CVE-2025-53511: 
Linux Debian vulnerability analysis and mitigation

CVE-2025-53511 is a heap-based buffer overflow vulnerability in the MFER (Medical waveform Format Encoding Rules) parsing functionality of The Biosig Project libbiosig. A specially crafted MFER file can trigger the overflow, potentially leading to arbitrary code execution. Affected versions include libbiosig 3.9.0 and the Master Branch at commit 35a819fa. The vulnerability was disclosed to the vendor on 2025-08-06, patched on 2025-08-24, and publicly released on 2025-08-25. It carries a CVSS v3.1 base score of 9.8 (Critical) (Talos Advisory).

The root cause (CWE-122: Heap-based Buffer Overflow) lies in a mismatch between the initial heap allocation size of the hdr->CHANNEL array and the default value of hdr->NS in the MFER processing code within sopen_extended() in biosig.c. When constructHDR(0, 0) is called, hdr->CHANNEL is allocated via calloc(0, sizeof(CHANNEL_TYPE)), resulting in a minimal allocation (effectively 16 usable bytes on x86-64 Linux). However, the MFER processing block hardcodes hdr->NS = 1 as the default channel count, and if no tag-5 frame (which triggers a realloc to resize hdr->CHANNEL) is present in the file, the post-parse channel processing loop iterates once over the undersized buffer. Nearly every write in this loop — including writes to Transducer[0] (offset 152 bytes) and SPR (partially attacker-controlled via tag-4 frame data) — overflows the heap allocation. The attack vector is a malicious MFER file supplied to any application using libbiosig for file parsing; no authentication or user interaction beyond file processing is required (Talos Advisory).

Successful exploitation can result in full compromise of confidentiality, integrity, and availability on the affected system. Because some overflow writes use attacker-controlled data (e.g., the hdr->SPR value set via a tag-4 frame), an attacker can potentially achieve arbitrary code execution with the privileges of the process loading the malicious MFER file. Applications built on libbiosig — including biosig APIs for Octave and MATLAB, sigviewer, and other biomedical signal processing tools — are all at risk, potentially exposing sensitive medical signal data and enabling lateral movement within clinical or research environments (Talos Advisory).

1. Craft a malicious MFER file: Create a file beginning with the magic bytes @ MFER (8 bytes) or @ MFR (6 bytes) to pass libbiosig's file type detection in getfiletype().
2. Omit the tag-5 (channel count) frame: Do not include a TLV frame with tag=5 in the file. This ensures hdr->NS remains at its default value of 1 and hdr->CHANNEL is never resized via realloc, leaving it at its minimal initial allocation.
3. Optionally include a tag-4 (SPR) frame: Insert a TLV frame with tag=4 containing an attacker-controlled value. This sets hdr->SPR to an arbitrary value, which will later be written out-of-bounds into the heap during channel processing, providing partial write-what-where control.
4. Deliver the file to a vulnerable application: Supply the crafted MFER file to any application that uses libbiosig for parsing (e.g., sigviewer, a MATLAB/Octave biosig script, or a custom tool calling sopen_extended()).
5. Trigger the overflow: When sopen_extended() processes the file, the post-parse channel loop iterates once (k=0 to hdr->NS=1) and writes to hdr->CHANNEL[0] members at offsets well beyond the 16-byte allocation, causing a heap-based buffer overflow. Depending on heap layout, this can be leveraged for arbitrary code execution (Talos Advisory).

• File System: Presence of unexpected or externally sourced .mfer or .mfr files in directories processed by libbiosig-based applications; files beginning with magic bytes @ MFER or @ MFR that lack a tag-5 channel count frame.
• Process: Crashes or abnormal termination of applications using libbiosig (e.g., sigviewer, MATLAB/Octave biosig scripts) when processing MFER files; AddressSanitizer output referencing sopen_extended in biosig.c:9252 if instrumented builds are in use.
• Logs: Application crash logs or core dumps referencing sopen_extended, constructHDR, or heap corruption errors; error messages such as Warning MFER tag0 incorrect length or similar MFER parsing warnings without a corresponding tag-5 frame log entry.
• Network: Unexpected inbound file transfers (e.g., via web upload, email attachment, or shared storage) of MFER-format files to systems running libbiosig-based software.

The vendor released a patch on 2025-08-24; users should upgrade libbiosig to a version beyond the Master Branch commit 35a819fa or beyond version 3.9.0 that incorporates the fix. As a workaround where patching is not immediately possible, disable MFER file processing, implement strict allowlisting of file sources, and use network segmentation to limit exposure of systems running libbiosig-based applications. Monitoring and restricting file uploads from untrusted sources is also recommended (Talos Advisory).

Cisco Talos researchers Mark Bereza and Lilith discovered and reported the vulnerability, with Talos publishing a detailed technical advisory (TALOS-2025-2237) on 2025-08-25 that includes a proof-of-concept file and full root cause analysis. The vulnerability was also covered in a Talos blog post grouping it with other vulnerabilities in libbiosig, Tenda, SAIL, PDF-XChange, and Foxit products (Talos Blog). Community aggregators including malware.news and vulnerability tracking platforms (VulDB, CVEfeed, CIRCL) indexed the advisory shortly after public release, indicating moderate security community awareness.