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Researchers poke holes in super duper SSL

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Websites that use an enhanced form of digital authentication remain just as vulnerable to a common form of spoofing attack as those that use less costly certificates, two researchers have found.

Previously, so-called extended validation secure sockets layer certificates (or EV SSL) were believed to be immune to man-in-the-middle attacks, in which an interloper on a hotel network or Wi-Fi hotspot sits between an end user and the site she is visiting. When researchers demonstrated one such attack in December, SSL issuers proudly proclaimed that the more expensive EV certs were impervious to the technique.

Independent researchers Alexander Sotirov and Mike Zusman have now proven that assumption wrong. Because of design flaws in most browsers, it's possible to perform a MITM attack and still cause the browser's address bar to display a green bar indicating the site is protected by EV SSL. The researchers presented their findings last week at the CanSecWest security conference in Vancouver.

The attack method still requires that an attacker obtain a fraudulent SSL certificate, but that's certainly not outside the realm of possibility. Zusman and others have already shown it's possible to obtain a no-questions-asked SSL certificate for Mozilla.com. Zusman was also successful in obtaining an SSL certificate for Microsoft's login.live.com domain.

Once the fraudulent certificate is appropriated, the attacker allows the victim to reach the legitimate EV-protected site. The attacker then uses the plain-vanilla cert to inject javascript or other content into the legitimate page. Because most browsers are unable to distinguish between the two types of SSL, the green bar continues to be displayed.

"Once we can inject javascript into the page, we have full control over the page," Sotirov told The Reg. "We can modify it, we can intercept the data that's being submitted when the user clicks the login button. We can intercept keystrokes on that page."

Sotirov said he still believes EV certs are valuable because they require additional vetting of the applicant's identity. That's a considerable improvement over the current SSL infrastructure, in which some 135 certificate authorities exercise varying procedures for deciding whether to issue someone an SSL credential.

But until browser makers figure out how to distinguish between the two types of certificates, there can be no guarantees that the little green button in your address bar really means no one has tampered with the site you're visiting. And making that happen without breaking website compatibility won't be easy.

"For a lot of sites, it's hard not to have mixed content," Sotirov said. "Google Analytics and other third party content providers might not have extended validation. Suddenly, all those sites break." ®

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