External risk intelligence

libbiosig MFER Parsing Stack Buffer Overflow Leads to Code Execution

CVE advisorySeverity: CRITICAL (CVSS 9.8)

CVE-2025-66046

libbiosig is a specialized software 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 manually process a specially crafted file, making it a client-side or offline processing risk rather than a publicly exposed network 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 in the libbiosig library allows for arbitrary code execution when processing specially crafted MFER files, posing a potential risk if these files are handled by affected systems. The primary concern is confirming whether this specialized library is in use within the organization's environment.

Malicious files could execute code on processing systems.
A specialized library's relevance requires confirmation.
Assess exposure; confirmed use requires immediate attention.

Attack Path

How an attacker could exploit the issue

An attacker could exploit these vulnerabilities by providing a specially crafted MFER file to a user. If the user opens this malicious file, it could lead to arbitrary code execution. The vulnerabilities are located in the MFER parsing functionality of libbiosig.

Malicious MFER file provided.
MFER parsing functionality triggered.
Arbitrary code execution possible.

Live Threat

Current exploitation, exposure, and threat context

The MFER parsing functionality in libbiosig could be exploited by a specially crafted file, leading to arbitrary code execution when supported by the advisory.

MFER parsing functionality.
Malicious file provided by an attacker.
Arbitrary code execution.

Operational Fix

Recommended remediation, mitigation, and detection steps

This vulnerability in the MFER parsing functionality of libbiosig, particularly when processing Tag 67, presents a critical risk for any systems that handle or process MFER files. The most immediate operational step is to identify all instances of libbiosig, verify if they process external MFER files, and confirm which teams own these processing workflows to initiate a risk-based remediation plan.

Identify MFER processing systems.
Verify business criticality and exposure.
Plan remediation with accountable owners.

Supplementary metadata

CVSS vector

Validate whether this threat affects your internet-facing exposure.

Halo Threat Intelligence helps prioritize remediation with Halo Surface Signal and H/A/L/O context. Start exposure validation with a free external attack surface trial.

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Frequently asked questions

What is libbiosig?

libbiosig is a specialized software library used by researchers and biomedical engineers to read, write, and analyze biomedical signal data. It is commonly integrated into software tools for processing electrophysiological recordings, such as EEG or ECG files, allowing systems to interpret complex medical data formats like MFER.

What does CWE-121 and CWE-787 mean for CVE-2025-66046?

These codes identify stack-based buffer overflows. In simple terms, the software fails to properly check the size of incoming data before storing it in a fixed-size memory area called the stack. By sending a malicious MFER file, an attacker can overwrite adjacent memory, potentially forcing the program to execute unauthorized commands instead of its intended task.

How is this vulnerability triggered?

The flaw is triggered when the library parses a specially crafted MFER file, specifically involving Tag 67. The vulnerability is not triggered by simply having the library installed; it requires the software to actively open and process a malicious file provided by an attacker.

Is my system at risk according to Halo Surface Signal?

Halo Surface Signal indicates that high-risk internet exposure is very unlikely for this library. Because libbiosig is a specialized tool for offline file processing rather than a network-facing service or web application, the primary risk is limited to systems where users manually handle or process untrusted biomedical data files.

What should I do if I use libbiosig?

First, locate where libbiosig is used in your environment and determine if those systems process external or untrusted MFER files. Once you identify these workflows, prioritize updating the library to version 3.9.2 or later to resolve the parsing issue. Coordinate with the technical teams managing these data pipelines to ensure the patch is applied.

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.