Frida: Question: How to read a JSON file in Javascript code on Android

[waqarrashid33]

Hello everyone,

I want to load the methods that need to be hooked from a JSON file stored on android device. How do I do that?
I tried using the new File(filePath, mode) in the but it says that it can't find the file or directory. I can't make a file either, it gives the error of Read only file system.

The device is rooted and the file path is /data/local/tmp/file.json.

I also tried sending the file using script.post() but I get only half file, may be because of some size limit.
I will appreciate any help. Let me know if you need more info, as I am new to frida and probably missed some needed info.

Cheers.
Waqar

[oleavr]

Hi,

If you want a persistent on-device solution take a look at Gadget's script mode.

The File API doesn't support reading just yet (PR welcome), but for non-trivial agents it's a better idea to use frida-compile anyway and use the frida-fs module.

Cheers!

[waqarrashid33]

Thanks @oleavr . Another question:
But how do I execute the compiled binary? Do I launch it from python bindings just like the JavaScript or some other way?

UPDATE: My bad, so far according to my understanding it generates a single Javascript file from the nodejs project, which can then be loaded using "create_script(fd.read())" in python binding or its counterparts in other bindings.

Waqar

[waqarrashid33]

For those of you who are visiting this issue for similar reason as mine, here is an example script to open a text file on android and send it to host.

'use strict';

const fs = require("frida-fs");

Java.perform(function () {
    var readStream = fs.createReadStream("/path/to/file.txt");
    var text = "";
    readStream
        .on('readable', function () {
            var chunk;
            while (null !== (chunk = readStream.read())) {
                text = text.concat(chunk);
            }
        })
        .on('end', function () {
            send(text);
        });
});

Below are roughly the steps I followed:

To compile this code, first install frida-compile. Thats how I did it:
sudo npm install frida-compile -g

And then create a NodeJS project with npm init in the directory you want your project to be. Then install frida-fs using npm install frida-fs. Then make the app.js( or whatever file you want to use as main script) and paste the above code into it.

Compile this script using frida-compile app.js -o payload.js.
Then change in your binding code, use payload.js as your JavaScript file. e.g in mine it looks like this:
script = process.create_script(open("path/to/payload.js").read())

I hope its helpful.

Waqar