External risk intelligence

Libbiosig MFER Parsing Stack Buffer Overflow Arbitrary Code Execution

CVE advisorySeverity: CRITICAL (CVSS 9.8)

CVE-2025-66043

libbiosig is a library used for processing biomedical signal data files. It is not an internet-facing service, web application, or edge gateway. The vulnerability requires a user to process a specially crafted MFER file, which is a local, data-parsing operation rather than a network-exposed service.

Out-of-bounds Write

Libbiosig Project Libbiosig

before 3.9.2

Halo Surface Signal: 1 out of 5 — much less likely to be public-facing.

External exposure likelihood

Horizon Alert

Summary of the vulnerability and why it matters

A critical vulnerability has been identified in The Biosig Project's library, which is used for processing biomedical signal data. This issue could allow for arbitrary code execution if a specially crafted file is processed. While the primary concern is confirming relevance and exposure, understanding this type of risk is important.

Flaw in data processing allows code execution.
Leaders should remember potential for serious system compromise.
Confirm if our systems use this specific library.

Attack Path

How an attacker could exploit the issue

An attacker can target users by sending a specially crafted MFER file. When the recipient opens this file using an application that parses it with the vulnerable libbiosig library, a stack-based buffer overflow can occur. This overflow can lead to arbitrary code execution on the user's system.

Requires user to open a malicious file.
Triggered by parsing a crafted MFER file.
Leads to arbitrary code execution.

Live Threat

Current exploitation, exposure, and threat context

These vulnerabilities in MFER file parsing could allow an attacker to execute arbitrary code when a specially crafted file is processed. This could affect the integrity and availability of systems processing MFER files.

System data integrity and availability.
Malicious MFER file processing.
Arbitrary code execution.

Operational Fix

Recommended remediation, mitigation, and detection steps

This vulnerability impacts systems processing MFER files with the libbiosig library. Ownership likely falls to teams managing data processing pipelines or specific research applications that utilize this library. The first practical step is to identify all systems processing MFER files, determine their criticality, and locate the application or system owners responsible for the libbiosig integration.

Identify MFER processing systems.
Verify asset criticality and exposure.
Plan remediation with application owners.

Supplementary metadata

CVSS vector

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Frequently asked questions

What is the libbiosig library used for?

Libbiosig is a software library designed to help developers read, write, and process various biomedical signal data formats. It is commonly integrated into research tools, medical software, and data analysis pipelines to interpret complex physiological recordings, such as MFER files, which are a standardized format for transferring medical waveform data.

How does this stack-based buffer overflow work in CVE-2025-66043?

This vulnerability involves a memory corruption issue known as a stack-based buffer overflow (CWE-121, CWE-787). It occurs when the library attempts to write more data into a fixed-size memory area than it can hold while parsing an MFER file. Because the program does not properly check the data size, the excess information can overwrite adjacent memory, potentially allowing an attacker to hijack the program's execution flow.

Does simply receiving a malicious MFER file trigger the vulnerability?

No. The vulnerability is not triggered by merely receiving or storing the file. It requires an application that uses libbiosig to actively open and parse a specifically crafted MFER file. If your system merely holds these files without using an affected version of the library to process them, the code execution path is not triggered.

Why does Halo Surface Signal categorize this as unlikely to be internet-facing?

Halo Surface Signal notes that libbiosig is a specialized data-parsing library, not a network-exposed service like a web server or firewall. Because it functions as a component within other applications, it does not typically listen for internet connections. The risk is constrained to systems where a user or automated process intentionally parses untrusted data files.

What is the recommended first step to respond to this CVE?

Begin by auditing your environment to identify software or research tools that rely on libbiosig for processing MFER files. Once you have a list of these systems, verify which ones are running versions earlier than 3.9.2 and confirm if those applications are used to parse data from external or untrusted sources.

References

talosintelligence.com/vulnerability_reports/TALOS-2025-2296

Written by Nicholas Merritt

Nicholas Merritt is VP of Security Solutions at Halo Security. With more than 25 years across application security, vulnerability prioritization, and offensive security, he helps teams translate threat data into practical exposure validation and remediation focus. He authors Halo Threat Intelligence CVE advisories using Halo Surface Signal and H/A/L/O context to prioritize internet-facing risk.