DVID Writeup 05 - Bluetooth - Characteristics

2-minute read
writeup
dvid • firmware • iot
Table of contents :

If you’re not yet familiar with the Damn Vulnerable Iot Device (DVID) project, I encourage you to read the project presentation page.

Goal of this challenge

One time password bluetooth device. This IoT device should work with an android application, but you don’t have it. The goal is to provide a screenshot of the password

Something is leaking on 0000ffe1.

Flashing the board

First things first, we are going to flash the firmware for this challenge onto the DVID board. In order to do this, we will use avrdude and an USB AVR programmer. If you’re not familiar with avrdude options I encourage you to read the flashing the board section of the first DVID writeup of this series. We will flash the board using this nice flash.sh script :

#!/bin/bash

if [[ ! -d "./DVID/" ]]; then
    git clone https://github.com/vulcainreo/DVID
fi

pushd ./DVID/trainings/bluetooth/characteristics/
avrdude -F -v -p atmega328p -P /dev/ttyUSB0 -c usbasp -u -U flash:w:characteristics.ino.with_bootloader.arduino_standard.hex
popd

Now, we will connect the DVID board to our computer using the USB AVR programmer, and start the script. When the AVR programming has completed, the board should restart and you should see this :

Boot screen

Solving the challenge

In this challenge, the IoT device sends informations using bluetooth characteristics on 0000ffe1. Firstly, we need to do a bluetooth scan to find the device. We can do this inside bluetoothctl using scan on command. (and scan off to stop).

bluetoothctl scan

Now that we found the IoT device, we can connect to it by typing connect followed by the device’s bluetooth address.

bluetoothctl connect

To use bluetooth characteristics, we need to use a specific menu, called gatt. To access it in bluetoothctl, type menu gatt to enter the gatt menu and back to exit the menu. In the gatt menu we have access to many advanced features, such as listing attributes of a device, reading and writing data to bluetooth services :

bluetoothctl menu gatt

We will now list attributes offered by the bluetooth device using list-attributes command :

bluetoothctl list-attributes

Looking at the screen of the DVID device, we can see a message “Something is leaking on 0000ffe1”, therefore we will try to interact with the characteristic 0000ffe1-0000-1000-8000-00805f9b34fb. To do this, we need to select the attribute using select-attribute <uuid> command :

bluetoothctl select-attribute

Then we need to acquire-notify to connect to the stream and be able to read the values from the service/characteristic. We can then type read to read the stream of values comming from the service/characteristic.

bluetoothctl read value

And we have the flag !

Additional references