The researchers found that 27 of the 100 extensions studied contained one or more injection vulnerabilities, for a total of 51 vulnerabilities across all of the extensions. The researchers also said that seven of the vulnerable extensions were used by 300,000 people or more.
"Bugs in extensions put users at risk by leaking private information (like passwords and history) to Web and Wi-Fi attackers," they said. "Websites may be evil or contain malicious content from users or advertisers. Attackers on public Wi-Fi networks (like in coffee shops and airports) can change all HTTP content."
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The researchers sent vulnerability warnings to all relevant developers, and so far two related patches have been released. One involved Twitter's Silver Bird extension (version 220.127.116.11), which had a vulnerability that an attacker could use to hide scripts in the data feed sent to Twitter, although the micro-blogging service appears to sanitize all incoming data against attack. Regardless, the vulnerability was fixed with the release of version 18.104.22.168 of Silver Bird.
Another vulnerability was resolved by Google updating OpenAttribute--used to help people read websites' Creative Commons (CC) licenses--from version 0.6 to 0.7, with the new version locking down the extension's security. According to the Berkeley team's OpenAttribute extension vulnerability disclosure to Google in July, a successful exploit of the vulnerability could allow an attacker to spoof a user's identity when making HTTP requests. In addition, they said, "a malicious website could serve a fake CC license that includes inline scripts, or a Wi-Fi attacker could insert inline scripts into a license provided by a legitimate website like Wikipedia. The inserted code then runs in the extension's popup window with the extension's privileges."
The extension vulnerabilities detailed to date are part of a larger study into Google Chrome security. The full study, to be released in two months, will name and include full details about all of the vulnerable extensions discovered. "We haven't released all of the vulnerable extension names because some of the very popular ones are still unpatched, and we're giving them some time to get fixed," according to a blog post from security researcher Adrienne Porter Felt at Berkeley.
The interest in browser extension security reflects the fact that as browser makers--including Microsoft--have become more adept at securing their code (to say nothing of Microsoft also improving Windows security), attackers have turned their attention to exploiting vulnerabilities in the third-party code--including add-ons and extensions--used by browsers.
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