Original URL: http://www.theregister.co.uk/2008/02/01/google_ssl_sidejacking/

Et tu, Gmail? Simple hack defeats last barrier to decades-old attack

Only Salesforce standing

By Dan Goodin

Posted in Security, 1st February 2008 02:13 GMT

In the morass of Web 2.0 insecurity, Gmail and other Google-hosted services stood out as a beacon of hope. That's because they were believed to be the only free destination that offered protection against a decade-old vulnerability that enabled hackers to steal sensitive authentication details as they pass over Wi-Fi hotspots and other types of public networks.

Now, we know better.

According to security researcher Rob Graham, it doesn't take much to disable the safety measure. And that, in turn, would give attackers free rein over a victim's Google account, including any email, map searches or calendar entries that happen to be housed there.

The vulnerability stems from the wide-spread use of session-IDs that websites use after visitors have successfully entered their login credentials. Typically, they come in the form of random text strings in the URL or the HTTP cookie and are sent in the clear.

That makes it a snap for bad guys hanging out at coffee shops to sniff the string and use it to masquerade as the victim. This happens even if the password is entered behind the veil of a Secure Socket Layer session, which encrypts the information so it's not decipherable to prying eyes.

Google was the only free service known to encrypt the session-ID if the user went through the trouble of putting an HTTPS in the address for Gmail and other Google services that support SSL. Visit this Google Calendar address instead of this one and no one would be able to make heads or tails of the session-ID, the thinking went.

But Graham says Google SSL will automatically revert to plain-vanilla HTML if the site believes there are connection problems. This means an attacker at a hotspot can cause Google to lower its shield simply by sending a reset packet to either the Google server or to the victim's PC.

"If companies do SSL correctly, then you're safe," Graham says. "The problem with Gmail is it's not doing SSL correctly. In my experience just using Gmail normally, I've seen this happen accidentally."

A Google spokeswoman said company security pros were looking in to Graham's research.

Graham posted his finding here more than two weeks ago. It remained largely overlooked until George Ou picked it up on the Zero Day Blog.

To be fair, Google still offers protections that Yahoo!, MySpace, Facebook and most other Web 2.0 properties do not. That's because Gmail and several other Google services that support SSL encrypt all information passed back and forth during a session. Most other websites encrypt data only during the login sequence and then quickly drop the protection once the user has been authenticated.

Among websites Graham has tested, only Salesforce.com has managed to insulate itself from this man-in-the-middle attack.

"As far as I can tell, they really have spent a lot of effort to solve problems like this," he says. ®