http://www.computerworld.com/action/article.do?command=viewArticleBasic&articleId=9001247
By Peter Sayer
IDG News Service
June 16, 2006
A cross-site scripting flaw in the PayPal Web site allows a new
phishing attack to masquerade as a genuine PayPal log-in page with a
valid security certificate, according to security researchers.
Fraudsters are exploiting the flaw to harvest personal details,
including PayPal log-ins, Social Security numbers and credit card
details, according to staff at Netcraft Ltd., an Internet services
company in Bath, England. The PayPal site, owned by eBay Inc., allows
users to make online payments to one another, charged to their credit
cards, and log-in credentials for the service are a prized target of
fraudsters.
The attack works by tricking PayPal members into following a
maliciously crafted link to a secure page on PayPal's site. Anyone
thinking to check the site's security certificate at this point will
see that it is a valid 256-bit certificate belonging to the site,
Netcraft employee Paul Mutton wrote in the company's blog on Friday.
However, the URL (uniform resource locator) exploits a flaw in
PayPal's site that allows the fraudsters to inject some of their own
code into the page that is returned, he wrote. In this case, the
result is a warning that the user's account may have been compromised,
and that they "will now be redirected to Resolution Center." The page
to which they are redirected asks for their PayPal account details --
but thanks to the cross-site scripting flaw in the PayPal site, and
the data injected into the URL by the fraudsters, the page is no
longer on the PayPal site. Instead, the page steals the log-in details
and sends them to the fraudsters' server, then prompts the user for
other personal information, Mutton said.
The Web server harvesting the personal details is hosted in Korea,
Mutton said.
The cross-site scripting technique makes the phishing attempt
difficult to detect, said Mike Prettejohn, also of Netcraft.
If the malicious link arrived by e-mail, then "there would be clues in
the mail that it's not genuine," he said. "It's a technique chosen by
fraudsters because it is hard to spot."
Although there could be benign uses of cross-site scripting to
transfer data between sites, the technique has an inherent security
risk, Prettejohn said. "I don't think people would intentionally use
it," he said.
"If somebody knows there's a cross-site scripting opportunity on their
site, the right thing to do would be to fix it," he said.
Staff at PayPal could not immediately be reached for comment.
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