DecompileApk

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Using Apktool and Frida to do reverse engineering on Android Apk.

DecompileApk 최신버젼 다운로드

최종 버전 다운로드 (.zip)

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# Android Apk reverse engineering using Apktool and Frida

## Table of Content

1. [Environment Setup (macOS mojave)](#Environment-Setup)
2. [Tamper Smali Code](#Tamper-Smali-Code)
3. [Hooking Android Java Methods](#Hooking-Android-Java-Methods)
4. [Hooking Android C Functions](#Hooking-Android-C-Functions)
5. [References](#References)

## [Environment Setup (macOS mojave)](#{name=Environment-Setup})

All the steps mentioned below are on macOS Mojave

### Install Tools on PC

1. Install `frida-tools` with pip3

Run command `$ pip --version` and `$ pip3 --version` to check which *pip* is from at **Python 3x**.  E.g. you should see version information like below:

```bash
    $ pip 19.0.3 from /usr/local/lib/python3.7/site-packages/pip (python 3.7)
    ```

Then run the right **pip** command to install `frida-tools`, e.g.  `pip3`

```bash
    $ pip3 install frida-tools
    ```

Success outputs:

```bash
    ....
    Successfully built frida-tools frida

Installing collected packages: colorama, frida, six, wcwidth, prompt-toolkit, pygments, frida-tools

Successfully installed colorama-0.4.1 frida-12.4.7 frida-tools-1.3.2 prompt-toolkit-2.0.9 pygments-2.3.1 six-1.12.0 wcwidth-0.1.7
    ```

2. Testing your installation

Copy the `cat` binary to a temporary folder, e.g., `/tmp/cat` then run `cat` from that directory:

```bash
    $ mkdir ~/frida
    $ cp /bin/cat /frida/cat
    $ /frida/cat
    ```

In another terminal, make a file `example.py` with the following contents:

```python
    import frida

def on_message(message, data):
        print("[on_message] message:", message, "data:", data)

session = frida.attach("cat")

script = session.create_script("""'use strict';

rpc.exports.enumerateModules = function () {
    return Process.enumerateModulesSync();
    };
    """)
    script.on("message", on_message)
    script.load()

print([m["name"] for m in script.exports.enumerate_modules()])
    ```

Then run the `example.py` script with below command

```bash
    $ python3 example.py
    ```

The output should be something similar to this (depending on your platform and library versions):

```py
    [u'cat', …, u'ld-2.15.so']
    ```

3. Android `adb` command

Make sure  `adb`  can see your device:

```bash
    $ adb devices -l
    ```

This will also ensure that the adb daemon is running on your desktop, which allows Frida to discover and communicate with your device regardless of whether you’ve got it hooked up through USB or WiFi.

### Install `frida-server` on Emulator (or Real Device)

Below steps are based on **Android Emulator Nexus 6P (x86)** api 23 on macOS Majave.

First off, download the latest `frida-server` for Android from  [frida-server releases page](https://github.com/frida/frida/releases), e.g. for Android `x86` emulator, you should download [frida-server-12.4.7-android-x86.xz](https://github.com/frida/frida/releases/download/12.4.7/frida-server-12.4.7-android-x86.xz),  and get it run on your emulator:

```bash
$ adb root # might be required
$ adb push frida-server /data/local/tmp/
$ adb shell "chmod 755 /data/local/tmp/frida-server"
$ adb shell "/data/local/tmp/frida-server &"
```

For the last step, if you see below error:

```bash
Unable to load SELinux policy from the kernel: Failed to open file “/sys/fs/selinux/policy”: Permission denied
```

Then you need to run `frida-server` using the root shell, e.g.

```bash
$ adb shell
angler:/ $ su
angler:/ # /data/local/tmp/frida-server &
[1] 12089
angler:/ #
```

`[1] 12089` is the process id of `frida-server`.

### A quick smoke-test

Now, on your desktop it’s time to make sure the basics are working. Run:

```bash
frida-ps -U
```

This should give you a process list along the lines of:

```bash
  PID  Name
-----  ---------------------------------------------------
  721  ATFWD-daemon
 4450  adbd
  730  android.hardware.biometrics.fingerprint@2.1-service
  407  android.hardware.configstore@1.0-service
  408  android.hardware.graphics.allocator@2.0-service
  409  android.hardware.usb@1.0-service
  410  android.hardware.wifi@1.0-service
  406  android.hidl.allocator@1.0-service
```

## [Tamper Smali Code](#{name=Tamper-Smali-Code})

To tamper a `Boolean` value inside Java source code, i.e. the `Boolean bTamperingSucces = false;`, or some other code you have interest in.

### Tools required

#### apktool

`apktool` can be feteched from [Apktool website](https://ibotpeaches.github.io/Apktool/).  Just follow the steps inside this page to install apktool.

#### adb

`adb` is shipped with Android SDK, it can be found from directory `<your-some-path>/Android/sdk/platform-tools/adb`

#### apksigner

`apksigner` is to sign your apk with a keystore file. This tool can be found at directory `<ANDROID_HOME>/Android/sdk/build-tools/28.0.3/apksigner`, and the usage is documented at [command-line apksigner](https://developer.android.com/studio/command-line/apksigner).

### Steps

1. Clone the example project from [DecompileApk](https://github.com/russell-shizhen/DecompileApk).
2. Find the already compiled apk file `DecompileApk/app/release/app-release.apk`.
3. Decompile it using **apktool**.

```bash
    $ cd <your-path>/DecompileApk/app/release/
    $ apktool d --no-res -f app-release.apk
    ```

You will see below outputs

```bash
    I: Using Apktool 2.4.0 on app-release.apk
    I: Copying raw resources...
    I: Baksmaling classes.dex...
    I: Copying assets and libs...
    I: Copying unknown files...
    I: Copying original files...
    ```

4. Look for `DecompileApk/app/release/app-release/smali/com/arophix/decompileapk/MainActivity.smali` under the smali code directory and find below code

```c
    const/4 p1, 0x0
    ```

5. Just change `0x0` (meaning `false`) to `0x1` (meaning `true`)  and save the file.

6. Using **apktool** to build the tampered apk.

```c
    apktool b app-release
    ```

You should see below outputs

```bash
    I: Using Apktool 2.4.0
    I: Checking whether sources has changed...
    I: Smaling smali folder into classes.dex...
    I: Checking whether resources has changed...
    I: Copying raw resources...
    I: Copying libs... (/lib)
    I: Building apk file...
    I: Copying unknown files/dir...
    I: Built apk...
    ```

7. Find the newly built apk from `dist` directory `DecompileApk/app/release/app-release/dist/app-release.apk`

8. Sign the apk using **apksigner** and keystore located at `DecompileApk/app/decompileapk.jks` (please modify the paths for keystore and apk per your own case accordingly),

```bash
   $ <ANDROID_HOME>/sdk/build-tools/28.0.3/apksigner sign --ks ../decompileapk.jks app-release.apk
   ```

You should see below outputs and enter the password `123456`

```bash
   Keystore password for signer #1:
   ```

9. Install the signed apk using adb command.

```bash
    $ adb install <path-to-the-tampered-apk>/app-release.apk
    ```

10. Instead of seeing `"Hello from C++"` from the screen, you should now see `"Hello, Android reverse engineer!"`.

## [Hooking Android Java Methods](#{name=Hooking-Android-Java-Methods})

Hooking Android Java source code using Frida.

Find the script from [hook_java_methods.py](https://github.com/russell-shizhen/DecompileApk/blob/master/scripts/hook_java_methods.py) and run it using below command, and then click on the button of your started Android app.

```bash
$ python3 hook_java_methods.py

[*] Running CTF
[*] onClick
[*] Called - isPhoneRooted()
[*] onClick
[*] Called - isPhoneRooted()
```

If you see an error like below:

```bash
$ frida.ServerNotRunningError: unable to connect to remote frida-server: closed
```

Remember that you have started `frida-server` on your emulator.

Meanwhile, on your emulator screen, you shoud see the toast message changed to `Device not rooted` if success.

## [Hooking Android C Functions](#{name=Hooking-Android-C-Functions})

Hooking Android C source code using Frida.

1. Decompile APK

Firstly, decompile the apk using apktool to extract the shared library, i.e. `libnative-lib.so`.

```bash
    $ cd DecompileApk/app/release
    $ apktool d --no-res app-release.apk
    ```

2. Find the target JNI method

Secondly, use below command to find the JNI function to hook.

```bash
    $ nm --demangle --dynamic app-release/lib/x86/libnative-lib.so
    ```

You should see below outputs:

```bash
    00004d80 T Java_com_arophix_decompileapk_MainActivity_stringFromJNI
    000090b0 T std::bad_typeid::what() const
    00005cf0 T std::bad_exception::what() const
    00005e70 T std::bad_array_length::what() const
    00005df0 T std::bad_array_new_length::what() const
    00008ff0 T std::bad_cast::what() const
    ...
    ```

3. Hook C function by name

Find the script from [hooknative-by-function-name.py](https://github.com/russell-shizhen/DecompileApk/blob/master/scripts/hooknative-by-function-name.py) and run it using below command, and then click on the button of your started Android app.

```bash
    $ python3 hooknative-by-function-name.py

[*] Running Arophix Hook Test ...
    Java_com_arophix_decompileapk_MainActivity_stringFromJNI called with:
    ret: 0x200019
    ```

If you see an error like below:

```bash
    $ frida.ServerNotRunningError: unable to connect to remote frida-server: closed
    ```

Remember that you have started `frida-server` on your emulator.

Meanwhile, on your emulator screen, you shoud see the text changed to `Frida is hooking this displayed text from Native layer by function name.` if success.

4. Hook C function by address

Find the script from [hooknative-by-function-address.py](https://github.com/russell-shizhen/DecompileApk/blob/master/scripts/hooknative-by-function-address.py) and run it using below command, and then click on the button of your started Android app.

```bash
    $ python3 hooknative-by-function-address.py

[*] Running Arophix Hook Test ...
    [+] membase: 0xb2acd000
    [+] addressOfStringFromJni: 0xb2ad1d80
    [++] addressOfStringFromJni: 0xb2ad1d80
    ret: 0x19
    ```

If you see an error like below:

```bash
    $ frida.ServerNotRunningError: unable to connect to remote frida-server: closed
    ```

Remember that you have started `frida-server` on your emulator.

Meanwhile, on your emulator screen, you shoud see the text changed to `Frida is hooking this displayed text from Native layer by function address.` if success.

## [References](#{name=References})

- [https://www.frida.re/docs/android/](https://www.frida.re/docs/android/)
- [https://www.frida.re/docs/examples/android/](https://www.frida.re/docs/examples/android/)
- [https://11x256.github.io/Frida-hooking-android-part-1/](https://11x256.github.io/Frida-hooking-android-part-1/)
- [https://github.com/antojoseph/frida-android-hooks/blob/master/hooking-native-code.py](https://github.com/antojoseph/frida-android-hooks/blob/master/hooking-native-code.py) 
- [https://awakened1712.github.io/hacking/hacking-frida/](https://awakened1712.github.io/hacking/hacking-frida/)
- [https://awakened1712.github.io/hacking/hacking-frida/#c-hook-a-static-function-by-resolving-its-address](https://awakened1712.github.io/hacking/hacking-frida/#c-hook-a-static-function-by-resolving-its-address)
- [https://stackoverflow.com/questions/51811348/find-manually-registered-obfuscated-native-function-address](https://stackoverflow.com/questions/51811348/find-manually-registered-obfuscated-native-function-address)

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