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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​

Follow the link to read it.

​Tutorial 2​

Follow the link to read it.​

​Tutorial 3​

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

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Learn AWS hacking from zero to hero with htARTE (HackTricks AWS Red Team Expert)!
Other ways to support HackTricks: