Btproxy - Man In The Middle Analysis Tool For Bluetooth

Monday, October 19, 2015

Tested Devices
  • Pebble Steel smart watch
  • Moto 360 smart watch
  • OBDLink OBD-II Bluetooth Dongle
  • Withings Smart Baby Monitor
If you have tried anything else, please let me know at conorpp (at) vt (dot) edu.

  • Need at least 1 Bluetooth card (either USB or internal).
  • Need to be running Linux, another *nix, or OS X.
  • BlueZ 4
For a debian system, run
sudo apt-get install bluez bluez-utils bluez-tools libbluetooth-dev python-dev

sudo python install

To run a simple MiTM or proxy on two devices, run
btproxy <master-bt-mac-address> <slave-bt-mac-address>
Run btproxy to get a list of command arguments.

# This will connect to the slave 40:14:33:66:CC:FF device and 
# wait for a connection from the master F1:64:F3:31:67:88 device
btproxy F1:64:F3:31:67:88 40:14:33:66:CC:FF
Where the master is typically the phone and the slave mac address is typically the other peripherial device (smart watch, headphones, keyboard, obd2 dongle, etc).
The master is the device the sends the connection request and the slave is the device listening for something to connect to it.
After the proxy connects to the slave device and the master connects to the proxy device, you will be able to see traffic and modify it.

How to find the BT MAC Address?
Well, you can look it up in the settings usually for a phone. The most robost way is to put the device in advertising mode and scan for it.
There are two ways to scan for devices: scanning and inquiring. hcitool can be used to do this:
hcitool scan
hcitool inq
To get a list of services on a device:
sdptool records <bt-address>

Some devices may restrict connecting based on the name, class, or address of another bluetooth device.
So the program will lookup those three properties of the target devices to be proxied, and then clone them onto the proxying adapter(s).
Then it will first try connecting to the slave device from the cloned master adaptor. It will make a socket for each service hosted by the slave and relay traffic for each one independently.
After the slave is connected, the cloned slave adaptor will be set to be listening for a connection from the master. At this point, the real master device should connect to the adaptor. After the master connects, the proxied connection is complete.

Using only one adapter
This program uses either 1 or 2 Bluetooth adapters. If you use one adapter, then only the slave device will be cloned. Both devices will be cloned if 2 adapters are used; this might be necessary for more restrictive Bluetooth devices.

Advanced Usage
Manipulation of the traffic can be handled via python by passing an inline script. Just implement the master_cb and slave_cb callback functions. This are called upon receiving data and the returned data is sent back out to the corresponding device.
def master_cb(req):
        Received something from master, about to be sent to slave.
    print '<< ', repr(req)
    open('mastermessages.log', 'a+b').write(req)
    return req

def slave_cb(res):
        Same as above but it's from slave about to be sent to master
    print '>> ', repr(res)
    open('slavemessages.log', 'a+b').write(res)
    return res
Also see the example functions for manipulating Pebble watch traffic in
This code can be edited and reloaded during runtime by entering 'r' into the program console. This avoids the pains of reconnecting. Any errors will be caught and regular transmission will continue.

  • BLE
  • Improve the file logging of the traffic and make it more interactive for
  • replays/manipulation.
  • Indicate which service is which in the output.
  • Provide control for disconnecting/connecting services.
  • PCAP file support
  • ncurses?

How it works
This program starts by killing the bluetoothd process, running it again with a LD_PRELOAD pointed to a wrapper for the bind system call to block bluetoothd from binding to L2CAP port 1 (SDP). All SDP traffic goes over L2CAP port 1 so this makes it easy to MiTM/forward between the two devices and we don't have to worry about mimicking the advertising.
The program first scans each device for their name and device class to make accurate clones. It will append the string '_btproxy' to each name to make them distinguishable from a user perspective. Alternatively, you can specify the names to use at the command line.
The program then scans the services of the slave device. It makes a socket connection to each service and open a listening port for the master device to connect to. Once the master connects, the Proxy/MiTM is complete and output will be sent to STDOUT.

Some bluetooth devices have different methods of pairing which makes this process more complicated. Right now it supports SPP and legacy pin pairing.
This program doesn't yet have support for Bluetooth Low Energy. A similiar approach to BLE can be taken.


btproxy or bluetoothd hangs
If you are using bluez 5, you should try uninstalling and installing bluez 4 . I've had problems with bluez 5 hanging.

error accessing bluetooth device
Make sure the bluetooth adaptors are plugged in and enabled.
    # See the list of all adaptors
    hciconfig -a

    # Enable
    sudo hciconfig hciX up

    # if you get this message
    Can't init device hci0: Operation not possible due to RF-kill (132)

    # Then try unblocking it with the rfkill command
    sudo rfkill unblock all

UserWarning: <path>/.python-eggs is writable by group/others
chmod g-rw,o-x <path>/.python-eggs

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