Seeking to make money from mistyped website names, some of the United States' largest ISPs instead created a massive security hole that allowed hackers to use web addresses owned by eBay, PayPal, Google and Yahoo, and virtually any other large site.

The vulnerability was a dream scenario for phishers and cyber attackers looking for convincing platforms to distribute fake websites or malicious code.

The hole was quickly and quietly patched Friday after IOActive security researcher Dan Kaminsky reported the issue to Earthlink and its technology partner, a British ad company called Barefruit. Earthlink users, and some Comcast subscribers, were at risk.

Kaminsky warns that the underlying danger lingers on.

"The entire security of the internet is now dependent on some random ad server run by some British company," Kaminsky said.

At issue is a growing trend in which ISPs subvert the Domain Name System, or DNS, which translates website names into numeric addresses.

When users visit a website like Wired.com, the DNS system maps the domain name into an IP address such as 72.246.49.48. But if a particular site does not exist, the DNS server tells the browser that there's no such listing and a simple error message should be displayed.

But starting in August 2006, Earthlink instead intercepts that Non-Existent Domain (NXDOMAIN) response and sends the IP address of ad-partner Barefruit's server as the answer. When the browser visits that page, the user sees a list of suggestions for what site the user might have actually wanted, along with a search box and Yahoo ads.

The rub comes when a user is asking for a nonexistent subdomain of a real website, such as http://webmale.google.com, where the subdomain webmale doesn't exist (unlike, say, mail in mail.google.com). In this case, the Earthlink/Barefruit ads appear in the browser, while the title bar suggests that it's the official Google site.

As a result, all those subdomains are only as secure as Barefruit's servers, which turned out to be not very secure at all. Barefruit neglected basic web programming techniques, making its servers vulnerable to a malicious JavaScript attack. That meant hackers could have crafted special links to unused subdomains of legitimate websites that, when visited, would serve any content the attacker wanted.

The hacker could, for example, send spam e-mails to Earthlink subscribers with a link to a webpage on money.paypal.com. Visiting that link would take the victim to the hacker's site, and it would look as though they were on a real PayPal page.

Kaminsky demonstrated the vulnerability by finding a way to insert a YouTube video from 80s pop star Rick Astley into Facebook and PayPal domains. But a black hat hacker could instead embed a password-stealing Trojan. The attack might also allow hackers to pretend to be a logged-in user, or to send e-mails and add friends to a Facebook account.

Earthlink isn't alone in substituting ad pages for error messages, according to Kaminsky, who has seen similar behavior from other major ISPs including Verizon, Time Warner, Comcast and Qwest. Earlier this month, Network Solutions, one of the net's largest domain name registrars, was caught creating link farms on nonexistent subdomains of websites owned by its own customers.

DNS expert Paul Vixie, who is the president of the nonprofit Internet Systems Consortium, says the problem Kaminisky found isn't with the core internet protocols, which he could fix, but instead is a "problem exacerbated by inappropriate monetization of certain DNS features."

Vixie compared this ISP behavior to Verisign's 2003 Site Finder project, which it unilaterally launched in September 2003 and then shut down a month later.

In that case, VeriSign, which controls the sales of .com and .net top-level domains through a contract with the U.S. government, began directing users who mistyped domains names to its own servers, where it presented paid search results.

The move outraged the technical community and eventually led to an ICANN commission report (.pdf) condemning the practice and an unsuccessful VeriSign lawsuit against ICANN.

"Sitefinder showed that [Non-Existent] domain re-mapping is bad for the community," Vixie said. "This would be an example of why it is bad."

While Barefruit fixed the immediate JavaScript hole, the underlying problem – that large ISPs are ignoring a core internet practice to make money and pretending to be sites that don't exist – means every site on the net remains vulnerable in ways they have no control over, according to Kaminsky.



Kaminsky said he'd talked this week to many internet companies who were pissed, though not at him.

"I can't secure the web as long as ISPs are injecting other content into web pages," he said.

The hole shows the risks of allowing ISPs to violate Net Neutrality principles that seek to keep the internet a series of dumb pipes, according to Kaminsky.

"There's no contractual obligation for ISPs not to change content and inject ads," Kaminsky notes.

For its part, Earthlink says the Barefruit ad pages are useful to users.

"We offer DNS error functionality for our customers through Barefruit to enhance our users' experience, and we work closely with Barefruit to provide a safe and convenient way for them to find the destination they're looking for online," Earthlink spokesman Chris Marshall said via e-mail. "We believe that the service provides a positive experience for our Internet users."

Barefruit echoes the sentiment.

"Barefruit endeavors to ensure online security while providing an improved internet user interface by replacing unhelpful and confusing error messages with alternatives relevant to what the user was seeking," Barefruit's Dave Roberts said via e-mail.

For Vixie, however, the issue is simple.

"I really feel if someone goes to a website that does not exist, they ought to see an error message," Vixie said.

Earthlink customers who do not wish to use the service can instead use different Earthlink DNS servers. Anyone can also use OpenDNS, a start-up that also provides ad pages on domains that don't resolve, but does so without pretending to be the other site.

The news of the massive security breach by compromising net neutrality for profit comes just two days after the Federal

Communication Commission held a hand-wringing public forum at Stanford University over whether it should punish Comcast for its violation of standard internet practices. The broadband provider was caught sending fake packets to its users in order to reduce the bandwidth consumed by peer-to-peer applications.

Kaminsky is demoing the hole publicly on Saturday at the Toorcon security conference in Seattle.

Kaminsky, a well-respected security expert, is perhaps best known for cleverly proving that a spyware rootkit Sony included on music CDs infected computers in more than half a million computer networks in 2005.

Photo: Quinn Norton/Wired.com, Screenshots: Attack application and "Rick-Rolled" Facebook page courtesy of Dan Kaminsky

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