While traditional malicious extensions relied on injecting ads or stealing data, new exploitation techniques are leveraging deeper browser functionalities such as service workers, DOM manipulation, and privilege escalation. These advanced attacks are stealthy, persistent, and harder to detect with standard security tools.
Service Worker Abuse
Service workers are scripts that run in the background of a browser, designed to enable features like offline caching and push notifications. Attackers now use service workers to download malicious payloads dynamically. This allows them to bypass static code reviews, since the harmful logic is retrieved after installation.
Privilege Escalation and Over-Permissioning
Extensions often request powerful privileges such as access to “all sites” or the ability to read/write cookies. Attackers exploit this by inserting malicious code into legitimate extensions or developing new ones that appear harmless. Once granted, these privileges enable session hijacking, cookie theft, and man-in-the-middle style manipulations.
DOM-Based Clickjacking
Another emerging vector involves using transparent overlays and hidden frames within a webpage to trick users into clicking buttons inside extension interfaces. For example, a victim may believe they are closing a pop-up, but in reality, they are granting permissions or approving transactions in an extension such as a password manager or crypto wallet.
Red Flags for Detection
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Service workers making repeated fetch requests to external servers.
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Extensions transmitting authentication cookies or session tokens to unknown domains.
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Invisible UI overlays capturing user interactions.
Defensive Measures
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For developers:
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Minimize permissions and avoid remote code execution.
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Enforce strict Content Security Policies.
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Integrate automated security scanning (e.g., CodeQL) during development.
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For users and enterprises:
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Uninstall unused extensions.
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Regularly audit installed extensions and their permissions.
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Restrict extensions from accessing sensitive websites (such as banking or corporate portals).
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Conclusion
The threat landscape for browser extensions is evolving rapidly. From abusing service workers to executing DOM-based clickjacking, attackers are moving beyond simple malware injection. Developers must follow secure coding practices, while organizations should enforce strict extension management policies,
