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FAQ: Clickjacking -- should you be worried? Nearly all browsers are vulnerable to this new attack class, but details are scarce!

Sep 30, 2008

FAQ: Clickjacking -- should you be worried?

Nearly all browsers are vulnerable to this new attack class, but details are scarce

By Gregg Keizer

September 29, 2008 (Computerworld) Last week, a pair of security researchers spread the news that a new class of vulnerabilities, called "clickjacking," puts users of every major browser at risk from possible attack.

Robert Hansen, founder and chief executive of SecTheory LLC, and Jeremiah Grossman, chief technology officer at WhiteHat Security Inc., spilled some beans last week after they gave a semi-closed presentation at OWASP AppSec 2008 in New York.

Maybe because of the catchy name, or perhaps because it's actually serious stuff, clickjacking got some press. But that still leaves open the question: Just how spooky is it? Are we talking run-for-the-hills scary, or is this just another theoretical attack vector? And what should you do to protect yourself?

We have questions, as usual, and fewer straight answers than we'd like.

What is clickjacking? Good question. Getting to an answer, though, is a little tough, since Hansen and Grossman are keeping virtually all details confidential, at least for now. Here's how Grossman put it to Computerworld last Friday: "Think of any button on any Web site that you can get to appear between the browser walls. Wire transfers on banks, Digg buttons, CPC advertising banners, Netflix queue.... The list is virtually endless, and these are relatively harmless examples. Next, consider that an attack can invisibly hover these buttons below the users' mouse, so that when they click on something they visually see, they actually are clicking on something the attacker wants them to."

In plain English, clickjacking lets hackers and scammers hide malicious stuff under the cover of the content on a legitimate site. You know what happens when a carjacker takes a car? Well, clickjacking is like that, except that the click is the car.

Is clickjacking new? Nope. Not only is it similar to a cross-site request forgery -- a type of vulnerability and attack that has been known since the 1990s -- but Hansen acknowledged that clickjacking goes back several years.

Coincidentally or not, Mozilla last week patched a clickjacking vulnerability in Firefox that was, in turn, a variant of a similar flaw in Internet Explorer that Microsoft first patched in 2003, then patched again in 2004.

How would a clickjacking attack work? We're not sure -- again, because of the paucity of information. But Michal Zalewski, a renowned security researcher who now works for Google, offered up one example.

A malicious page in domain A may create an IFRAME pointing to an application in domain B, to which the user is currently authenticated with cookies," Zalewski said in a message to a mailing list on Thursday. "The top-level page may then cover portions of the IFRAME with other visual elements to seamlessly hide everything but a single UI button in domain B, such as 'delete all items,' 'click to add Bob as a friend,' etc. It may then provide [its] own, misleading UI that implies that the button serves a different purpose and is a part of site A, inviting the user to click it."

In other words, the hacker would dupe users into visiting a malicious page -- through the usual methods -- but then hide the nasty bits under what appears to be the real-deal content from a legitimate site.

How bad is clickjacking? Another good question, but again, the answer's a little dodgy. "Attackers can do quite a lot," Grossman said in a blog post two weeks ago when he and Hansen announced that they had pulled their presentation. "Some things that could be pretty spooky."

Not everyone's convinced that this is a big deal, however. "The difficult thing is finding out what to do with this," said Dave Aitel, CTO at Immunity Inc., in a message to his Dailydave mailing list on Thursday.

In that same vein, there have been few sirens sounded by security teams or organizations. US-CERT, which is under the Department of Homeland Security umbrella, acknowledged the reports but had no new information, and no advice except its standing recommendations for securing a browser.

Speaking of which, what can I do to keep clickjackers back? Not much at the moment. Of the few concrete pieces of advice that have surfaced, one requires giving up the Internet as you know it, while the other will put a serious crimp in your browsing.

The first way to protect yourself from clickjacking is to switch to Lynx, an open-source text-only browser that harks back to the Web's Dark Ages: 1992. Although Lynx is better known in the Unix/Linux world, there are versions for Mac OS X and Windows.

Clickjacking won't work if you're using Lynx, simply because there's no graphic content that an attacker can grab from it to pull over his own malicious code. But text-only browsing is, well, so last century.

Hansen, however, said that the combination of Firefox and NoScript, an extension that blocks JavaScript, Flash and Java content, would keep you safe from "a very good chunk of the issues, 99.99% at this point."

NoScript, which can be downloaded free of charge, has its drawbacks, though: Unless a user manually enables the switch-off-by-default content, many sites will either be unusable or prohibitively limited.

Take note: Giorgio Maone, the creator of NoScript, posted a very interesting entry on his blog Saturday that spells out the add-on's contribution to the clickjacking story. It's well worth reading.

When will the clickjacking problems be patched? That's a toughie.

Hansen had no clue, really -- although he was certain that the only sensible solution is for the browser makers -- Microsoft, Mozilla, Apple, Opera, Google and others -- to build protection into their applications. "The only people who can fix this in a scalable way are the browser vendors," he said.

He and Grossman have connected with Microsoft, Mozilla and Apple so far, companies that together account for more than 98% of the current browser market share. "All are working on solutions," Hansen said, though he's unsure just how high they're prioritizing the problem.

In the meantime, Adobe Systems is working on a fix, reportedly for Flash, although Hansen refused to confirm that last week. It was Adobe that convinced the pair to ditch their planned OWASP AppSec 2008 presentation and delay disclosing their research findings.

When will we know more about clickjacking? Soon. Hansen and Grossman said they will release nearly all of their research, including proof-of-concept code, when Adobe posts its patch.


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