New SSL attack can steal sensitive info from secure Web sites

Security researcher has developed generic attack code that could give hackers a very powerful phishing tool, but is keeping it private

A Seattle computer security consultant says he's developed a new way to exploit a recently disclosed bug in the SSL protocol, used to secure communications on the Internet. The attack, while difficult to execute, could give attackers a very powerful phishing attack.

Frank Heidt, CEO of Leviathan Security Group, says his "generic" proof-of-concept code could be used to attack a variety of Web sites. While the attack is extremely difficult to pull off -- the hacker would first have to first pull off a man-in-the-middle attack, running code that compromises the victim's network -- it could have devastating consequences.

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The attack exploits the SSL (Secure Sockets Layer) Authentication Gap bug, first disclosed on Nov. 5. One of the SSL bug's discoverers, Marsh Ray at PhoneFactor, says he's seen a demonstration of Heidt's attack, and he's convinced it could work. "He did show it to me and it's the real deal," Ray said.

The SSL Authentication flaw gives the attacker a way to change data being sent to the SSL server, but there's still no way to read the information coming back. Heidt sends data that causes the SSL server to return a redirect message that then sends the Web browser to another page. He then uses that redirect message to move the victim to an insecure connection where the Web pages can be rewritten by Heidt's computer before they are sent to the victim.

"Frank has shown a way to leverage this blind plain text injection attack into a complete compromise of the connection between the browser and the secure site," Ray said.

A consortium of Internet companies has been working to fix the flaw since the PhoneFactor developers first uncovered it several months ago. Their work gained new urgency when the bug was inadvertently disclosed on a discussion list. Security experts have been debating the severity of this latest SSL flaw since it became public knowledge.

Last week, IBM researcher Anil Kurmus showed how the flaw could be used to trick browsers into sending Twitter messages that contained user passwords.

This latest attack shows that the flaw could be used to steal all sorts of sensitive information from secure Web sites, Heidt said.

To be vulnerable, sites need to do something called client renegotiation under SSL and also to have some element on their secure Web pages that could generate a particular 302 redirect message.

Many high-profile banking and e-commerce Web sites will not return this 302 redirect message in a way that can be exploited, but a "huge number" of sites could be attacked, Heidt said.

With so many Web sites at risk to the flaw, Heidt says he does not intend to release his code immediately.

From the victim's perspective, the only noticeable change during an attack is that the browser no longer looks as though it's connected to an SSL site. The attack is similar to the SSL Strip attack demonstrated by Moxie Marlinspike [cq] at a security conference earlier this year.

Leviathan Security Group has created a tool that Webmasters can use to see if their sites are vulnerable to a SSL Authentication Gap attack.

Because SSL, and its replacement standard, TLS, are used in a wide range of Internet technologies the bug has far-reaching implications.

Thierry Zoller, a security consultant with G-Sec, says that theoretically, the flaw could be used to attack mail servers. "An attacker can potentially highjack mails send over secured SMTP [Simple Mail Transfer Protocol] connections, even if they are authenticated by a private certificate," he said in an instant message interview.

Zoller, who has not seen Leviathan's code, said that if the attack works as advertized, it will be just a matter of days before someone else figures out how to do it.