New SSL Web site hack revealed

A researcher has found a convincing way to hack the Secure Sockets Layer (SSL) protocol used to secure log-ins to a range of Web sites, including e-commerce and banking sites.

Using a specially created app, SSLstrip, a researcher calling himself Moxie Marlinspike demonstrated to Black Hat Arlington, Va attendees, how vulnerable many SSL connections were to an involved but clever man-in-the-middle (MitM) attack where a hacker could proxy traffic from users accessing genuine, secure https:// Web site log-ins.

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To prove the usefulness of the attack to a hypothetical criminal, he claimed the hack had given him access to 117 e-mail accounts, 16 credit card numbers, 7 PayPal log-ins, and over 300 other "miscellaneous secure log-ins" in a 24-hour period. Sites involved included Ticketmaster, Paypal, LinkedIn, Hotmail, and Gmail.

The clever bit is that the attack didn't need to touch the encrypted SSL traffic at all, simply exploit the fact that users almost never call HTTPS directly, instead accessing that by calling a conventional HTTP Web page first. That fact makes it possible to monitor and map the traffic between the browser and Web site before the SSL is set up securely, putting itself between the two so that neither site is aware that anything is amiss.

According to Marlinspike, the hack is also able to overcome the possibility that the browser will generate invalid certificate warnings from the fake proxy site, even passing back convincing if bogus favicons such as the traditional HTTPS padlock. The only signal that something is wrong would be the lack of the https:// address in the toolbar, something few users would likely notice, he said.

"Lots of times the security of HTTPS comes down to the security of HTTP, and HTTP is not secure," says Marlinspike in his presentation summary . "If we want to avoid the dialogs of death, start with HTTP not HTTPS."

Importantly, the visual indicators that help ordinary users detect such attacks should once again be emphasized, overturning some years in which developers, including browser developers, had downplayed such reinforcement.

"Once we've got control of that, we can do all kinds of stuff to re-introduce the positive indicators people might miss," he says.

An indirect hack on the secure Web infrastructure was reported some weeks ago, whereby a flaw in the MD5 encryption algorithm was used to fool certificate authorities into accepting a bogus certificate as the real thing.

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