Chrome Extensions & Data Sharing

TL;DR

Yes, Chrome extensions can send data to remote servers. This is how many of them function – for updates, storing settings, or providing features like syncing. However, it also means they could potentially be used maliciously. Understanding how this works helps you choose safe extensions.

How Extensions Send Data

1. Manifest File: Permissions The first place to look is the extension’s manifest file (usually manifest.json). This lists what permissions the extension requests. A key permission to watch for is "permissions": ["storage", "unlimitedStorage"], which allows data storage and retrieval. Also important are network-related permissions like "host_permissions": ["*://*.example.com/*"] or "background": { "scripts": ["background.js"], "service_worker": "service_worker.js" }, which indicate the extension can access websites and make network requests.
   • To find the manifest file: In Chrome, go to chrome://extensions/, enable ‘Developer mode’ (top right). Click ‘Details’ on the extension you want to check. Look for a link to ‘manifest.json’.
2. Network Requests in Code Extensions use JavaScript code to make requests to servers. Common methods include fetch() and XMLHttpRequest.

   const url = 'https://example.com/api/data';
   fetch(url, {
     method: 'POST',
     body: JSON.stringify({ data: 'some information' }),
     headers: { 'Content-Type': 'application/json' }
   })
   .then(response => response.json())
   .then(data => console.log(data));

3. Background Scripts & Service Workers Extensions often use background scripts or service workers to handle tasks even when the extension’s popup isn’t open. These can make network requests independently.

   // In a background script (background.js):
   chrome.runtime.onInstalled.addListener(() => {
     fetch('https://example.com/api/install')
       .then(response => response.json());
   });

4. Storage API The chrome.storage API allows extensions to store data locally in the browser, and potentially sync it with a remote server.

   // Saving data:
   chrome.storage.local.set({ 'key': 'value' }, () => {
     console.log('Data saved');
   });
   
   // Retrieving data:
   chrome.storage.local.get(['key'], (result) => {
     console.log(result.key);
   });

Checking What Data an Extension Sends

1. Chrome Developer Tools: Network Tab Use Chrome’s developer tools to monitor network requests made by the extension.
   • Open Developer Tools (right-click on a webpage, select ‘Inspect’, then go to the ‘Network’ tab).
   • Reload the extension or perform actions within it.
   • Filter requests by the extension’s ID or domain name to see what data is being sent.
2. Privacy Reviews & Extension Permissions Before installing an extension:
   • Read reviews from other users.
   • Carefully examine the permissions it requests – do they seem reasonable for its stated purpose?
   • Check the extension’s privacy policy (if provided).

Protecting Yourself

• Install extensions only from trusted sources (e.g., the Chrome Web Store).
• Keep your Chrome browser updated to benefit from security fixes.
• Regularly review and remove unused or suspicious extensions.