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BLE Security: Preventing MiTM Attacks

G5 Cyber Security

TL;DR

Bluetooth Low Energy (BLE) is vulnerable to Man-in-the-Middle (MiTM) attacks. This guide explains how these attacks work and provides practical steps to protect your devices and data, focusing on pairing methods, encryption, and monitoring for suspicious activity.

Understanding the Threat

A MiTM attack intercepts communication between two BLE devices – typically a central device (like a phone) and a peripheral device (like a fitness tracker). The attacker pretends to be one of these devices, allowing them to read, modify, or even inject data into the conversation. Because BLE often relies on trust established during pairing, it’s crucial to understand how that trust is created.

How MiTM Attacks Work

  1. Passive Listening: An attacker uses a BLE scanner to listen for devices broadcasting advertising packets.
  2. Impersonation: The attacker spoofs the identity of either the central or peripheral device. This can involve replaying previously captured data or actively generating new packets.
  3. Interception & Manipulation: Once a connection is established with the victim device, the attacker intercepts and potentially modifies the data exchanged.

Protecting Against BLE MiTM Attacks

Here’s how to mitigate the risk:

1. Secure Pairing Methods

  1. Just Works Pairing (Avoid): This is the simplest pairing method, offering no authentication and being highly susceptible to MiTM attacks. It should be avoided whenever possible.
  2. Numeric Comparison Pairing: Both devices display a number; the user confirms they match. More secure than ‘Just Works’, but still vulnerable if the attacker can intercept and display the correct number simultaneously.
  3. Passkey Entry Pairing: The user enters a passkey on both devices. This is significantly more secure, especially with longer, randomly generated passkeys.
  4. Out-of-Band (OOB) Pairing: Uses an alternative communication channel (e.g., NFC, QR code) to exchange pairing information securely. The most robust method.

Always choose the strongest available pairing method supported by your devices. Check device documentation for details.

2. Encryption

  1. Ensure Encryption is Enabled: BLE uses encryption to protect data in transit. Verify that both devices are configured to use encryption after successful pairing.
  2. Understand Security Modes: BLE has different security modes (e.g., Mode 1, Mode 2, Mode 3). Higher modes offer better protection but may impact performance.

Most modern BLE stacks handle encryption automatically after a secure pairing process. However, it’s good to be aware of the underlying mechanisms.

3. Monitoring and Detection

  1. Regularly Scan for Unknown Devices: Use a BLE scanner app on your phone to identify any unfamiliar devices in your vicinity.
  2. Look for Suspicious Advertising Data: Pay attention to the names and services advertised by nearby devices. Unusual or misleading information could indicate an attacker.
  3. Check Connection Logs (Advanced): Some operating systems provide logs of BLE connections. Review these logs for unexpected pairings or disconnections. On Linux, you might use tools like 
    bluetoothctl

    to inspect connection details.

  4. Firmware Updates: Keep your devices’ firmware up-to-date. Manufacturers often release updates that address security vulnerabilities.

4. Device Specific Considerations

  1. Fitness Trackers/Smartwatches: Be cautious when pairing with public kiosks or unknown networks. Enable passkey entry pairing whenever possible.
  2. IoT Devices: Secure your IoT devices by changing default credentials and enabling encryption. Consider using OOB pairing if available.
  3. Mobile Apps: Only connect to BLE devices through trusted apps from reputable developers. Review app permissions carefully.

Further Resources

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