AVG Web TuneUp stuffs Chrome security

face palmThe AVG Web TuneUp Chrome extension which it adds to Google Chrome browsers when users were installing the AVG antivirus has a feature which allows attackers to read the user’s browsing history and cookies.

The bug was spotted by Google Project Zero researcher Tavis Ormandy, who worked with AVG for the past two weeks to fix it. Apparently the AVG Web TuneUp extension, which lists over nine million users on its Chrome Web Store page, was vulnerable to trivial XSS (cross-site scripting) attacks.

“This extension adds numerous JavaScript APIs to Chrome, apparently so that they can hijack search settings and the new tab page,” explains Mr. Ormandy. “The installation process is quite complicated so that they [AVG] can bypass the Chrome [Store] malware checks, which specifically tries to stop abuse of the [Chrome] Extension API,” Ormandy said.

Ormandy discovered that many of the custom JavaScript APIs added to Chrome by this extension are responsible for the security issue, being broken or poorly written, allowing attackers access to personal details.

He said that AVG’s developers appear to have forgotten to protect their users against simple cross-domain requests, allowing code hosted on one domain to be executed in the context of another URL.

It would mean that attackers would access to data stored on other websites, such as Gmail, Yahoo, banking websites. All that attackers had to do was to convince a user to access a malicious URL, which is not that tricky.

The extension tiggered HTTPS connections making websites hosted on HTTPS susceptible. For some reason the extension users end up with “SSL disabled.”

VersionĀ  4.2.5.169 of AVG Web TuneUp fixed this issue. In the meantime, Google blocked AVG’s ability to carry out inline installations of this extension. This means that users daft enough to want to install the extension have to go to the Chrome Web Store and trigger the download with a click.