A stack-based buffer overflow vulnerability exists in the MFER parsing functionality of The Biosig Project libbiosig 3.9.0 and Master Branch (35a819fa). A specially crafted MFER file can lead to arbitrary code execution. An attacker can provide a malicious file to trigger this vulnerability.This vulnerability manifests on line 8970 of biosig.c on the current master branch (35a819fa), when the Tag is 63:

            else if (tag==63) {
                uint8_t tag2=255, len2=255;

                count = 0;
                while ((count<len) && !(FlagInfiniteLength && len2==0 && tag2==0)){
                    curPos += ifread(&tag2,1,1,hdr);
                    curPos += ifread(&len2,1,1,hdr);
                    if (VERBOSE_LEVEL==9)
                        fprintf(stdout,"MFER: tag=%3i chan=%2i len=%-4i tag2=%3i len2=%3i curPos=%i %li count=%4i\n",tag,chan,len,tag2,len2,curPos,iftell(hdr),(int)count);

                    if (FlagInfiniteLength && len2==0 && tag2==0) break;

                    count  += (2+len2);
                    curPos += ifread(&buf,1,len2,hdr);

Here, the number of bytes read is not the Data Length decoded from the current frame in the file (len) but rather is a new length contained in a single octet read from the same input file (len2). Despite this, a stack-based buffer overflow condition can still occur, as the destination buffer is still buf, which has a size of only 128 bytes, while len2 can be as large as 255.

References

• https://nvd.nist.gov/vuln/detail/CVE-2025-54489
• https://talosintelligence.com/vulnerability_reports/TALOS-2025-2234