CVE-2025-4395

Executive Summary

CVE-2025-4395 is a critical security vulnerability in Medtronic MyCareLink Patient Monitor models 24950 and 24952. The flaw involves a built-in user account with an empty password, allowing an attacker with physical access to log in without authentication and modify system functionality. This vulnerability poses a significant risk to patient safety and device integrity in healthcare environments. The CVSS score is 6.8 (Medium), but the impact on confidentiality, integrity, and availability is high given the medical context. No public exploit code or proof-of-concept is currently available, and no patch has been released as of the advisory date.

CVSS Breakdown & Threat Level

• CVSS Vector: CVSS:3.1/AV:P/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
• Base Score: 6.8 (Medium)
• Attack Vector: Physical (AV:P) – Requires physical access to the device.
• Attack Complexity: Low (AC:L) – No special conditions required.
• Privileges Required: None (PR:N) – No authentication needed.
• User Interaction: None (UI:N) – No user action required.
• Scope: Unchanged (S:U) – Vulnerability affects only the device.
• Confidentiality Impact: High (C:H) – Full access to patient data and device configuration.
• Integrity Impact: High (I:H) – Ability to modify system settings and potentially alter device behavior.
• Availability Impact: High (A:H) – Could disrupt monitoring functions or cause denial of service.

Threat Level: High for healthcare environments due to potential for patient harm, data breach, and device manipulation.

Deep Dive & Mechanics

The vulnerability stems from a hardcoded user account with an empty password in the Medtronic MyCareLink Patient Monitor firmware. This account is intended for maintenance or emergency access but lacks any password requirement, making it trivial to exploit with physical access.

Technical Details:

• The device runs a custom embedded Linux-based operating system.
• The built-in account (likely named "root" or "admin") has an empty password field in the /etc/shadow or equivalent authentication database.
• The device's login interface (either a physical keyboard/monitor or a serial console) accepts empty passwords for this account.
• Once logged in, the attacker gains root or administrative privileges, allowing modification of system files, patient data, network settings, and monitoring parameters.

Attack Scenario:

1. Attacker gains physical access to the MyCareLink monitor (e.g., in a hospital room, clinic, or during transport).
2. Attacker connects a keyboard or uses the device's built-in interface to access the login prompt.
3. Attacker enters the built-in username (e.g., "admin") and leaves the password field blank.
4. Attacker gains full system access and can modify device behavior, exfiltrate patient data, or disable monitoring.

Vulnerable vs. Patched Code

Since no patch is available, the vulnerable code is the authentication mechanism that accepts empty passwords. A patched version would require:

• Vulnerable: Authentication function that compares user input to an empty string for the password field.
• Patched: Authentication function that rejects empty passwords or requires a non-empty, complex password.

Example (Pseudocode):

// Vulnerable code
if (strcmp(username, "admin") == 0 && strcmp(password, "") == 0) {
    grant_access();
}

// Patched code
if (strcmp(username, "admin") == 0 && strlen(password) > 0 && verify_password(password)) {
    grant_access();
}

Exploitation & Lab Setup

Red Team (Exploitation)

Prerequisites:

• Physical access to Medtronic MyCareLink Patient Monitor (models 24950 or 24952).
• Keyboard or serial console connection.

Steps:

1. Power on the device or ensure it is in an idle state.
2. Connect a USB keyboard to the device's USB port or use the built-in touchscreen/keypad.
3. At the login prompt, enter the built-in username (commonly "admin" or "root").
4. Leave the password field empty and press Enter.
5. Upon successful login, you will have root or administrative shell access.

Commands after access:

# Check current user
whoami

# List all users
cat /etc/passwd

# Modify system settings (example: disable logging)
systemctl stop syslog

# Exfiltrate patient data (example)
tar -czf /tmp/patient_data.tar.gz /var/patient_data/

Blue Team (Defense & Detection)

Detection:

• Monitor for physical access attempts to the device (e.g., via security cameras, access logs).
• Enable device logging and audit login attempts (if supported).
• Use network monitoring to detect unusual traffic from the device (e.g., data exfiltration).

Mitigation:

• Restrict physical access to the device to authorized personnel only.
• Implement additional authentication mechanisms (e.g., two-factor, smart card) if possible.
• Apply vendor patches when available.
• Consider network segmentation to isolate medical devices.

Indicators of Compromise (IOCs)

• Network:
  • Unusual outbound connections from the device to unknown IPs.
  • Large data transfers from the device (e.g., patient data exfiltration).
• System:
  • Unexpected changes to system configuration files.
  • New user accounts or modified passwords.
  • Disabled logging or security services.
• Physical:
  • Unauthorized personnel near the device.
  • Tampering with device ports (USB, serial).

Detection Engineering

YARA Rule

rule CVE_2025_4395_Empty_Password_Account {
    meta:
        description = "Detects Medtronic MyCareLink Patient Monitor with empty password account"
        author = "Valters IT"
        date = "2025-04-10"
        reference = "CVE-2025-4395"
    strings:
        $empty_pw = /admin::/ nocase
        $root_empty = /root::/ nocase
    condition:
        any of them
}

Sigma Rule

title: Medtronic MyCareLink Empty Password Login
id: 12345678-1234-1234-1234-123456789012
status: experimental
description: Detects successful login with empty password on Medtronic MyCareLink Patient Monitor
author: Valters IT
date: 2025-04-10
references:
    - https://nvd.nist.gov/vuln/detail/CVE-2025-4395
logsource:
    product: linux
    service: auth
detection:
    selection:
        EventID: 1  # Successful login
        User: "admin"
        Password: ""
    condition: selection
falsepositives:
    - Legitimate maintenance access (should be rare)
level: high

Suricata Rule

alert tcp $HOME_NET any -> $EXTERNAL_NET any (msg:"CVE-2025-4395 Medtronic MyCareLink Data Exfiltration"; flow:to_server,established; content:"|50 61 74 69 65 6e 74 20 44 61 74 61|"; nocase; sid:1000001; rev:1;)

Remediation & Mitigation

Immediate Actions:

1. Restrict physical access to MyCareLink devices to authorized personnel only.
2. Implement additional physical security controls (e.g., locked cabinets, tamper-evident seals).
3. Monitor device logs for unauthorized login attempts.
4. Disable or remove the built-in account if possible (consult vendor documentation).

Long-term Fix:

• Apply vendor patch when available (expected after June 25, 2025).
• Replace affected devices with newer models that enforce password policies.
• Implement network segmentation and intrusion detection for medical devices.

Workaround:

• If the device allows, change the password for the built-in account via the device's administrative interface.
• Use a firewall to restrict outbound connections from the device.

Valters IT