CVE-2025-54491 is a stack-based buffer overflow vulnerability identified in the MFER parsing functionality of The Biosig Project's libbiosig library, specifically in versions 3.9.0 and the current master branch (commit 35a819fa). The vulnerability arises in biosig.c at line 9191 when processing a patient event tag (0x41) within an MFER file. The code increments a buffer position pointer based on data read from the file without adequate bounds checking, leading to a buffer overflow on the stack. This overflow can be exploited by an attacker supplying a specially crafted MFER file, enabling arbitrary code execution in the context of the vulnerable application. The vulnerability requires no authentication or user interaction and can be triggered remotely if the application processes untrusted MFER files. The CVSS v3.1 score of 9.8 reflects the vulnerability's critical impact on confidentiality, integrity, and availability, with low attack complexity and no privileges required. Although no exploits are currently reported in the wild, the nature of the flaw and its location in a widely used open-source library for biosignal processing make it a high-risk issue. The Biosig Project is used in medical and biometric software to handle physiological data, meaning compromised systems could lead to patient data breaches, system manipulation, or denial of service. The vulnerability is classified under CWE-121 (Stack-based Buffer Overflow), a common and dangerous software weakness that often leads to remote code execution.

For European organizations, particularly those in healthcare, biomedical research, and biometric authentication sectors, this vulnerability poses a significant risk. Exploitation could lead to unauthorized access to sensitive patient data, manipulation of biosignal processing results, or complete system compromise, potentially disrupting critical medical services. The arbitrary code execution capability could allow attackers to implant persistent malware, exfiltrate confidential information, or cause denial of service. Given the reliance on biosignal data for diagnostics and patient monitoring, any compromise could have direct consequences on patient safety and privacy. Additionally, organizations subject to GDPR face legal and financial repercussions if patient data confidentiality is breached. The vulnerability's remote exploitability without authentication increases the attack surface, especially in environments where MFER files are exchanged or processed from external sources. This elevates the urgency for European entities to assess their exposure and implement mitigations promptly.

1. Monitor The Biosig Project repositories and official channels for patches addressing CVE-2025-54491 and apply updates immediately upon release. 2. In the interim, restrict processing of MFER files to trusted and verified sources only, implementing strict input validation and file integrity checks. 3. Employ application-level sandboxing or containerization to limit the impact of potential exploitation within isolated environments. 4. Enable and enforce modern memory protection mechanisms such as stack canaries, ASLR, and DEP/NX on systems running libbiosig to reduce exploitation success. 5. Conduct code audits and fuzz testing on the MFER parsing components to identify and remediate similar vulnerabilities proactively. 6. Implement network-level controls to monitor and block suspicious file transfers or malformed MFER files. 7. Educate developers and system administrators about the risks of processing untrusted biosignal files and enforce secure coding practices. 8. Maintain comprehensive logging and intrusion detection systems to identify exploitation attempts early.