Pentesting BLE - Bluetooth Low Energy

Reading time: 4 minutes

Introduction

Available since the Bluetooth 4.0 specification, BLE uses only 40 channels, covering the range of 2400 to 2483.5 MHz. In contrast, traditional Bluetooth uses 79 channels in that same range.

BLE devices communicate is by sending advertising packets (beacons), these packets broadcast the BLE device’s existence to other nearby devices. These beacons sometimes send data, too.

The listening device, also called a central device, can respond to an advertising packet with a SCAN request sent specifically to the advertising device. The response to that scan uses the same structure as the advertising packet with additional information that couldn’t fit on the initial advertising request, such as the full device name.

The preamble byte synchronizes the frequency, whereas the four-byte access address is a connection identifier, which is used in scenarios where multiple devices are trying to establish connections on the same channels. Next, the Protocol Data Unit (PDU) contains the advertising data. There are several types of PDU; the most commonly used are ADV_NONCONN_IND and ADV_IND. Devices use the ADV_NONCONN_IND PDU type if they don’t accept connections, transmitting data only in the advertising packet. Devices use ADV_IND if they allow connections and stop sending advertising packets once a connection has been established.

GATT

The Generic Attribute Profile (GATT) defines how the device should format and transfer data. When you’re analyzing a BLE device’s attack surface, you’ll often concentrate your attention on the GATT (or GATTs), because it’s how device functionality gets triggered and how data gets stored, grouped, and modified. The GATT lists a device’s characteristics, descriptors, and services in a table as either 16- or 32-bits values. A characteristic is a data value sent between the central device and peripheral. These characteristics can have descriptors that provide additional information about them. Characteristics are often grouped in services if they’re related to performing a particular action.

Enumeration

hciconfig #Check config, check if UP or DOWN
# If DOWN try:
sudo modprobe -c bluetooth
sudo hciconfig hci0 down && sudo hciconfig hci0 up

# Spoof MAC
spooftooph -i hci0 -a 11:22:33:44:55:66

GATTool

GATTool allows to establish a connection with another device, listing that device’s characteristics, and reading and writing its attributes.
GATTTool can launch an interactive shell with the -I option:

gatttool -i hci0 -I
[ ][LE]> connect 24:62:AB:B1:A8:3E Attempting to connect to A4:CF:12:6C:B3:76 Connection successful
[A4:CF:12:6C:B3:76][LE]> characteristics
  handle: 0x0002, char properties: 0x20, char value handle:
  0x0003, uuid: 00002a05-0000-1000-8000-00805f9b34fb
  handle: 0x0015, char properties: 0x02, char value handle:
  0x0016, uuid: 00002a00-0000-1000-8000-00805f9b34fb
[...]

# Write data
gatttool -i <Bluetooth adapter interface> -b <MAC address of device> --char-write-req <characteristic handle> -n <value>
gatttool -b a4:cf:12:6c:b3:76 --char-write-req -a 0x002e -n $(echo -n "04dc54d9053b4307680a"|xxd -ps)

# Read data
gatttool -i <Bluetooth adapter interface> -b <MAC address of device> --char-read -a 0x16

# Read connecting with an authenticated encrypted connection
gatttool --sec-level=high -b a4:cf:12:6c:b3:76 --char-read -a 0x002c

Bettercap

# Start listening for beacons
sudo bettercap --eval "ble.recon on"
# Wait some time
>> ble.show # Show discovered devices
>> ble.enum <mac addr> # This will show the service, characteristics and properties supported

# Write data in a characteristic
>> ble.write <MAC ADDR> <UUID> <HEX DATA>
>> ble.write <mac address of device> ff06 68656c6c6f # Write "hello" in ff06