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DroidLysis: pre-analysis script for suspicious Android samples

Project description

DroidLysis

DroidLysis is a property extractor for Android apps. It automatically disassembles the Android application you provide and looks for various properties within the package or its disassembly.

DroidLysis can be used over Android packages (apk), Dalvik executables (dex), Zip files (zip), Rar files (rar) or directories of files.

Install

Requirements

  1. Install required system packages: Python3, Pip, unzip: sudo apt-get install default-jre git python3 python3-pip unzip wget libmagic-dev
  2. Install Android disassembly tools. DroidLysis does not perform the disassembly itself, but relies on other tools to do so. Therefore, you must install:
  • Apktool - note we only need the Jar.
  • Baksmali - note we only need the Jar.

Optional

  • Dex2jar - dex2jar is now optional. If you don't need Dex to Jar transformation (useful for later decompiling!), you can skip it.
  • Procyon - optional. If you don't want to use this decompiler, skip its installation.

Some of these tools are redundant, but sometimes one fails on a sample while another does not. DroidLysis detects this and tries to switch to a tool that works for the sample.

Example

As of August 13 2020, the following installation works:

$ mkdir softs
$ cd softs
$ wget https://bitbucket.org/iBotPeaches/apktool/downloads/apktool_2.4.1.jar
$ wget https://bitbucket.org/JesusFreke/smali/downloads/baksmali-2.4.0.jar
$ wget https://github.com/pxb1988/dex2jar/files/1867564/dex-tools-2.1-SNAPSHOT.zip
$ unzip dex-tools-2.1-SNAPSHOT.zip

Installation

Once the necessary tools are installed, you have two options:

  1. pip3: recommended install. The package might date back a little, so with this option you might not get the latest version.
  2. clone the repo: this will always be the most up-to-date version.

Easiest install: pip3

The recommended install is with pip3 in a virtual environment (pip3 install virtualenv):

$ python3 -m venv droidlysis
$ cd droidlysis
$ source ./bin/activate
(droidlysis) /droidlysis # pip3 install droidlysis

Most up-to-date solution: clone the repo

Clone the repository: git clone https://github.com/cryptax/droidlysis, then install Python requirements:

$ git clone https://github.com/cryptax/droidlysis
$ cd droidlysis
$ pip3 install -r requirements.txt

Configuration

The configuration is extremely simple, you only need to tune droidconfig.py:

  • APKTOOL_JAR: set the path to your apktool jar
  • BAKSMALI_JAR: set the path to your baksmali jar
  • DEX2JAR_CMD: set the path to the folder containing d2j-dex2.jar.sh. If you did not install dex2jar, simply provide an invalid path here, for example pointing to a non-existant file.
  • PROCYON_JAR: set the path to the procyon decompiler jar. If you don't want Procyon, leave this path to a non existant file.
  • INSTALL_DIR: set the path to your DroidLysis instance. Do not forget to set this or DroidLysis won't work correctly!

Example:

APKTOOL_JAR = os.path.join( os.path.expanduser("~/softs"), "apktool_2.4.1.jar")
BAKSMALI_JAR = os.path.join(os.path.expanduser("~/softs"), "baksmali-2.4.0.jar")
DEX2JAR_CMD = os.path.join(os.path.expanduser("~/softs/dex-tools-2.1-SNAPSHOT"), "d2j-dex2jar.s
h")
PROCYON_JAR = os.path.join( os.path.expanduser("~/softs"), "procyon-decompiler-0.5.36.jar")
INSTALL_DIR = os.path.expanduser("~/droidlysis")

Optionally, if you need a specific situation, you might need to tune the following too. Normally, the default options will work and you won't have to touch these:

  • SQLALCHEMY: specify your SQL database.
  • KEYTOOL: absolute path of keytool which generally ships with Java
  • SMALI_CONFIGFILE: smali patterns
  • WIDE_CONFIGFILE: resource patterns
  • ARM_CONFIGFILE: ARM executable patterns
  • KIT_CONFIGFILE: 3rd party SDK patterns

Usage

DroidLysis has been ported to Python 3. To launch it and get options:

python3 ./droidlysis3.py --help

For example, test it on Signal's APK:

python3 ./droidlysis3.py --input Signal-website-universal-release-4.52.4.apk --output /tmp

DroidLysis outputs:

  • A summary on the console (see example.png)
  • The unzipped, pre-processed sample in a subdirectory of your output dir. The subdirectory is named using the sample's filename and sha256 sum. For example, if we analyze the Signal application and set --output /tmp, the analysis will be written to /tmp/Signalwebsiteuniversalrelease4.52.4.apk-f3c7d5e38df23925dd0b2fe1f44bfa12bac935a6bc8fe3a485a4436d4487a290.
  • A database (by default, SQLite droidlysis.db) containing properties it noticed.

Options

Get usage with python3 ./droidlysis3.py --help

  • The input can be a file or a directory of files to recursively look into. DroidLysis knows how to process Android packages, DEX, ODEX and ARM executables, ZIP, RAR. DroidLysis won't fail on other type of files (unless there is a bug...) but won't be able to understand the content.

  • When processing directories of files, it is typically quite helpful to move processed samples to another location to know what has been processed. This is handled by option --movein. Also, if you are only interested in statistics, you should probably clear the output directory which contains detailed information for each sample: this is option --clearoutput.

  • When dealing with single samples, on the contrary, statistics are typically not so interesting, and their generation can be disabled with --disable-sql

  • DEX decompilation is quite long with Procyon, so this option is disabled by default. If you want to decompile to Java, use --enable-procyon.

  • DroidLysis's analysis does not inspect known 3rd party SDK by default, i.e. for instance it won't report any suspicious activity from these. If you want them to be inspected, use option --no-kit-exception. This usually creates many more detected properties for the sample, as SDKs (e.g. advertisment) use lots of flagged APIs (get GPS location, get IMEI, get IMSI, HTTP POST...).

Sample output directory (--output DIR)

This directory contains (when applicable):

  • A readable AndroidManifest.xml
  • Readable resources in res
  • Libraries lib, assets assets
  • Disassembled Smali code: smali (and others)
  • Package meta information: META-INF
  • Package contents when simply unzipped in ./unzipped
  • DEX executable classes.dex (and others), and converted to jar: classes-dex2jar.jar, and unjarred in ./unjarred

The following files are generated by DroidLysis:

  • autoanalysis.md: lists each pattern DroidLysis detected and where.
  • report.md: same as what was printed on the console

If you do not need the sample output directory to be generated, use the option --clearoutput.

SQLite database

This field is particularly useful when you are processing a directory of samples and later want to scan through properties DroidLysis found in them.

By default, you will find the database in the directory droidlysis.db.

The results are stored in a table named samples. Each entry in the table is relative to a given sample. Each column is properties DroidLysis tracks.

For example, to retrieve all filename, SHA256 sum and smali properties of the database:

sqlite> select sha256, sanitized_basename, smali_properties from samples;
f3c7d5e38df23925dd0b2fe1f44bfa12bac935a6bc8fe3a485a4436d4487a290|Signalwebsiteuniversalrelease4.52.4.apk|{"send_sms": true, "receive_sms": true, "abort_broadcast": true, "call": false, "email": false, "answer_call": false, "end_call": true, "phone_number": false, "intent_chooser": true, "get_accounts": true, "contacts": false, "get_imei": true, "get_external_storage_stage": false, "get_imsi": false, "get_network_operator": false, "get_active_network_info": false, "get_line_number": true, "get_sim_country_iso": true,
...

Property patterns

What DroidLysis detects can be configured and extended in the files of the ./conf directory.

A pattern consist of:

  • a tag name: example send_sms. This is to name the property. Must be unique across the .conf file.
  • a pattern: this is a regexp to be matched. Ex: ;->sendTextMessage|;->sendMultipartTextMessage|SmsManager;->sendDataMessage. In the smali.conf file, this regexp is match on Smali code. In this particular case, there are 3 different ways to send SMS messages from the code: sendTextMessage, sendMultipartTextMessage and sendDataMessage.
  • a description (optional): explains the importance of the property and what it means.
[send_sms]
pattern=;->sendTextMessage|;->sendMultipartTextMessage|SmsManager;->sendDataMessage
description=Sending SMS messages

Updates

v3.3.0 - Dumping data to JSON v3.2.1 - IP address detection v3.2.0 - Dex2jar is optional v3.1.0 - Detection of Base64 strings

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