# Frida Tutorial

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## Installation

Install **frida tools**:

```bash
pip install frida-tools
pip install frida
```

**Download and install** in the android the **frida server** ([Download the latest release](https://github.com/frida/frida/releases)).\
One-liner to restart adb in root mode, connect to it, upload frida-server, give exec permissions and run it in backgroud:

{% code overflow="wrap" %}
```bash
adb root; adb connect localhost:6000; sleep 1; adb push frida-server /data/local/tmp/; adb shell "chmod 755 /data/local/tmp/frida-server"; adb shell "/data/local/tmp/frida-server &" 
```
{% endcode %}

**Check** if it is **working**:

```bash
frida-ps -U #List packages and processes
frida-ps -U | grep -i <part_of_the_package_name> #Get all the package name
```

## Tutorials

### [Tutorial 1](frida-tutorial-1.md)

**From**: [https://medium.com/infosec-adventures/introduction-to-frida-5a3f51595ca1](https://medium.com/infosec-adventures/introduction-to-frida-5a3f51595ca1)\
**APK**: [https://github.com/t0thkr1s/frida-demo/releases](https://github.com/t0thkr1s/frida-demo/releases)\
**Source Code**: [https://github.com/t0thkr1s/frida-demo](https://github.com/t0thkr1s/frida-demo)

**Follow the [link to read it](frida-tutorial-1.md).**

### [Tutorial 2](frida-tutorial-2.md)

**From**: [https://11x256.github.io/Frida-hooking-android-part-2/](https://11x256.github.io/Frida-hooking-android-part-2/) (Parts 2, 3 & 4)\
**APKs and Source code**: [https://github.com/11x256/frida-android-examples](https://github.com/11x256/frida-android-examples)

**Follow the[ link to read it.](frida-tutorial-2.md)**

### [Tutorial 3](owaspuncrackable-1.md)

**From**: [https://joshspicer.com/android-frida-1](https://joshspicer.com/android-frida-1)\
**APK**: [https://github.com/OWASP/owasp-mstg/blob/master/Crackmes/Android/Level\_01/UnCrackable-Level1.apk](https://github.com/OWASP/owasp-mstg/blob/master/Crackmes/Android/Level\_01/UnCrackable-Level1.apk)

**Follow the [link to read it](owaspuncrackable-1.md).**

**You can find more Awesome Frida scripts here:** [**https://codeshare.frida.re/**](https://codeshare.frida.re)

## Quick Examples

### Calling Frida from command line

```bash
frida-ps -U

#Basic frida hooking
frida -l disableRoot.js -f owasp.mstg.uncrackable1

#Hooking before starting the app
frida -U --no-pause -l disableRoot.js -f owasp.mstg.uncrackable1
#The --no-pause and -f options allow the app to be spawned automatically,
#frozen so that the instrumentation can occur, and the automatically
#continue execution with our modified code.
```

### Basic Python Script

```python
import frida, sys

jscode = open(sys.argv[0]).read()
process = frida.get_usb_device().attach('infosecadventures.fridademo')
script = process.create_script(jscode)
print('[ * ] Running Frida Demo application')
script.load()
sys.stdin.read()
```

### Hooking functions without parameters

Hook the function `a()` of the class `sg.vantagepoint.a.c`

```javascript
Java.perform(function () {
;  rootcheck1.a.overload().implementation = function() {
  rootcheck1.a.overload().implementation = function() {
    send("sg.vantagepoint.a.c.a()Z   Root check 1 HIT!  su.exists()");
    return false;
  };
});
```

Hook java `exit()`

```javascript
var sysexit = Java.use("java.lang.System");
  sysexit.exit.overload("int").implementation = function(var_0) {
    send("java.lang.System.exit(I)V  // We avoid exiting the application  :)");
  };
```

Hook MainActivity `.onStart()` & `.onCreate()`

```javascript
var mainactivity = Java.use("sg.vantagepoint.uncrackable1.MainActivity");
  mainactivity.onStart.overload().implementation = function() {
    send("MainActivity.onStart() HIT!!!");
    var ret = this.onStart.overload().call(this);
  };
  mainactivity.onCreate.overload("android.os.Bundle").implementation = function(var_0) {
    send("MainActivity.onCreate() HIT!!!");
    var ret = this.onCreate.overload("android.os.Bundle").call(this,var_0);
  };
```

Hook android `.onCreate()`

```javascript
  var activity = Java.use("android.app.Activity");
  activity.onCreate.overload("android.os.Bundle").implementation = function(var_0) {
    send("Activity HIT!!!");
    var ret = this.onCreate.overload("android.os.Bundle").call(this,var_0);
  };
```

### Hooking functions with parameters and retrieving the value

Hooking a decryption function. Print the input, call the original function decrypt the input and finally, print the plain data:

```javascript
  function getString(data){
      var ret = "";
      for (var i=0; i < data.length; i++){
          ret += data[i].toString();
        }
      return ret
    } 
  var aes_decrypt = Java.use("sg.vantagepoint.a.a");
  aes_decrypt.a.overload("[B","[B").implementation = function(var_0,var_1) {
    send("sg.vantagepoint.a.a.a([B[B)[B   doFinal(enc)  // AES/ECB/PKCS7Padding");
    send("Key       : " + getString(var_0));
    send("Encrypted : " + getString(var_1));
    var ret = this.a.overload("[B","[B").call(this,var_0,var_1);
    send("Decrypted : " + ret);

    var flag = "";
    for (var i=0; i < ret.length; i++){
      flag += String.fromCharCode(ret[i]);
    }
    send("Decrypted flag: " + flag);
    return ret; //[B
  };
```

### Hooking functions and calling them with our input

Hook a function that receives a string and call it with other string (from [here](https://11x256.github.io/Frida-hooking-android-part-2/))

```javascript
var string_class = Java.use("java.lang.String"); // get a JS wrapper for java's String class

my_class.fun.overload("java.lang.String").implementation = function(x){ //hooking the new function
  var my_string = string_class.$new("My TeSt String#####"); //creating a new String by using `new` operator 
  console.log("Original arg: " +x );
  var ret =  this.fun(my_string); // calling the original function with the new String, and putting its return value in ret variable
  console.log("Return value: "+ret);
  return ret;
};
```

### Getting an already created object of a class

If you want to extract some attribute of a created object you can use this.

In this example you are going to see how to get the object of the class my\_activity and how to call the function .secret() that will print a private attribute of the object:

```javascript
Java.choose("com.example.a11x256.frida_test.my_activity" , {
  onMatch : function(instance){ //This function will be called for every instance found by frida
    console.log("Found instance: "+instance);
    console.log("Result of secret func: " + instance.secret());
  },
  onComplete:function(){}
});
```

## Other Frida tutorials

* [https://github.com/DERE-ad2001/Frida-Labs](https://github.com/DERE-ad2001/Frida-Labs)
* [Part 1 of Advanced Frida Usage blog series: IOS Encryption Libraries](https://8ksec.io/advanced-frida-usage-part-1-ios-encryption-libraries-8ksec-blogs/)



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