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Frankenstein provides a virtual environment to fuzz wireless firmwares. Firmwares can be hooked during runtime to extract their current state (i.e., xmitstate through InternalBlue). Then, they can be re-executed in a virtual environment for fuzzing. To do so, the firmware image needs to be reassembled to an ELF file that can be executed with QEMU. The firmware image reassembly is simplified by a web-based UI.

Frankenstein is currently optimized for the CYW20735 Bluetooth evaluation board. The slightly newer CYW20819 Bluetooth evaluation board is already partially supported. The port to the CYW20819 evaluation board is required due to CVE-2019-18614, which prevents further fuzzing of connection states such as music streaming or tethering. We are working on support for the Samsung Galaxy S10/S20—all of the European S10e/S10/S10+/Note 10/S20 models feature the same chip. If you already have symbols for one chip but are missing symbols for a chip that had similar compiler options, you might find using Polypyus before running BinDiff helpful.

Table of Contents

Basic Setup

This tool contains a web-based UI to configure the build. This includes management of symbols and memory dumps. The Makefile and linker scripts are generated automatically by the build system. The build system can be launched by the following command and navigating the browser to http://127.0.0.1:8000/

python3 manage.py runserver

The build system already contains symbols and an initial memory dump. You can browse through the available projects and the dump without having the actual hardware, IDA Pro or Ghidra database, etc. Symbols are truncated to the first 1k symbols, so do not worry if something you know does not show up in the list immediately.

Each firmware version is located in a different project stored in projects. A project contains the file project.json, which holds the symbol names and the memory layout including memory dumps. The available symbols can be used to generate patches in C as well as for firmware emulation. To build all patches and emulators for the CYW20735 evaluation board run:

make -C projects/CYW20735B1

In general, having the project built is sufficient to run emulation with QEMU. However, for fuzzing it can be quite interesting to hold the firmware at a different state and continue fuzzing from there. So, if you currently do not have any of our supported hardware, you can skip the xmitstate step later.

After rebuilding the project using make -C projects/CYW20735B1, the firmware state can be emulated, until the Idle thread is entered. For this, execute:

qemu-arm projects/CYW20735B1/gen/execute.exe

Or execute it from the web frontend and get even more insights:

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Attaching the Firmware to a Host

The basic execute.exe ELF file does not communicate to the outside world. Thus, it terminates in the Idle thread. However, for fuzzing the firmware, it needs to be attached to a real host and obtain random "wireless" inputs.

We provide an additional patch in hci_attach.exe that abstracts the calling conventions for the Bluetooth Core Scheduler (BCS). The BCS normally takes inputs from the hardware registers that contain decoded packets from the physical layer. We replace the invocation of the interrupt handler bluetoothCoreInt_C that calls the BCS every 312.5µs (1/2 Bluetooth clock cycle). This interrupt handler is now reading data from standard input (STDIN) of the Linux host. You can feed arbitrary inputs, i.e., data from /dev/urandom.

cat /dev/urandom | qemu-arm projects/CYW20735B1/gen/hci_attach.exe

Note that hci_attach.exe also calls the btattach command on the host, which is part of the Linux Bluez Bluetooth stack. Once you run this file, your host will have a new Bluetooth device. You can list the current devices with hciconfig. The hook to pass UART data from the emulated device to the Linux host is installed in the firmware functions uart_directWrite and similar functions.

Depending on the host's exact behavior, you might need to reset the chip immediately after starting QEMU. Otherwise, emulation will get stuck or segfault. On a current (September 2019) Debian testing, this is not done automatically by the host and can be done manually as follows:

hcitool -i hci1 cmd 0x03 0x03
    < HCI Command: ogf 0x03, ocf 0x0003, plen 0
    > HCI Event: 0x0e plen 4
      01 03 0C 00

After successful reset, the emulation keeps running, which means that you will see a lot of output within short time on the terminal that started the hci_attach.exe. Now you can start actions on the host that cause interaction with the emulated Bluetooth firmware. For example, you can scan for Bluetooth LE devices:

hcitool -i hci1 lescan

If you open Wireshark while doing so, you will notice a lot of weird and invalid packets. Nonetheless, the scanning output will show a lot of devices with random addresses within short time, with some of these even returning mal-formatted names.

Reproducing CVEs

To trigger CVE-2019-11516, run hcitool -i hci1 scan and wait a couple of seconds to minutes.

Context switch idle -> lm
lr=0x02d12f lm_handleInqFHS(0x40)lr=0x02cc53 lc_handleInqResult(0x21fb1c)lr=0x041d91 inqfilter_isBdAddrRegistered(0x21fb24, 0x0);
lr=0x041dc3 inqfilter_registerBdAddr(0x21fb24, 0x0);
lr=0x041dfb bthci_event_SendInquiryResultEvent(0x21fb1c)lr=0x024e49 dynamic_memory_AllocateOrDie(0x19)Heap Corruption Detected
pool = 0x20d368
pool->size = 0x0180
free_chunk = 0x221c04
7f7fb0c9 | a3e4b4aa4242424242424242424242424242424242424242424242424242424242424242
    4242424242424242424242424242424242424242424242424242424242424242424242424242424
    2424242424242424242424242424242424242424242424242424242424242424242424242424242
    4242424242424242424242424242424242424242424242424242424242424242424242424242424
    2424242424242424242424242424242424242424242424242424242424242424242424242424242
    4242424242424242424242424242424242424242424242424242424242424242424242424242424
    2424242424242424242424242424242424242424242424242424242424242424242424242424242
    4242424242424242424242424242424242424242424242424242424242424242424242424242424
    2424242424242424242424242424242424242424242424242424242424242424242424242424242
    4242424242424242424242424242424242424242424242424242424242424242
qemu: uncaught target signal 11 (Segmentation fault) - core dumped

For debugging purposes, our heap sanitizer is currently writing 0x42 to released memory.

Now let's trigger CVE-2019-13916. As this vulnerability is within parsing of BLE PDUs, all you need to do is to successfully establish a connection to another LE device. If you connect to random addresses, this will succeed at some point in time. Usually, this takes a couple of minutes and in some cases the emulator crashes instead and you need to restart the emulation. Be patient!

while true; do hcitool -i hci1 lecc ca:fe:ba:be:13:37; done

This results in:

lr=0x08ee3d bcsulp_getPktLength(0x854cfecd, 0x0) = 0xfe;
lr=0x08ed33 bcsulp_getPktLength(0x05, 0x0) = 0x0;
lr=0x08ec11 bcsulp_getPktLength(0x05, 0x0) = 0x0;
lr=0x08ebc1 dhmulp_getTxBuffer(0x281704, 0x1b, 0x0148001b);
lr=0x041e95 bcsulp_getPktLength(0x854cfecd, 0x0) = 0xfe;
lr=0x08f115 bcsulp_procRxPayload(0x281618, 0x854cfecd)lr=0x08e9c3 bcsulp_getPktLength(0x854cfecd, 0x0) = 0xfe;
lr=0x08ea2f bcsulp_getPktLength(0x854cfecd, 0x0) = 0xfe;
lr=0x08ea4b utils_memcpy8(0x2232d0, 0x370c00, 0xfe)Heap Corruption Detected
pool = 0x20d38c
pool->block_start = 0x2232c0
pool->capacity = 0x0f
pool->size = 0x0108
free_chunk = 0x1010a9a8

qemu: uncaught target signal 11 (Segmentation fault) - core dumped

Dumping Custom States

To dump a custom state, the most important patch is patch/xmit_state.h. It generates re-executable firmware states. It is used in a custom InternalBlue extension internalBlueMod.py. If you are running on a native Linux and want to access the raw HCI device, you need superuser rights.

(sudo) python3 internalBlueMod.py

In this extension, we can run the following command to generate a re-executable state:

> xmitstate target_function

Depending on the target function, this might crash sometimes. Just try again. Once you successfully dumped a state, InternalBlue will finish with

[*] Received fuill firmware state

If the firmware crashes afterwards, you can ignore this.

Now, reload the web UI running on http://127.0.0.1:8000/. It will list your new dump in the Segment Groups view, i.e., internalBlue_09.24.2019_18.32.09. The most recent dump will automatically be set to the Active state. You can now build the project again.

If you were running InternalBlue with sudo, you might need to adjust access rights to the generated state. To do so, run:

sudo chown -R $USER:$USER projects/CYW20735B1/segment_groups/

Now, build the project again:

make -C projects/CYW20735B1

Live Heap Sanitizer

Run our customized InternalBlue script on real hardware:

(sudo) python3 internalBlueMod.py

Load the heap sanitizer patch on top:

> loadelf projects/CYW20735B1/gen/heap_sanitizer.patch

Now you will get detailed output about heap violations, i.e., caused by memcpy and the function which called it. Depending on what you debug, you might need to adjust the definitions in patch/heap_sanitizer.c.

Important Notes & Dependencies

Frankenstein depends on InternalBlue. Projects must be named by the chip descriptions in the InternalBlue firmware files. For example, internalblue/fw/fw_0x4208.py contains the firmware for the CYW20735 evaluation board and contains the identifier FW_NAME = "CYW20735B1". Thus, the Frankenstein project name is CYW20735B1.

For QEMU, you need to install the qemu-user package. Compilation of the project requires gcc-arm-none-eabi.

apt install qemu-user gcc-arm-none-eabi gcc-multilib

Tested with qemu-user (1:3.1+dfsg+8+deb10u2) and gcc-arm-none-eabi (15:7-2018-q2-6) and gcc-multilib (4:8.3.0-1).

The following Python 3 packets are required:

pip3 install django pyelftools==0.24

Tested with django-1.11.24.

We thank Anna Stichling for creating the Frankenstein logo.