CVE-2025-54481 is a critical stack-based buffer overflow vulnerability identified in The Biosig Project's libbiosig library, specifically affecting versions 3.9.0 and the current master branch (commit 35a819fa). The vulnerability arises in the MFER (Medical Format for Electroencephalographic Recordings) parsing functionality, where a specially crafted MFER file can trigger a buffer overflow leading to arbitrary code execution. The root cause is located in biosig.c at line 8744, where a fixed-size character array 'v' of 17 bytes is used to store data read from the file. The code reads 'len' bytes into 'v' without adequately ensuring that 'len' does not exceed the buffer size. Although there is a warning if 'len' is greater than 16, the code proceeds to read and then null-terminate the buffer at v[len], which can overflow the buffer if 'len' is larger than 16. This overflow allows an attacker to overwrite adjacent stack memory, potentially leading to control flow hijacking and arbitrary code execution. The vulnerability requires no authentication or user interaction, and the attack vector is a malicious MFER file processed by libbiosig. Given the CVSS 3.1 base score of 9.8 (AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H), this vulnerability is highly exploitable remotely and can severely compromise confidentiality, integrity, and availability of affected systems. No known exploits are reported in the wild yet, but the critical nature and ease of exploitation make it a significant threat to any system using libbiosig for MFER file processing.

For European organizations, the impact of this vulnerability can be substantial, especially those involved in medical research, healthcare, and biomedical engineering where libbiosig is used to process EEG and other biosignal data in MFER format. Exploitation could allow attackers to execute arbitrary code on systems handling sensitive medical data, leading to data breaches, manipulation of medical records, or disruption of critical healthcare services. This could result in violation of GDPR regulations due to unauthorized access to personal health information, causing legal and financial repercussions. Additionally, compromised systems could be leveraged as footholds for lateral movement within networks, threatening broader organizational infrastructure. The critical severity and remote exploitability mean that even perimeter defenses may be bypassed if malicious MFER files are accepted from external sources or untrusted users. The lack of authentication or user interaction requirements further increases risk, as automated processing pipelines could be targeted without direct user involvement.

Organizations should immediately audit their use of libbiosig, particularly versions 3.9.0 and the specified master branch, to identify affected systems. Since no official patches are currently available, temporary mitigations include: 1) Implement strict input validation and sanitization on MFER files before processing, rejecting files with suspiciously large tag lengths or malformed structures. 2) Employ sandboxing or containerization to isolate the libbiosig processing environment, limiting potential damage from exploitation. 3) Monitor and restrict sources of MFER files, ensuring only trusted and verified inputs are processed. 4) Use compiler and OS-level security features such as stack canaries, ASLR (Address Space Layout Randomization), and DEP (Data Execution Prevention) to mitigate exploitation impact. 5) Engage with The Biosig Project or maintainers to track patch releases and apply updates promptly once available. 6) Conduct internal security testing and fuzzing on MFER parsing to detect similar vulnerabilities proactively. 7) Educate relevant staff about the risks of processing untrusted biosignal files and enforce strict operational security policies around file handling.