Malicious hackers who are able to hijack an organizations Web domain may be able to steal traffic from the legitimate Web site long after the domain has been restored to its owner, according to a recent report.
Design flaws in the way Web browsers and proxy servers store data about Web sites allow malicious hackers to continue directing Web surfers to malicious Web pages for days or even months after the initial domain hijacking.
The persistent attack could lead to information or identity theft, according to Amit Klein, a Web application security researcher with the Web Application Security Consortium.
The problem, which Klein termed "domain contamination" exists because of features in Web proxy servers, which store versions of Web pages, and Web "clients," or browsers, including Microsofts Internet Explorer, the Mozilla Foundations Firefox and the Opera browser.
Proxy servers and browsers both establish trust relationships with Web servers that are identified as the authoritative host for a Web page in the DNS (domain name system), Klein said.
"Once a client believes it is communicating with the legitimate server for some domain, theres an implicit trust thats placed in that server that is not revoked," Klein told eWEEK.
For example, Web browsers store information on the Web server in Web cookies and cached Web pages that are stored locally. Once that information is downloaded and stored on the client, it can be very difficult to get rid of them, Klein said.
"Theres just no way to sterilize the view or reflection of a Web site on the Internet," he said.
Domain hijacking is a recurrent problem on the Internet that occasionally gets mainstream attention, such as when aljazeera.net, the Web domain for Arab satellite television network, was hijacked in March, 2003.
More recently, unknown hackers carried out a massive DNS poisoning attack on DNS servers worldwide in March, 2005.
That attack used a known vulnerability in a Symantec firewall as well as known weaknesses in Windows NT and Windows 2000 machines to change the DNS record for Web sites.
The attack caused unknown numbers of Web surfers to be directed to malicious Web sites that installed spyware and other malicious programs, according to the SANS Institutes Internet Storm Center.
In those attacks, and others, domain hosting companies and Internet infrastructure providers moved quickly to restore control of the Web domain to its proper owner and reset DNS servers that have been compromised, ending the attack.
However, attackers can modify HTTP headers or HTML content on their attack Web site to ensure that it is stored locally for months or even years, Klein said.
Internet users who were caught up in the attack will retain that cached copy of the attackers site in their browser. The cached page may be the first loaded when the victim attempts to visit that Web page.
A sophisticated attacker who embedded scripts in the malicious page could continue to steal information from the victim long after the attack.
For example, a script could harvest information from cookies used by the Web site, or load the actual Web page inside a frame in the cached page to conduct an attack that captures the interactions of the user on the page, Klein wrote.
Also, proxy Web servers that store cached content can, in certain circumstances, revalidate that content, prolonging the life of hijacked Web pages, Klein wrote.
The problem with domain contamination is caused by a major design flaw in the way Web domains are managed, Klein told eWEEK.
"Web browsers dont have any information about domain ownership or any versioning … From the browsers perspective, the google.com now and google.com of five years ago are the same domain with the same privileges," Klein said.
"If they assigned a cookie five years ago, unless it expires naturally, theres no way to verify that the same owner is behind it."
Individuals who have the poisoned domain information can get rid of it simply by deleting affected browser cookies or clearing out their Web page cache—standard features on almost every Web browser.
However, organizations or individuals who have had their Web domain hijacked dont know which of their visitors went to the hijacked site and, thus, have little recourse to rectify the domain poisoning.
"The best response is not to get hijacked to begin with," said Johannes Ullrich, CTO at the SANS ISC. "Once its happened, theres little that you can do about it."
Using SSL (Secure Sockets Layer) to access a Web site can prevent DNS hijacking and Web cache poisoning, and changing your Web server responses to requests from proxy servers can keep them from holding onto poisoned cached content, Klein wrote.