CVE-2025-66047 is a critical security vulnerability identified in version 3.9.1 of libbiosig, an open-source library widely used for processing biosignal data such as EEG, ECG, and other physiological signals. The vulnerability is a stack-based buffer overflow (CWE-121) located in the MFER (Medical File Exchange Record) parsing functionality, specifically triggered when processing Tag 131 within an MFER file. This flaw allows an attacker to craft a malicious MFER file that, when parsed by libbiosig, causes a buffer overflow on the stack, potentially overwriting the return address or other control data. This can lead to arbitrary code execution in the context of the vulnerable application without requiring any privileges or user interaction, making it remotely exploitable over networked systems that accept MFER files. The CVSS v3.1 base score of 9.8 reflects the high severity, with metrics indicating network attack vector (AV:N), low attack complexity (AC:L), no privileges required (PR:N), no user interaction (UI:N), and full impact on confidentiality, integrity, and availability (C:H/I:H/A:H). Although no public exploits have been reported yet, the nature of the vulnerability and the widespread use of libbiosig in medical and research environments make it a critical risk. The lack of available patches at the time of disclosure increases the urgency for mitigations. The vulnerability was reserved on 2025-11-21 and published on 2025-12-11, indicating recent discovery and disclosure.

The impact of CVE-2025-66047 on European organizations is significant, particularly for those in healthcare, biomedical research, and industries relying on biosignal processing. Successful exploitation can lead to full system compromise, allowing attackers to execute arbitrary code, steal sensitive patient or research data, disrupt medical devices or research operations, and potentially cause harm to patients if medical devices are involved. The confidentiality of sensitive health data could be breached, integrity of biosignal data corrupted, and availability of critical systems disrupted. Given the critical nature of healthcare infrastructure in Europe and stringent data protection regulations like GDPR, such a breach could result in severe regulatory penalties, reputational damage, and operational downtime. Organizations using libbiosig in medical devices, research labs, or clinical environments are particularly vulnerable. The absence of known exploits currently provides a window for proactive defense, but the ease of exploitation and high severity score indicate a high risk of imminent attacks once exploit code becomes available.

To mitigate CVE-2025-66047, European organizations should immediately identify all systems and applications using libbiosig version 3.9.1, especially those processing MFER files. Since no official patch is available at disclosure, organizations should implement strict input validation and sanitization for MFER files, including rejecting or sandboxing files containing Tag 131 until a patch is released. Employ runtime protections such as stack canaries, address space layout randomization (ASLR), and control flow integrity (CFI) to reduce exploitation risk. Monitor network traffic and file uploads for suspicious MFER files and implement intrusion detection signatures targeting malformed MFER parsing attempts. Coordinate with vendors and open-source maintainers for timely patch releases and apply updates immediately upon availability. Additionally, conduct code audits and penetration testing focused on biosignal processing components. For critical medical devices, consider isolating affected systems from external networks and applying strict access controls. Maintain up-to-date backups and incident response plans tailored to biosignal processing environments.