CVE-2025-9557 is a buffer overflow vulnerability identified in the Zephyr real-time operating system (RTOS), which is widely used in embedded systems and Internet of Things (IoT) devices. The vulnerability stems from a buffer copy operation that fails to verify the size of the input data before copying, resulting in an out-of-bounds write. This classic buffer overflow can corrupt memory adjacent to the buffer, potentially allowing an attacker to execute arbitrary code with the privileges of the affected process. Even on devices equipped with memory protection mechanisms, exploitation can cause crashes leading to denial of service (DoS). The vulnerability affects all versions of Zephyr, indicating a systemic issue in the codebase. The CVSS 3.1 base score is 7.6 (high), with an attack vector of adjacent network (AV:A), low attack complexity (AC:L), no privileges required (PR:N), no user interaction (UI:N), unchanged scope (S:U), and impacts on confidentiality (C:L), integrity (I:L), and high impact on availability (A:H). This means an attacker can exploit the vulnerability remotely within the same network segment without authentication or user action. Although no known exploits are currently reported in the wild, the nature of the vulnerability and its presence in a widely deployed RTOS make it a significant threat. Zephyr’s use in critical embedded applications such as industrial control, automotive systems, and consumer IoT devices amplifies the risk. The lack of available patches at the time of publication necessitates immediate attention to mitigation strategies.

For European organizations, the impact of CVE-2025-9557 can be substantial, especially those relying on Zephyr RTOS in embedded and IoT devices. Exploitation could lead to arbitrary code execution, allowing attackers to take control of devices, manipulate data, or pivot within networks. This is particularly concerning for sectors like manufacturing, automotive, healthcare, and critical infrastructure, where embedded devices play crucial roles. Denial of service caused by crashes can disrupt operations, leading to downtime and potential safety hazards. The confidentiality and integrity impacts, although rated low, still pose risks of data leakage or unauthorized modification. Given the increasing adoption of connected devices in Europe, the vulnerability could facilitate lateral movement or serve as an entry point for broader attacks. The requirement for network adjacency limits remote exploitation but does not eliminate risk in segmented or wireless environments. The absence of known exploits currently provides a window for proactive defense, but the high severity score underscores the urgency of addressing this vulnerability.

1. Monitor Zephyr project communications and apply official patches promptly once released to address CVE-2025-9557. 2. Conduct an inventory of all devices running Zephyr RTOS within the organization to identify potentially vulnerable systems. 3. Implement network segmentation to limit exposure of embedded devices to untrusted networks, reducing the attack surface. 4. Employ strict input validation and boundary checks in custom code interfacing with Zephyr to prevent exploitation of buffer overflows. 5. Utilize hardware memory protection features such as Memory Protection Units (MPUs) and enable stack canaries or similar runtime protections where supported. 6. Regularly update device firmware and maintain secure update mechanisms to facilitate rapid deployment of security fixes. 7. Monitor network traffic for anomalous behavior indicative of exploitation attempts, especially within local network segments. 8. Engage with device vendors and suppliers to ensure they are aware of the vulnerability and have plans to patch affected products. 9. Consider deploying intrusion detection/prevention systems tailored for IoT and embedded environments to detect exploitation attempts. 10. Educate operational technology (OT) and IoT security teams about this vulnerability and best practices for mitigating buffer overflow risks.