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131 lines
4 KiB
Markdown
131 lines
4 KiB
Markdown
# Frida Tutorial 1
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**From**: [https://medium.com/infosec-adventures/introduction-to-frida-5a3f51595ca1](https://medium.com/infosec-adventures/introduction-to-frida-5a3f51595ca1)
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**APK**: [https://github.com/t0thkr1s/frida-demo/releases](https://github.com/t0thkr1s/frida-demo/releases)
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**Source Code**: [https://github.com/t0thkr1s/frida-demo](https://github.com/t0thkr1s/frida-demo)
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## Python
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Frida allows you to **insert JavaScript code** inside functions of a running application. But you can use **python** to **call** the hooks and even to **interact** with the **hooks**.
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This is a easy python script that you can use with all the proposed examples in this tutorial:
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```python
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#hooking.py
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import frida, sys
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with open(sys.argv[1], 'r') as f:
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jscode = f.read()
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process = frida.get_usb_device().attach('infosecadventures.fridademo')
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script = process.create_script(jscode)
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print('[ * ] Running Frida Demo application')
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script.load()
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sys.stdin.read()
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```
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Call the script:
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```bash
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python hooking.py <hookN.js>
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```
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It is useful to know how to use python with frida, but for this examples you could also call directly Frida using command line frida tools:
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```text
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frida -U --no-pause -l hookN.js -f infosecadventures.fridademo
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```
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## Hook 1 - Boolean Bypass
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Here you can see how to **hook** a **boolean** method \(_checkPin_\) from the class: _infosecadventures.fridademo.utils.PinUtil_
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```javascript
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//hook1.js
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Java.perform(function() {
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console.log("[ * ] Starting implementation override...")
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var MainActivity = Java.use("infosecadventures.fridademo.utils.PinUtil");
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MainActivity.checkPin.implementation = function(pin){
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console.log("[ + ] PIN check successfully bypassed!")
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return true;
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}
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});
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```
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```text
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python hooking.py hook1.js
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```
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Mirar: La funcion recibe como parametro un String, no hace falta overload?
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## Hook 2 - Function Bruteforce
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### Non-Static Function
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If you want to call a non-static function of a class, you **first need a instance** of that class. Then, you can use that instance to call the function.
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To do so, you could **find and existing instance** and use it:
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```javascript
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Java.perform(function() {
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console.log("[ * ] Starting PIN Brute-force, please wait...");
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Java.choose("infosecadventures.fridademo.utils.PinUtil", {
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onMatch: function(instance) {
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console.log("[ * ] Instance found in memory: " + instance);
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for(var i = 1000; i < 9999; i++){
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if(instance.checkPin(i + "") == true){
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console.log("[ + ] Found correct PIN: " + i);
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break;
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}
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}
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},
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onComplete: function() { }
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});
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});
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```
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In this case this is not working as there isn't any instance and the function is Static
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### Static Function
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If the function is static, you could just call it:
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```javascript
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//hook2.js
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Java.perform(function () {
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console.log("[ * ] Starting PIN Brute-force, please wait...")
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var PinUtil = Java.use("infosecadventures.fridademo.utils.PinUtil");
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for(var i=1000; i < 9999; i++)
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{
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if(PinUtil.checkPin(i+"") == true){
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console.log("[ + ] Found correct PIN: " + i);
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}
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}
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});
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```
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## Hook 3 - Retrieving arguments and return value
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You could hook a function and make it **print** the value of the **passed arguments** and the value of the **return value:**
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```javascript
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//hook3.js
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Java.perform(function() {
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console.log("[ * ] Starting implementation override...")
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var EncryptionUtil = Java.use("infosecadventures.fridademo.utils.EncryptionUtil");
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EncryptionUtil.encrypt.implementation = function(key, value){
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console.log("Key: " + key);
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console.log("Value: " + value);
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var encrypted_ret = this.encrypt(key, value); //Call the original function
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console.log("Encrypted value: " + encrypted_ret);
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return encrypted_ret;
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}
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});
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```
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## Important
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In this tutorial you have hooked methods using the name of the mathod and _.implementation_. But if there were **more than one method** with the same name, you will need to **specify the method** that you want to hook **indicating the type of the arguments**.
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You can see that in [the next tutorial](frida-tutorial-2.md).
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