Finding a Way In

By Lisa Vaas Print this article Print

A pervasive vulnerability that allows an attacker to take over any Web browser and silently intercept sensitive data input occurs in Web 2.0 settings from Yahoo to ASP .Net to Google, security firm Fortify says.

One problem with JSON is that CSRF (cross-site request forgery) allows attackers to bypass the technology's cookie-based authentication, as DRW's creator, Walker, says in his blog.

Specifically, CSRF allows a user to invoke cookie-protected actions on a remote server, thus allowing "Mr. Evil to trick Mrs. Innocent into transferring money from her bank account into his," Walker wrote.

Walker is a developer and runs a consultancy called Getahead.

"I believe that JSON is unsafe for anything but public data unless you are using unpredictable URLs," he said in the same blog posting.

Walker said that another, less well-known flaw in JSON is an Array hack that allows malicious users to steal JSON data on Mozilla and any other platform with a modern JavaScript interpreter. This in fact is the subject of Fortify's recent work. Fortify's paper can be downloaded here.

"JSON makes JavaScript Hijacking easier by the fact that a JSON array stands on its own as a valid JavaScript statement. Since arrays are a natural form for communicating lists, they are commonly used wherever an application needs to communicate multiple values. Put another way, a JSON array is directly vulnerable to JavaScript Hijacking. A JSON object is only vulnerable if it is wrapped in some other JavaScript construct that stands on its own as a valid JavaScript statement."

And more details from the Fortify paper:

"Web browsers enforce the Same Origin Policy in order to protect users from malicious Web sites. The Same Origin Policy requires that, in order for JavaScript to access the contents of a Web page, both the JavaScript and the Web page must originate from the same domain. Without the Same Origin Policy, a malicious Web site could serve up JavaScript that loads sensitive information from other Web sites using a client's credentials, culls through it, and communicates it back to the attacker.

"JavaScript Hijacking allows an attacker to bypass the Same Origin Policy in the case that a Web application uses JavaScript to communicate confidential information. The loophole in the Same Origin Policy is that it allows JavaScript from any Web site to be included and executed in the context of any other Web site.

"Even though a malicious site cannot directly examine any data loaded from a vulnerable site on the client, it can still take advantage of this loophole by setting up an environment that allows it to witness the execution of the JavaScript and any relevant side effects it may have. Since many Web 2.0 applications use JavaScript as a data transport mechanism, they are often vulnerable while traditional Web applications are not."

Anywhere this vulnerability can occur, it does occur, Chess said, with the exception of in DWR. As for the major companies behind frameworks, most all said they will work on the vulnerability and that it will be fixed in the next version.

Microsoft, for one, told eWEEK that its MSRC is on this and that the company is investigating new public reports of possible vulnerabilities that occur in applications developed using the downloadable Microsoft ASP.NET AJAX framework.

A Microsoft spokesperson said that the company is not aware of any attacks attempting to use the reported issue or of customer impact at this time. Yahoo had not been able to provide comment by the time this story posted.

Google, for its part, has posted an article that shows developers how to prevent the vulnerabilities described by Fortify in all versions of the Google Web Toolkit.

"We plan to add additional, automatic safeguards in the next version of GWT, due out in the coming weeks, to supplement the security measures developers take on their own," a Google spokesperson added.

These companies have been through the security flaw grinder and know better than to ignore vulnerabilities, Chess said. The problem is that many developers aren't using frameworks from the big players at all—rather, they're rolling their own. Unfortunately, many such developers haven't yet embraced security as their responsibility—and it's this that's prompted Fortify to start banging the drum on the issue.

"Most people don't know when they use these AJAX-style components [i.e., frameworks] that they're at more risk," Chess said. "We need to talk to the AJAX community about what the problem is and what they have to do to address it."

The overwhelming reaction Fortify received from framework maintainers was that this vulnerability is a high-priority fix, Chess said.

What's surprising is the few instances in which framework developers said that security wasn't their problem.

"It makes me really mad to think there are developers out there who are fielding code and who expect people who are going to use that code to figure out all the security ramifications," Chess said.

Chess declined to name names, given that he's still working with them, trying to get recalcitrant developers to address the vulnerability.

In order to make the attack succeed, the browser must be tricked into doing something it wasn't intended to do. In some circumstances, this can be done depending on how JavaScript is formatted.

The Array format is fairly commonly used and makes it easy to trick the browser, Chess said. Exploiting the vulnerability is all about having the conditions necessary to abuse the security policy implemented by a given Web browser. Unfortunately, Fortify found those conditions are fulfilled "a surprising amount of time," he said.

The problem with getting developers to accept responsibility for fixing the vulnerability is easy to spot after comparing AJAX hijacking to, say, buffer overflows, Chess said.

The industry has known about buffer overflows for decades and is usually prompt in addressing them. The problem with JavaScript/AJAX/Web 2.0 security flaws is that there has been no strong message going out to software developers regarding security being their responsibility, Chess said.

"With JavaScript, enterprises are still in the early phases of adopting early programming techniques," he said. "We have an opportunity to get in front of the problem. Before it becomes a widespread" insecure programming practice, he said.

Next Page: How it came to be.

This article was originally published on 2007-04-02
Lisa Vaas is News Editor/Operations for eWEEK.com and also serves as editor of the Database topic center. Since 1995, she has also been a Webcast news show anchorperson and a reporter covering the IT industry. She has focused on customer relationship management technology, IT salaries and careers, effects of the H1-B visa on the technology workforce, wireless technology, security, and, most recently, databases and the technologies that touch upon them. Her articles have appeared in eWEEK's print edition, on eWEEK.com, and in the startup IT magazine PC Connection. Prior to becoming a journalist, Vaas experienced an array of eye-opening careers, including driving a cab in Boston, photographing cranky babies in shopping malls, selling cameras, typography and computer training. She stopped a hair short of finishing an M.A. in English at the University of Massachusetts in Boston. She earned a B.S. in Communications from Emerson College. She runs two open-mic reading series in Boston and currently keeps bees in her home in Mashpee, Mass.
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