DNS security guru Dan Kaminsky says the practice by major ISPs to deploy advertising servers within trademarked domains (on error pages, for example) can expose the entire Web to malicious hacker attacks.

Kaminsky (left), a well-known researcher who helped with the Sony rootkit investigation, says the advertising servers are impersonating, via DNS, hostnames within trademarked domains. "We have determined that these injected servers are, in fact, vulnerable to cross-site scripting attacks. Since these servers are being injected into your trademarked domains, their vulnerability can be used to attack your users and your sites," Kaminsky said, identifying EarthLink, Verizon and Quest among the ISPs.

* Photo credit: Dave Bullock (Creative Commons 2.0)

Kaminsky demonstrated the flaw and discussed the security ramifications at the Toorcon Seattle conference this weekend.

During his talk, Kaminsky showed (.ppt file) how the vulnerable ad servers could be exploited for:

1. Arbitrary cookie retrieval. Any Web page on the Internet can retrieve all non-HTTP-only cookies from domains.

2. Fake site injection. A victim can be directed to "server2.www.realsite.com" or "server3.www.realsite.com," which will appear to be a host in a trademarked domain. We believe any phishing attempts from this perfect-address spoofed subdomain are more likely to be successful.

3. Full-page compromise. A victim can be directed to an actual HTTP site, with all logged-in credentials, and a hacker's attack page will still be able to fully manipulate the target site as if we ourselves were the victim. Note, while we cannot attack HTTPS resources, we can prevent upgrade from HTTP to HTTPS. This may affect any shopping carts within your sites.

In a statement sent to eWEEK's SecurityWatch ahead of his talk, Kaminsky said:

We believe this behavior is illustrative of the risks of violating Network Neutrality. Indeed, it is our sense that the HTTP web becomes insecurable if man-in-the-middle attacks are monetized by providers -- if we don't know what bits are going to reach the client, how can we control for flaws in those bits?

Kaminsky, who worked for penetration testing and consulting firm IOActive, said he was able to use a vulnerability in the search injection framework of Earthlink to partially compromise Microsoft's Live.com, eBay, the Associated Press, MySpace, Facebook and every other resource on the Web.

"Whereas Comcast outsources the operation of at least parts of their Washington network to EarthLink (who themselves are using equipment from a company called BareFruit), this is potentially affecting millions of users," he added.

Threat Level's Ryan Singel reported that the BareFruit vulnerability was quietly patched on April 18, 2008, a day before Kaminsky's talk. More from Brian Krebs at SecurityFix.