frida-il2cpp-bridge

Frida module to dump, manipulate and hijack any IL2CPP application at runtime with a high level of abstraction.

import Il2Cpp from "frida-il2cpp-bridge";;

async function main() {
    await Il2Cpp.initialize();

    const domain = await Il2Cpp.Domain.get();
    
    const TestAssembly = domain.assemblies["Test.Assembly"].image;
    
    TestAssembly.classes.TestClass.methods.testMethod.intercept({
        onLeave(returnValue) { 
            const testObject = returnValue.value as Il2Cpp.Object;
            testObject.fields.testField.value = 100;
            testObject.methods.newTestMethod.invoke(false, Il2Cpp.String.from("testString"));
        }
    });
    
    TestAssembly.classes.NewTestClass.trace();
}

main().catch(error => console.log(error.stack));

Version support

It should support Unity versions from 5.3.0 to 2021.1.0. I couldn't test them all, please file a bug in case something doesn't work as expected. Thanks to Il2CppInspector for providing the headers.

Platform support

• Linux (not tested)
• Android
• Windows (may need a revision, I just hook LoadLibraryW for now)
• iOS (missing test device and early instrumentation knowledge)

Installation

npm install --save-dev frida-il2cpp-bridge

You may need to include "moduleResolution": "node" in your tsconfig.json.

Snippets

First things first: read the docs.

• Initialization
• Dump
• Print all the strings on the heap
• Find every instance of a certain class
• String manipulation
• Array manipulation
• Class tracing
• Method interception

Initialization

import Il2Cpp from "frida-il2cpp-bridge";;

async function main() {
    await Il2Cpp.initialize();
    const domain = await Il2Cpp.Domain.get();
}

main().catch(error => console.log(error.stack));

Dump

Il2Cpp.dump(domain, `/full/path/to/file.cs`);

This will produce something like:

// mscorlib.dll
class <Module>
{
}

// mscorlib.dll
class Locale : System.Object
{

    static System.String GetText(System.String msg); // 0x01fbb020
    static System.String GetText(System.String fmt, System.Object[] args); // 0x01803a38
}

Find instances

Il2Cpp.choose(YourClass).forEach(instance => {
    // Do whatever you want
});

// Alternatively
Il2Cpp.choose2<Il2Cpp.Array<Il2Cpp.Object>>(YourArrayClass).forEach(instance => {
    // Do whatever you want 2
});

Print all strings

const corlib = domain.assemblies.mscorlib.image;
const StringClass = corlib.classes["System.String"];

Il2Cpp.choose<Il2Cpp.String>(StringClass).forEach(str => {
    console.log(str.handle, str.content);
});

String manipulation

const str = Il2Cpp.String.from("Hello");
console.log(str, str.length); // Hello 5

str.content = "Goodbye";
console.log(str, str.length); // Goodbye 7

Array manipulation

It's not possible to add or remove an array element at the moment.

const corlib = domain.assemblies.mscorlib.image;
const StringClass = corlib.classes["System.String"];

const arr = Il2Cpp.Array.from<Il2Cpp.String>(StringClass, [
    Il2Cpp.String.from("One"), Il2Cpp.String.from("Two"), Il2Cpp.String.from("Three")
]);

console.log(arr.length); // 3
for (const str of arr) {
    console.log(str); // One .. Two .. Three
}

arr.set(0, Il2Cpp.String.from("Zero"));
console.log(arr.get(0)); // Zero

Class tracing

const corlib = domain.assemblies.mscorlib.image;
const StringClass = corlib.classes["System.String"];

StringClass.trace();

It will log something like:

[il2cpp] 0x015ed550 get_Chars
[il2cpp] 0x005602f0 FastAllocateString
[il2cpp] 0x00ab497c wstrcpy
[il2cpp] 0x01a62bc0 IsNullOrEmpty
[il2cpp] 0x015ed550 get_Chars
[il2cpp] 0x015ed550 get_Chars

You can trace single methods as well.

Method interception

You can replace any of the parameters and the return value by reassigning them.

const corlib = domain.assemblies.mscorlib.image;
const StringClass = corlib.classes["System.String"];

StringClass.methods.IsNullOrEmpty.intercept({
    onEnter(instance, parameters) {
        console.log(parameters.value.value);
    },
    onLeave(returnValue) {
        returnValue.value = !(returnValue.value as boolean);
    }
});