A piece that was authored last September, enumerating some of the security issues with Google Chrome Extensions. The authors:
reviewed 100 Chrome extensions and found that 27 of the 100 extensions leak all of their privileges to a web or WiFi attacker. Bugs in extensions put users at risk by leaking private information (like passwords and history) to web and WiFi attackers. Web sites may be evil or contain malicious content from users or advertisers. Attackers on public WiFi networks (like in coffee shops and airports) can change all HTTP content. We’ll show you how you can prevent attacks on your extension using Content Security Policy.
Check out the article, and some of the other great pieces that they’ve published on security.