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April 15, 2008

According to various reports, IT security technicians have found a cross-site scripting vulnerability in Google's spreadsheets that opens up the application for potential cookie stealing. Hackers can then use those stolen cookies to illegally gain access to any Google service they may have registered, including their Google Gmail account.

The fact that Google cookies are always valid across all of Google's sub domains makes them even more vulnerable to security breaches. The XSS flaw found on Google's domain exploits the way Internet Explorer distinguishes the content type of the HTTP response being returned by the Web server.

Although other Internet browsers have issues in processing content-type headers properly, this security flaw only applies to Microsoft's Internet Explorer.

The security vulnerability was detected when a technician created a test spreadsheet containing HTML and a string of JavaScript code for viewing a user's cookie. He then saved the spreadsheet and created a link for it to be used as a text-based CSV file, which I.E. mistakenly reads as HTML code.

The security hole has now been patched since it was found yesterday by Internet security researcher, Billy Rios. He expains that the cookie-stealing risk was created by a combination of a caching flaw by Google, and of specific problems in the way some browsers handle content-type headers.

Overall, this is just one of the many XSS flaws Rios has found in Google's Web applications. He published a security advisory last week about a similar vulnerability discovered in Google's code that could potentially allow attackers to steal other users' passwords.

Earlier, Rios said that he also found other flaws in Google's Picasa application.

In other words, people who view a tampered spreadsheet would automatically give their cookie information to a potential attacker. Google says it has since patched that flaw by changing the crafted table content from HTML to simple text.

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Source: Tech Blog.

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