 is a classic stack-based buffer overflow vulnerability identified in the ArduinoCore-avr platform, specifically affecting versions prior to 1.8.7. ArduinoCore-avr provides the source code and configuration files for Arduino AVR Boards, widely used in embedded and IoT devices. The vulnerability arises in the dtostrf function, which converts floating-point values to strings. When an attacker supplies an excessively large decimalPlaces parameter to String constructors or concat methods that internally call dtostrf, the function writes beyond the bounds of fixed-size stack buffers. This unchecked buffer copy leads to memory corruption, which can cause denial of service by crashing the device. More critically, under certain conditions, it can enable arbitrary code execution on the AVR microcontroller, potentially allowing an attacker to take control of the device. The vulnerability does not require authentication or user interaction but does require local code execution capability to trigger. The Arduino team addressed this issue in version 1.8.7 by adding proper bounds checking to prevent buffer overflow. No known exploits are currently in the wild, but the vulnerability poses a risk to embedded systems relying on vulnerable Arduino AVR boards, especially in industrial or critical infrastructure contexts.

For European organizations, the impact of CVE-2025-69209 can be significant, particularly for those deploying Arduino AVR-based devices in industrial automation, manufacturing, smart city infrastructure, or IoT applications. Exploitation could lead to device crashes causing denial of service, disrupting operational technology systems. In worst-case scenarios, attackers could achieve arbitrary code execution, potentially allowing them to manipulate device behavior, exfiltrate sensitive data, or pivot into broader network environments. This risk is heightened in sectors such as automotive manufacturing, energy, and critical infrastructure where Arduino AVR boards may be embedded in control systems. The vulnerability's local exploit requirement limits remote attacks but insider threats or supply chain compromises could leverage it. Disruption or compromise of embedded devices could result in operational downtime, safety hazards, and financial losses. Given the widespread use of Arduino platforms in prototyping and production, organizations must assess their exposure carefully.

European organizations should immediately verify if they use ArduinoCore-avr versions earlier than 1.8.7 in any embedded or IoT devices. The primary mitigation is to upgrade all affected Arduino AVR boards and development environments to version 1.8.7 or later, which contains the patch preventing buffer overflow. Additionally, organizations should audit all code that performs floating-point to string conversions with high precision to ensure no unsafe parameters are passed. Implementing strict input validation and limiting decimalPlaces values can reduce risk. For deployed devices where firmware updates are challenging, consider isolating vulnerable devices on segmented networks to limit potential impact. Monitoring device logs for crashes or anomalous behavior may help detect exploitation attempts. Finally, incorporate secure coding practices and regular vulnerability assessments in embedded device development lifecycles to prevent similar issues.