BootStomp: An Android boot-loader Bug Finder

BootStomp: An Android boot-loader Bug Finder

To run BootStomp's analyses, please read the following instructions. Note that BootStomp works with boot-loaders compiled for ARM architectures (32 and 64 bits both) and that results might slightly vary depending on angr and Z3's versions. This is because of the time angr takes to analyze basic blocks and to Z3's expression concretization results.

It looks for two different class of bugs: memory corruption and state storage vulnerabilities. For more info please refer to the BootStomp paper at https://seclab.cs.ucsb.edu/academic/publishing/#bootstomp-security-bootloaders-mobile-devices-2017

How does BootStomp find Android Vulnerabilities?

BootStomp implements a multi-tag taint analysis resulting from a novel combination of static analyses and dynamic symbolic execution, designed to locate problematic areas where input from an attacker in control of the OS can compromise the bootloader’s execution or its security features.

Using the tool the team found six previously-unknown vulnerabilities (of which five have been confirmed by the respective vendors), as well as rediscovered one that had been previously reported. Some of these vulnerabilities would allow an attacker to execute arbitrary code as part of the bootloader (thus compromising the entire chain of trust), or to perform permanent denial-of-service attacks.

The team analyzed bootloader implementations in many platforms, including Huawei P8 ALE-L23 (Huawei / HiSilicon chipset), Sony Xperia XA (MediaTek chipset), Nexus 9 (NVIDIA Tegra chipset), and two versions of the LK-based bootloader (Qualcomm).

Directory structure

analysis: Contains analysis results (Ex: IDA idbs etc) of boot images of different devices.
tools: Contains tools that can be used to work with various images.

Pre-requisites

angr (http://angr.io/)
$ pip install angr

• IDA PRO (https://www.hex-rays.com/products/ida/)
• IDA Decompiler (https://www.hex-rays.com/products/decompiler/)

How to run it?

Run BootStomp using docker

The easiest way to use BootStomp is to run it in a docker container. The folder docker contains an appropriate Dockerfile. These are the commands to use it.

cd docker
# build the docker image
docker build -t bootstomp .
# run the docker image (if you need, use proper options to have persistent changes or shared files)
docker run -it bootstomp

# now you are inside a docker container
cd BootStomp
# run BootStomp's taint analysis on one of the examples
# this will take about 30 minutes
python taint_analysis/bootloadertaint.py config/config.huawei
# the last line of the output will be something like:
# INFO    | 2017-10-14 01:54:10,617 | _CoreTaint | Results in /tmp/BootloaderTaint_fastboot.img_.out

# you can then "pretty print" the results using:
python taint_analysis/result_pretty_print.py /tmp/BootloaderTaint_fastboot.img_.out

The output should be something like this:

17)
===================== Start Info path =====================
Dereference address at: 0x5319cL
Reason: at location 0x5319cL a tainted variable is dereferenced and used as address.
...
Tainted Path 
----------------
0x52f3cL -> 0x52f78L -> 0x52f8cL -> 0x52fb8L -> 0x52fc8L -> 0x52fecL -> 0x53000L -> 0x53014L -> 0x5301cL -> 0x53030L -> 0x53044L -> 0x53050L -> 0x5305cL -> 0x53068L
===================== End Info path =====================
# Total sinks related alerts: 5
# Total loop related alerts: 8
# Total dereference related alerts: 4

Run BootStomp manually

Automatic detection of taint sources and sinks

1. Load the boot-loader binary in IDA (we used v6.95). Depending on the CPU architecture of the phone it has been extracted from, 32 bit or 64 bit IDA is needed.
2. From the menu-bar, run File => Script file => find_taint.py
3. Output will appear in the file taint_source_sink.txt under the same directory as the boot-loader itself.

Configuration file

Create a JSON configuration file for the boot-loader binary (see examples in config/), where:

bootloader: boot-loader file path
info_path: boot-loader source/sink info file path (i.e., taint_source_sink.txt )
arch: architecture's number of bits (available options are 32 and 64)
enable_thumb: consider thumb mode (when needed) during the analysis
start_with_thumb: starts the analysis with thumb mode enabled
exit_on_dec_error: stop the analysis if some instructions cannot be decoded
unlock_addr: unlocking function address. This field is necessary only for finding insecure state storage vulnerabilities.

Finding memory corruption vulnerabilities

Run

python bootloadertaint.py config-file-path

Results will be stored in /tmp/BootloaderTaint_[boot-loader].out, where [boot-loader] is the name of the analyzed boot-loader. Note that paths involving loops might appear more than once.

Finding insecure state storage vulnerability
Run

python unlock_checker.py config-file-path

Results will be stored in /tmp/UnlockChecker_[boot-loader].out, where [boot-loader] is the name of the analyzed boot-loader. Note that paths involving loops might appear more than once.

Checking results

To check BootStomp results, use the script result_pretty_print.py, as follows:

python result_pretty_print.py results_file

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