Gmail exploit may allow attackers to forward e-mail

A Gmail security vulnerability may allow an attacker to set up filters on users' e-mail accounts without their knowledge, according to a proof of concept posted Sunday at

In his post, Brandon writes that the vulnerability has caused some people to lose their domain names registered through

Without posting the full exploit, here is the key as Brandon explains it relies on obtaining the variables that represent the user name and "at":

When you create a filter in your Gmail account, a request is sent to Google's servers to be processed. The request is made in the form of a url with many variables. For security reasons, your browser doesn't display all the variable contained within the url. Using FireFox and a plugin called Live HTTP Headers, you can see exactly what variables are sent from your browser to Google's servers.

After that, an attacker just needs to identify the variable that is the equivalent of the username.

"Obtaining this variable is tricky but possible," he writes. "I'm not going to tell you how to do it, if you search hard enough online you'll find out how."

The "at" variable can be obtained by visiting a malicious Web site, writes Brandon, who suggests that Google make the "at" variable expire after every request rather than after every session.

To avoid being a victim of the vulnerability, users should check their filters often, Brandon suggests. Firefox users can download an extension called NoScript that helps prevent these attacks, he said.

Of course, any Web site that uses cookies for authentication requests can be taken advantage of in the same way. To avoid becoming a victim to this type of exploit, Gmail users should logout of their accounts when they are not in use, and--of course--not visit Web sites that they don't trust.

Google representatives did not immediately return a request for comment.

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