Electron is **based on Chromium**, but it is not a browser. Certain principles and security mechanisms implemented by modern browsers are not in place.
A **renderer process** will be a browser window loading a file:
```javascript
const {BrowserWindow} = require('electron');
let win = new BrowserWindow();
//Open Renderer Process
win.loadURL(`file://path/to/index.html`);
```
Settings of the **renderer process** can be **configured** in the **main process** inside the main.js file. Some of the configurations will **prevent the Electron application to get RCE** or other vulnerabilities if the **settings are correctly configured**.
The desktop application might have access to the user’s device through Node APIs. The following two configurations are responsible for providing mechanisms to **prevent the application JavaScript from having direct access to the user’s device** and system level commands.
* **`nodeIntegration`** - is `off` by default. If on, allows to access node features from the renderer process.
* **`contextIsolation`** - is `on` by default. If on, main and renderer processes aren't isolated.
If the **nodeIntegration** is set to **on**, a web page's JavaScript can use Node.js features easily just by calling the `require()`. For example, the way to execute the calc application on Windows is:
```html
<script>
require('child_process').exec('calc');
</script>
```
## RCE: preload
The script indicated in this setting is l**oaded before other scripts in the renderer**, so it has **unlimited access to Node APIs**:
Therefore, the script can export node-features to pages:
{% code title="preload.js" %}
```javascript
typeof require === 'function';
window.runCalc = function(){
require('child_process').exec('calc')
};
```
{% endcode %}
{% code title="index.html" %}
```html
<body>
<script>
typeof require === 'undefined';
runCalc();
</script>
</body>
```
{% endcode %}
{% hint style="info" %}
**If `contextIsolation` is on, this won't work**
{% endhint %}
## RCE: XSS + contextIsolation
The _**contextIsolation**_ introduces the **separated contexts between the web page scripts and the JavaScript Electron's internal code** so that the JavaScript execution of each code does not affect each. This is a necessary feature to eliminate the possibility of RCE.
If the contexts aren't isolated an attacker can:
1. Execute **arbitrary JavaScript in renderer** (XSS or navigation to external sites)
2.**Overwrite the built-in method** which is used in preload or Electron internal code to own function
If `contextIsolation` set to false you can try to use \<webview> (similar to \<iframe> but can load local files) to read local files and exfiltrate them: using something like **\<webview src=”file:///etc/passwd”>\</webview>:**
Supposing you found a XSS but you **cannot trigger RCE or steal internal files** you could try to use it to **steal credentials via phishing**.
First of all you need to know what happen when you try to open a new URL, checking the JS code in the front-end:
```javascript
webContents.on("new-window", function (event, url, disposition, options) {} // opens the custom openInternally function (it is declared below)
webContents.on("will-navigate", function (event, url) {} // opens the custom openInternally function (it is declared below)
```
The call to **`openInternally`** will decide if the **link** will be **opened** in the **desktop window** as it's a link belonging to the platform, **or** if will be opened in the **browser as a 3rd party resource**.
In the case the **regex** used by the function is **vulnerable to bypasses** (for example by **not escaping the dots of subdomains**) an attacker could abuse the XSS to **open a new window which** will be located in the attackers infrastructure **asking for credentials** to the user:
* [**Electronegativity**](https://github.com/doyensec/electronegativity) is a tool to identify misconfigurations and security anti-patterns in Electron-based applications.
* [**Electrolint**](https://github.com/ksdmitrieva/electrolint) **** is an open source VS Code plugin for Electron applications that uses Electronegativity.
* More researches and write-ups about Electron security in [https://github.com/doyensec/awesome-electronjs-hacking](https://github.com/doyensec/awesome-electronjs-hacking)
