【Android 逆向】【攻防世界】ill-intentions

1. apk 安装到手机， 啥输入框都没有

2. apk拖入到jadx中看看

public class MainActivity extends Activity {
    @Override // android.app.Activity
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        TextView tv = new TextView(getApplicationContext());
        tv.setText("Select the activity you wish to interact with.To-Do: Add buttons to select activity, for now use Send_to_Activity");
        setContentView(tv);
        IntentFilter filter = new IntentFilter();
        filter.addAction("com.ctf.INCOMING_INTENT");
        Send_to_Activity receiver = new Send_to_Activity();
        registerReceiver(receiver, filter, Manifest.permission._MSG, null);
    }
}

大概就是动态注册了一个广播接收器，看看接收器代码

/* loaded from: classes.dex */
public class Send_to_Activity extends BroadcastReceiver {
    @Override // android.content.BroadcastReceiver
    public void onReceive(Context context, Intent intent) {
        String msgText = intent.getStringExtra("msg");
        if (msgText.equalsIgnoreCase("ThisIsTheRealOne")) {
            Intent outIntent = new Intent(context, ThisIsTheRealOne.class);
            context.startActivity(outIntent);
        } else if (msgText.equalsIgnoreCase("IsThisTheRealOne")) {
            Intent outIntent2 = new Intent(context, IsThisTheRealOne.class);
            context.startActivity(outIntent2);
        } else if (msgText.equalsIgnoreCase("DefinitelyNotThisOne")) {
            Intent outIntent3 = new Intent(context, DefinitelyNotThisOne.class);
            context.startActivity(outIntent3);
        } else {
            Toast.makeText(context, "Which Activity do you wish to interact with?", 1).show();
        }
    }
}

广播接收就跳转到各个activity，直接使用objecttion来实现直接跳到对应的activity

└─# objection -g com.example.hellojni explore

                                                                                                          
A newer version of objection is available!                                                                
You have v1.9.6 and v1.11.0 is ready for download.
                                                                                                          
Upgrade with: pip3 install objection --upgrade
For more information, please see: https://github.com/sensepost/objection/wiki/Updating

Using USB device `MI 5X`
Agent injected and responds ok!

     _   _         _   _
 ___| |_|_|___ ___| |_|_|___ ___
| . | . | | -_|  _|  _| | . |   |
|___|___| |___|___|_| |_|___|_|_|
      |___|(object)inject(ion) v1.9.6

     Runtime Mobile Exploration
        by: @leonjza from @sensepost

[tab] for command suggestions
com.example.hellojni on (xiaomi: 8.1.0) [usb] # android intent launch_activity com.example.application.Def
initelyNotThisOne
 
(agent) Starting activity com.example.application.DefinitelyNotThisOne...
(agent) Activity successfully asked to start.
com.example.hellojni on (xiaomi: 8.1.0) [usb] # android intent launch_activity com.example.application.IsT
hisTheRealOne
(agent) Starting activity com.example.application.IsThisTheRealOne...
(agent) Activity successfully asked to start.
com.example.hellojni on (xiaomi: 8.1.0) [usb] # 

每个activity 都使用了一个native函数， hook住它，看看有没有什么发现

3. 编写脚本

function main() {
Java.perform(function() {
    var DefinitelyNotThisOneHandler = Java.use('com.example.application.DefinitelyNotThisOne')
    DefinitelyNotThisOneHandler.definitelyNotThis.implementation = function(arg0, arg1) {
        console.log('DefinitelyNotThisOneHandler called: ' + arg0 + "  \n" + arg1)
        var ret = this.definitelyNotThis(arg0, arg1)
        console.log('DefinitelyNotThisOneHandler ret: ' + ret )
        return ret
    }

    var ThisIsTheRealOneHandler = Java.use('com.example.application.ThisIsTheRealOne')
    ThisIsTheRealOneHandler.orThat.overload('java.lang.String', 'java.lang.String', 'java.lang.String').implementation = function(arg0, arg1, arg2) {
        console.log('ThisIsTheRealOneHandler called: ' + arg0 + "  \n" + arg1 + "  \n" + arg2)
        var ret =  this.orThat(arg0, arg1, arg2)
        console.log('ThisIsTheRealOneHandler ret: ' + ret )
        return ret
    }

    var IsThisTheRealOneHandler = Java.use('com.example.application.IsThisTheRealOne')
    IsThisTheRealOneHandler.perhapsThis.overload('java.lang.String', 'java.lang.String', 'java.lang.String').implementation = function(arg0, arg1, arg2) {
        console.log('IsThisTheRealOneHandler called: ' + arg0 + "  \n" + arg1 + "  \n" + arg2)
        var ret =  this.perhapsThis(arg0, arg1, arg2)
        console.log('IsThisTheRealOneHandler ret: ' + ret )
        return ret
    }
})
}

setImmediate(main)

日志

(hooker_3.8.5) ┌──(hooker_3.8.5)(root㉿r0env)-[~/Documents/code_dir/study/20230215/001]
└─# frida -U com.example.hellojni -l lesson16.js --no-pause
     ____
    / _  |   Frida 14.2.2 - A world-class dynamic instrumentation toolkit
   | (_| |
    > _  |   Commands:
   /_/ |_|       help      -> Displays the help system
   . . . .       object?   -> Display information about 'object'
   . . . .       exit/quit -> Exit
   . . . .
   . . . .   More info at https://www.frida.re/docs/home/
                                                                                
[MI 5X::com.example.hellojni]-> DefinitelyNotThisOneHandler called: YjYwYWZjMjRkMhVhZTQhZDIwZGFkNWJhMGZmZGYiYmQaMmFkMjBiMTEhNDAtMzMzMjdlZmEWNzU?
  
MzYwNjMeNjgxNWZkNGQeOTFhOTIhNDkiMDVhNDBkYTAyNWQtYhYxNWYwOTUxMzZiMTlmMzciMjM?

DefinitelyNotThisOneHandler ret: Told you so!
[MI 5X::com.example.hellojni]->
[MI 5X::com.example.hellojni]->
[MI 5X::com.example.hellojni]->
[MI 5X::com.example.hellojni]-> IsThisTheRealOneHandler called: TRytfrgooq|F{i-JovFBungFk\VlphgQbwvj~HuDgaeTzuSt.@Lex^~  
ZGFkNGIwYzIWYjEzMTUWNjVjNTVlNjZhOGJkNhYtODIyOGEaMTMWNmQaOTVjZjkhMzRjYmUzZGE?
  
MzQxZTZmZjAxMmIiMWUzNjUxMmRiYjIxNDUwYTUxMWItZGQzNWUtMzkyOWYyMmQeYjZmMzEaNDQ?

IsThisTheRealOneHandler ret: Congratulation!YouFoundTheRightActivityHereYouGo-CTF{IDontHaveABadjokeSorry}

日志中（返回值）发现flag