LAS VEGAS–A security researcher has found a slew of fundamental problems with the way that modern browsers are designed and built, leading to serious questions about the security of these applications and the way that they handle SSL sessions.
The research, done by Robert Hansen of SecTheory, shows that browsers such as Firefox, Internet Explorer and Chrome have a number of architectural problems that can essentially negate the security that SSL is meant to provide for sensitive Web transactions. The techniques that Hansen has developed, which he demonstrated at the Black Hat conference here Thursday, give an attacker the ability to do any number of nasty things to a target machine, including forcing the download of an executable file, overwriting the URL field in the browser and overwrite secure HTTPS cookies with non-secure cookies.
In all, Hansen found 24 problems before he decided to stop looking. “I had basically had to stop the research because there were just too many issues. I didn’t have time to deal with anymore,” Hansen said.
A big part of the problem, Hansen said in an interview, is that browsers don’t enforce policies that would isolate the tabs in an open browser from one another. This allows an attacker who can control one of the tabs, say a normal non-SSL session, to also affect content in the other tabs, even if they’re using SSL. Hansen identified several techniques that enable him to watch an SSL-protected session and glean a lot of information about what the user is doing, based on timing certain parts of the Web session and knowing how long it takes for part of a site to load. He also can tell whether a user is logged in on a given site and use a specific technique to log the user out so he can then watch the login operation and steal the credentials.
“When you look at it, what does SSL really offer? What this means is that for the average user, against a determined adversary, there really is no protection,” said Hansen, who presented his findings at the Black Hat conference here Thursday. “People give SSL and TLS a lot of credit, when it shouldn’t have any at all.”
SSL is the main transport security used by millions of Web sites to protect data being sent from browsers to Web servers. It’s been shown to be vulnerable to a number of different attacks, including several man-in-the-middle attacks, which could be used in conjunction with some of Hansen’s techniques to completely compromise a supposedly secure Web session.
“The most important thing is that if an attacker can map out the domain ahead of time, he can get a really good feel for how the site is built,” Hansen said. “If there’s a side channel, I can force them to precache some of the content on the page so that I don’t see that again when they reload the page. Then, the only thing you’re seeing are the things that are interesting to the attacker. You can map out the user’s flow around the site and the attacker can force the user to make an SSL connection to them so they can tell which SSL and HTTP headers are being sent in which direction. It’s about narrowing down the number of bytes that are interesting.”
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As troubling as the problems that Hansen found are, he emphasized that they don’t mean that the sky is falling.
“You still need to be a man in the middle first and there are probably easier ways to attack people once you are, but there are a lot of issues here,” he said. “If there was better jitter and padding in SSL, a lof of this wouldn’t even be possible.”
