Frida Tutorial - HackTricks

# Frida Tutorial

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## Installation

Install frida tools:

    pip install frida-tools
    pip install frida

Download and install in the android the frida server (Download the latest release).
One-liner to restart adb in root mode, connect to it, upload frida-server, give exec permissions and run it in backgroud:

    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 &"

Check if it is working:

    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

From: https://medium.com/infosec-adventures/introduction-to-frida-5a3f51595ca1
APK: https://github.com/t0thkr1s/frida-demo/releases
Source Code: https://github.com/t0thkr1s/frida-demo

Follow the link to read it.

### Tutorial 2

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

Follow the link to read it.

### Tutorial 3

From: https://joshspicer.com/android-frida-1
APK: https://github.com/OWASP/owasp-mstg/blob/master/Crackmes/Android/Level_01/UnCrackable-Level1.apk

Follow the link to read it.

You can find more Awesome Frida scripts here: https://codeshare.frida.re/

## Quick Examples

### Calling Frida from command line

    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

    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`

    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()`

    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()`

    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()`

    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:

    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)

    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:

    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
- Part 1 of Advanced Frida Usage blog series: IOS Encryption Libraries

> [!TIP] Learn & practice AWS Hacking:HackTricks Training AWS Red Team Expert (ARTE)
> Learn & practice GCP Hacking: HackTricks Training GCP Red Team Expert (GRTE)

> Support HackTricks
> - Check the subscription plans!
> - Join the 💬 Discord group or the telegram group or follow us on Twitter 🐦 @hacktricks_live.
> - Share hacking tricks by submitting PRs to the HackTricks and HackTricks Cloud github repos.