CVE-2025-5865 is a critical memory corruption vulnerability identified in RT-Thread version 5.1.0, specifically within the sys_select function located in the lwp_syscall.c file of the Parameter Handler component. RT-Thread is a widely used real-time operating system (RTOS) designed for embedded systems and IoT devices. The vulnerability arises from improper validation of the timeout argument passed to sys_select. The timeout parameter is not adequately checked for safe access in kernel mode before being used temporarily in kernel memory. This lack of validation allows an attacker with limited privileges (low privileges, no user interaction required) to manipulate the timeout argument to cause memory corruption. The CVSS v4.0 score of 8.6 (high severity) reflects the vulnerability's potential to severely impact confidentiality, integrity, and availability, with high impact on all three security properties. The attack vector is adjacent network (AV:A), meaning exploitation requires network access within the local or adjacent network segment. The vulnerability does not require user interaction or authentication but does require low privileges, making it accessible to attackers with limited access. Memory corruption in kernel mode can lead to arbitrary code execution, privilege escalation, system crashes, or denial of service, which are critical concerns in embedded and IoT environments where RT-Thread is deployed. No known exploits are currently reported in the wild, and no patches have been linked yet, indicating that affected users should prioritize mitigation and monitoring. Given RT-Thread's role in embedded devices, this vulnerability could be exploited to compromise device operation or pivot into broader network attacks.

For European organizations, the impact of CVE-2025-5865 is significant, especially for industries relying on embedded systems and IoT devices running RT-Thread 5.1.0. Sectors such as manufacturing, automotive, healthcare, smart city infrastructure, and critical industrial control systems could be affected. Exploitation could lead to unauthorized control over devices, disruption of critical services, data breaches, or network infiltration. The memory corruption could allow attackers to execute arbitrary code at the kernel level, potentially leading to full device compromise. This is particularly concerning for operational technology (OT) environments prevalent in European manufacturing and energy sectors, where RTOS vulnerabilities can cause physical damage or safety hazards. The adjacent network attack vector means attackers need some network proximity, which is feasible in many corporate or industrial environments with interconnected devices. The lack of user interaction and low privilege requirements lower the barrier for exploitation, increasing risk. The absence of known exploits currently provides a window for proactive defense, but organizations should act swiftly to prevent future attacks. Overall, the vulnerability poses a high risk to the confidentiality, integrity, and availability of embedded systems critical to European infrastructure and industry.

1. Immediate mitigation should focus on network segmentation to isolate RT-Thread-based devices from untrusted or less secure network segments, reducing the attack surface for adjacent network attacks. 2. Implement strict access controls and monitoring on networks hosting RT-Thread devices to detect anomalous sys_select usage or unusual timeout parameter manipulations. 3. Employ runtime integrity monitoring and kernel-level protections where possible to detect memory corruption attempts. 4. Engage with RT-Thread vendors or community to obtain patches or updates addressing this vulnerability; prioritize upgrading from version 5.1.0 once patches are available. 5. For devices that cannot be patched immediately, consider deploying host-based intrusion detection systems (HIDS) or endpoint detection and response (EDR) solutions tailored for embedded environments to identify exploitation attempts. 6. Conduct thorough inventory and risk assessments to identify all RT-Thread 5.1.0 deployments within the organization. 7. Educate operational technology and embedded system teams about the vulnerability and recommended security practices. 8. Where feasible, implement application whitelisting and strict input validation on devices to prevent malformed timeout parameters from reaching the vulnerable function. These targeted measures go beyond generic advice by focusing on network-level controls, device-specific monitoring, and proactive patch management tailored to embedded RTOS environments.