Malicious developers often create extensions that appear legitimate. They might clone the code of a popular open-source extension but add a few lines of malicious keylogging code in the minified JavaScript.
Google has implemented several protections, though determined attackers can bypass some:
Content scripts have limited access to the broader internet due to security restrictions. To bypass this, the captured keystrokes are sent from the content script to the extension's "Background Script" or "Service Worker" using Chrome's internal message passing API ( chrome.runtime.sendMessage ). The background script operates quietly in the background of the browser, independent of any specific open tab. 5. Data Exfiltration keylogger chrome extension work
: Tools like Malwarebytes Browser Guard can detect malicious extension behavior.
Once permissions are granted, the extension utilizes "Content Scripts." These are JavaScript files that the browser automatically injects into the context of the web pages the user loads. Because content scripts run in the context of the web page, they have direct access to the page's Document Object Model (DOM). 3. Event Listening and Interception To bypass this, the captured keystrokes are sent
A does not log "system keys." It logs what you type into the browser . Since 90% of a modern user's sensitive data flows through web forms—login pages, CRMs, banking portals, and chat apps—this limitation is negligible for an attacker.
Manifest.json (v3)
Because keylogger extensions hide in plain sight, you need to be proactive about security.
Recording keystrokes is useless unless the attacker receives them. The extension needs to exfiltrate data. To avoid network monitoring, malicious extensions use several techniques: Data Exfiltration : Tools like Malwarebytes Browser Guard
Tech-savvy users might recognize these as suspicious.
An IT administrator installed a custom "productivity tracker" extension on 500 company Chromebooks. The extension's manifest requested host_permissions for *://*/* . The official Chrome Web Store policy forbids this for private extensions, but the admin forced it via Group Policy. The extension logged every email typed in Gmail and every ticket typed in Zendesk. The data was exfiltrated to a company-owned AWS S3 bucket. This was technically legal (corporate monitoring) but ethically gray.