[AOS] Android Frida

FridaLab is an app to study the framework called Frida. Before I knew this app, I kept coming to Crackme’s Android, but it was difficult because I couldn’t understand exactly how to use the API that Frida pursues. My primary purpose of writing this article is to summarize why Frida was used this way.
Let’s get started ~

☝🏻 FridaLab01

Change class challenge_01’s variable ‘chall01’ to 1:

    package uk.rossmarks.fridalab;

    /* loaded from: classes.dex */
    public class challenge_01 {
        static int chall01;

    public static int getChall01Int() {
        return chall01;
        }
    }

The first problem is to access the chall01 variable in challenge_01 class and change the value to 1.
There are three things to think about to solve this problem.

1. How to access the challenge_01 class
   
2. How to approach the challenge_01 variable in the class
   
3. How to approach a variable and put it into the cycle (change)

Let’s work it out step by step

How to access a class

There are two ways to access a particular method through the class.
First, use Java.use(className) API.
The second is to use the Java.choose(className,callback) API.

[ Please refer to the other blog for each description ] -> blog

To access the method

The approach to the method is the same as in any other programming languages. . You can access the class’ methods using the .

To access a variable

Use the ‘value’ field to get the value.

✌🏻 Code

function sol1() {
  console.log("[>] Start");
  //     Java.perform API를 이용하여 가상머신과 연결되어잇는지 확인

  Java.perform(function () {
    // 후킹하고자 하는 변수가 static으로 선언되어 있기 때문에 use
    var className = Java.use("uk.rossmarks.fridalab.challenge_01");

    // 값 접근을 위해 value 사용
    className.chall01.value = 1;

    console.log("[>] 저장된 값: " + className.chall01.value);
  });
}

sol1();