6 Jun 2007 16:05

eBay's phishy old problem

We were wrong, but is eBay wronger?

Comment Reg Developer recently published a story about listings on eBay that point users to phishing sites. We thought we'd uncovered a new security issue on eBay, but it turns out we were wrong.

Not wrong about the security issue, there certainly is one. Our error was in assuming that it was new and/or that eBay didn't know about it.

Starting from some leads provided by you lot, we have found out that this issue has been well-documented for at least a year.

For example, it is described in a US-CERT vulnerability note dated 02/05/2006, which says: "eBay is a popular auction website. When an eBay user posts an auction, eBay allows SCRIPT tags to be included in the auction description. This creates a cross-site scripting vulnerability in the eBay website."

So the root of the problem is that users are allowed to post active code and active code can be used for malicious purposes.

What can eBay do? Well, if it chose to, it could restrict the HTML that users post to its site. This could have two effects, depending on what restrictions the company enforced: 1) it could ensure that the listing was rendered perfectly safe for other users, or 2) it could restrict the dynamic content that some perfectly legitimate users like to post.

So eBay has to strike a balance between security for its users and the functionality it offers them.

Over a year ago eBay apparently made a conscious decision not to restrict the HTML in this way. In an interview in March 2006, an eBay spokeswoman, Catherine England, is quoted as saying:

"Our sellers really use the dynamic content aspect of our listings. The benefits overwhelmingly outweigh the red skin that we have gotten.

"By the time something gets up there, we're usually so quick to get it and pull it down that it is really a moot point. We feel that it is not a huge concern or issue - it is miniscule."

As we found two weeks ago, "quick" can equate to more than two hours. There is evidence on eBay's own Trust and Safety community board, (here and here), that a malicious listing can stay up for considerably longer than two hours.

These are well worth reading (thanks to Reg Dev reader Lee Berkovits for them). A week may be a long time in politics. On the web even two hours is more than enough time for multiple listings to phish multiple identities.

So, while we agree there is a balance to be struck between security and functionality, we feel eBay has made the wrong decision and is exposing its users to an unacceptable degree of risk. The company, on the other hand, believes this is "not a huge concern or issue - it is miniscule". Ultimately, that is a matter of opinion, so we asked the opinion of a couple of industry experts in the field of security.

Robert Schifreen (security expert and author of Defeating the Hacker) said: "If eBay allows [these] tags within item descriptions, it would appear to me that they understand very little about the basic theory behind writing secure web-based applications.

"One of the golden rules is that you must strip out all html tags from user input, apart from a small subset containing any tags that you specifically want to allow (such as bold or italic text). Allowing users to publish their Javascript programs at will on eBay is asking for trouble, and linking to phishing sites is just the start of it.

"Claiming that it's not a problem because links to phishing sites are quickly removed is, frankly, beyond belief for a high-profile site such as eBay. They should know better."

Nigel Stanley, security practice leader at Bloor Research took no prisoners either. "eBay need a good kick up the backside for allowing such a vulnerability to persist on their site. The very nature of consumer auction sites means that many inexperienced and naïve users will be spending a lot of money on goods believing that they are safe and secure. If this was a two-bit outfit I may give them the benefit of the doubt, but eBay should know better."

So, it isn't just us then.

eBay's reply

We gave eBay the opportunity to reply to our concerns. This is what it said:

"Due to overwhelming demand from the eBay Community, we allow users to use active code in their listing. This enables them to use a number of tools which enhance the content of their listings. A small number of unscrupulous individuals have abused this opportunity to enter malicious code into their listings. In the rare instances where this occurs, it is typically detected by eBay and we've worked swiftly to remove them."

We can see the point, but we think the logic is weak. Of course users want better tools for producing more attractive listings. Whether it be software tools or fairground attractions, people always want bigger, better and faster. That's human nature. But they also have an expectation that the software/attraction will be safe and are justifiably upset when they find out it isn't.