CVE-2025-9557 is a classic 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 flaw arises from a buffer copy operation that does not verify the size of the input data, leading to an out-of-bound write. This memory corruption can enable an attacker to execute arbitrary code on the affected device or cause a crash resulting in denial of service (DoS). The vulnerability affects all versions of Zephyr, indicating a systemic issue in the codebase. According to the CVSS 3.1 vector (AV:A/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:H), the attack vector is adjacent network, meaning the attacker must have network access close to the device but no privileges or user interaction are required. The impact on confidentiality and integrity is limited to low, but availability impact is high due to potential device crashes. Although no exploits are currently known in the wild, the ease of exploitation and the critical role of Zephyr in embedded environments make this a significant threat. The lack of patch links suggests that fixes may be forthcoming or in progress. The vulnerability can be leveraged to compromise device operation, potentially affecting critical infrastructure or industrial control systems that rely on Zephyr-based devices.

For European organizations, the impact of CVE-2025-9557 is substantial, especially for those deploying Zephyr RTOS in critical embedded systems such as industrial automation, smart city infrastructure, automotive systems, and medical devices. Successful exploitation could lead to arbitrary code execution, allowing attackers to take control of devices, manipulate data, or disrupt operations. Even if code execution is not achieved, forced crashes can cause denial of service, impacting availability of essential services. This is particularly concerning for sectors with stringent uptime requirements like manufacturing, healthcare, and energy. The vulnerability’s network-adjacent attack vector means that internal networks or segmented IoT environments could be targeted by insiders or lateral movement attackers. Given the widespread adoption of Zephyr in European IoT ecosystems, the threat could affect a broad range of devices, increasing the attack surface and potential for cascading failures in interconnected systems.

Organizations should prioritize applying official patches from the Zephyr project as soon as they become available. Until patches are deployed, implement strict input validation and boundary checks at the application layer to prevent malformed data from triggering the overflow. Network segmentation is critical to isolate Zephyr-based devices from untrusted or less secure network segments, reducing the risk of exploitation via adjacent network vectors. Employ intrusion detection systems (IDS) and anomaly detection tools tailored to embedded device traffic to identify suspicious activity indicative of exploitation attempts. Regularly audit and update device firmware and software to minimize exposure. For critical systems, consider deploying runtime protections such as memory protection units (MPUs) or hardware-enforced isolation features to mitigate the impact of buffer overflows. Finally, maintain an inventory of all devices running Zephyr to ensure comprehensive coverage of mitigation efforts.