CVE-2025-9558 identifies a classic buffer overflow vulnerability in the Zephyr real-time operating system, specifically within the gen_prov_start function in the pb_adv.c source file. The vulnerability occurs because the function copies the entire length of received data into the link.rx.buf buffer without validating whether the input size fits within the buffer's allocated memory. This unchecked copy operation leads to an out-of-bounds write condition, which can corrupt adjacent memory regions. Such memory corruption can cause unpredictable behavior including crashes, denial of service, or potentially arbitrary code execution if exploited skillfully. The vulnerability affects all versions of Zephyr, indicating a systemic issue in the codebase. The CVSS v3.1 score of 7.6 reflects a high severity rating, with an attack vector over the network (AV:A), low attack complexity (AC:L), no privileges required (PR:N), and no user interaction needed (UI:N). The impact scope is unchanged (S:U), with low confidentiality and integrity impact but high availability impact, meaning the primary risk is service disruption. No known exploits are currently in the wild, but the vulnerability's nature and ease of exploitation suggest it could be targeted in the future. Zephyr is widely used in embedded systems and IoT devices, which often operate in critical infrastructure and industrial environments, increasing the potential impact of this vulnerability.

For European organizations, the vulnerability poses significant risks especially in sectors relying on embedded and IoT devices running Zephyr RTOS, such as manufacturing, automotive, smart cities, and critical infrastructure. Exploitation could lead to denial of service conditions, disrupting operational technology systems and causing downtime or safety hazards. Memory corruption could also be leveraged to escalate attacks, potentially compromising device integrity or leaking sensitive data. Given the network attack vector and no requirement for authentication, attackers could remotely exploit vulnerable devices if exposed to untrusted networks. This is particularly concerning for devices deployed in distributed environments or connected to public or semi-public networks. The impact on availability is high, which could affect service continuity and operational reliability. Confidentiality and integrity impacts are rated low but cannot be dismissed, especially if combined with other vulnerabilities. The widespread use of Zephyr in European industrial and consumer IoT markets means the threat could affect a broad range of devices and systems.

European organizations should implement a multi-layered mitigation strategy. First, monitor Zephyr project communications and apply official patches promptly once released to address CVE-2025-9558. Until patches are available, consider deploying network-level controls such as segmentation and firewall rules to restrict access to devices running Zephyr, especially blocking untrusted or external network traffic to vulnerable services. Conduct thorough code audits and static analysis on custom Zephyr-based firmware to identify and remediate unsafe buffer handling. Employ runtime protections like stack canaries, address space layout randomization (ASLR), and memory protection units (MPUs) where supported by hardware to reduce exploitation success. Implement strict input validation and size checks in any custom code interfacing with the affected functions. Regularly perform vulnerability scanning and penetration testing focused on embedded devices to detect exploitation attempts. Finally, maintain an inventory of all Zephyr-based devices in the environment to prioritize risk management and incident response planning.