External risk intelligence

libbiosig MFER Parsing Stack Buffer Overflow.

CVE advisorySeverity: CRITICAL (CVSS 9.8)

CVE-2025-66045

libbiosig is a specialized software library used for parsing biomedical file formats (MFER). It is typically integrated into specific research or clinical data analysis applications rather than being exposed as a public-facing network service. The vulnerability requires a user to process a specially crafted file, making it a file-parsing issue rather than an internet-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

This advisory highlights critical vulnerabilities in the MFER parsing functionality of The Biosig Project's libbiosig library. A specially crafted file could allow an attacker to execute arbitrary code, potentially impacting systems that process these specific biomedical data formats. The main concern is confirming relevance and exposure given the specialized nature of the affected technology.

A file processing flaw enables code execution.
Leadership should track potential use in research tools.
Confirm if your biomedical data processing is impacted.

Attack Path

How an attacker could exploit the issue

An attacker can exploit vulnerabilities in the MFER parsing feature by providing a specially crafted MFER file. This malicious file can trigger a stack-based buffer overflow, potentially leading to arbitrary code execution.

No special access or authentication needed.
Triggered by processing a malicious MFER file.
Can lead to arbitrary code execution.

Live Threat

Current exploitation, exposure, and threat context

These vulnerabilities could allow an attacker to execute arbitrary code by tricking a user into processing a specially crafted MFER file, potentially impacting the integrity and availability of the application and its data.

Arbitrary code execution in parsing MFER files.
Malicious file provided to trigger flaws.
Compromise of application and its data.

Operational Fix

Recommended remediation, mitigation, and detection steps

Teams integrating libbiosig into biomedical data analysis applications or research software should lead the response. The first action is to identify all applications that ingest MFER files using this library, determine their criticality, and pinpoint the accountable application owner for coordinated remediation.

Application owners should oversee remediation efforts.
Verify MFER file processing points.
Plan coordinated updates during maintenance windows.

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 the libbiosig library?

The libbiosig library is a specialized software tool designed for biomedical data analysis. Researchers and clinical software developers use it to parse and interpret specific medical file formats, such as the Medical Information Formats for Encoding and Reporting (MFER) standard, which stores biosignal data like ECG or EEG recordings.

What does CVE-2025-66045 mean in plain English?

This vulnerability is a stack-based buffer overflow, classified under CWE-121 and CWE-787. It occurs when the software incorrectly handles large amounts of data while parsing an MFER file, overwhelming the system's memory. This flaw can allow an attacker to overwrite critical memory areas, potentially letting them run unauthorized commands or malicious code on the system processing the file.

How is this vulnerability triggered?

An attacker triggers the vulnerability by providing a specially crafted MFER file to an application that uses the affected libbiosig library. Simply having the library installed is not enough; the bug only activates when a vulnerable version of the software attempts to open and process the malicious file. Normal, valid MFER files do not cause this issue.

Do I need to worry about this vulnerability?

According to Halo Surface Signal, this is very unlikely to be an immediate internet-facing risk. Because libbiosig is a backend library used for specialized data processing rather than a public network service, the risk depends on whether your internal systems ingest untrusted MFER files from external sources. You should focus on applications that automatically handle files from outside your environment.

What are the first steps to fix this?

Your priority is to identify every application in your environment that utilizes libbiosig to parse MFER data. Once identified, determine the risk level of these tools and coordinate with the specific application owners to update the library to version 3.9.2 or later, which resolves these parsing flaws.

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.