eBay has resolved a cross-site scripting bug on its website that independent experts warned posed a significant risk of fraud to users of the auction site. The XSS flaw meant that, once logged into a seller account on eBay, an attacker could insert an XSS exploit code into a listing of an item for sale.
The XSS security flaw on eBay.com, discovered by Indian security researcher Shubham Upadhyay last week, created a means for hackers to inject attack code as "user-submitted content" in product listings. According to XSSed, the script insertion vulnerability provided a means to fling browser exploits and other nasties at surfers who viewed booby-trapped auctions.
And an independent security expert reckoned the vulnerability might even have lent itself to tricking victims into placing bids on auction items without their consent.
In a statement issued today, an eBay spokeswoman confirmed that the bug had been quashed and outlined eBay's general approach to automatically scanning for XSS-related vulnerabilities on the online marketplace.
We were aware of this case and the issue has already been dealt with.
eBay has a tool that scans for such XSS vulnerabilities in user generated content. Like any automated tools, false positives and negatives do occur. Once we determine the user has violated eBay policy, we immediately remove the item and suspend the user account.
Scanning for cross-site scripting nasties is just one of the tools "numerous security detection tools" eBay applies in its ongoing fight to ensure the safety and security of our marketplace, she added. eBay said around 60 million items are listed on its UK site alone at any one time, with more than 17 million people visiting the site each month.
Dominique Karg, chief hacking officer at security management tools firm AlienVault, described the vulnerability as presenting a "high threat" to eBay users before it was fixed.
"If this hadn't been fixed I'd consider this a high threat, specially considering the type of site," Karg explained.
"Implications could range from abusing eBay's trust and tricking [the users] into some download... to potentially playing with the auctions: placing bids on items the user doesn't want / buyouts, accessing his/her account, selling fake stuff and similar."
Cross Site Scripting (XSS) is a type of web server vulnerability that allows attackers to represent code as coming from the site they are visiting while it is actually being served from somewhere else entirely - potentially a hacker-controlled site. It is one of the most common categories of web security vulnerability, but the impact from XSS flaws varies greatly.
“In my experience XSS vulnerabilities always have gotten more attention than they deserve," Karg explained. "First of all, you're attacking other visitors, not the site itself."
He added that there are two types of XSS vulnerability: persistent and reflected. The eBay vulnerability fell into the first, more serious, category, according to Karg, so it's just as well it has been resolved sooner rather than later. ®