SSLStrip Hacking Tool Released

In an interesting twist, a hacker guessed another hacker's Web page URL and got access to a hacking tool prior to its release. The so-called SSLStrip tool, which basically makes users think they are visiting a secure Website when they are not, was demonstrated at Black Hat DC last week.

Moxie Marlinspike, the hacker who created and demonstrated the tool in his Black Hat session, had been preparing the Web page for releasing the tool when an unknown hacker apparently figured out the URL Marlinspike was using for it and broadcast the URL on Slashdot.

"Greetings slashdotters. Apparently the demand for this has been so great that someone went to the trouble of wardialing for the unpublished URL where sslstrip was being staged on my webserver. Then having guessed the correct URL, and not content to merely have access, they also slashdotted it," Marlinspike wrote in a message on his Website.

Marlispike says he was in the process of getting the page ready to go live, so when the URL hit Slashdot, it wasn't complete. He made the tool officially available for download soon thereafter.

Marlinspike's tool lets an attacker or researcher stage a man-in-the middle attack against a Secure Sockets Layer (SSL) Web session. Marlinspike says there's no simple fix for defending against the attack because it's not a typical software bug or protocol vulnerability that can be patched. "It's hard to fix," he said in an interview. "This attack comes closer to an implementation bug...it's a problem with the way SSL is deployed."

Researchers increasingly have been poking holes in SSL. Most recently, researchers demonstrated at the 25th Chaos Communication Congress in Berlin a hack that exploited a known weakness in the algorithm used in some SSL digital certificates that allows an attacker to impersonate secure Websites.

Security experts haven't been shy about pointing out SSL's shortcomings, either. "There's a reason I described, at length, the limitations of SSL in protecting against DNS cache poisoning. There's also a reason why Extended Validation certificates exist," says Dan Kaminsky, director of penetration testing for IOActive. "SSL has long been vulnerable to users simply not knowing to demand it, or not being able to recognize that www.their-bank.com or www.their.bank.xyz.com isn't their bank."

SSL Extended Validation (EV) is one solution to defending against these SSL attacks. "It's a technology that addresses semantic collisions, like [what] Moxie's demonstrating, with an enhanced user experience," Kaminsky notes.

SSLStrip basically hijacks HTTP traffic, looking out for HTTPS links. It then maps HTTPS links to phony HTTP or HTTPS links. (There's even a phony lock icon it can use to post on the not-really-secure Website). Marlinspike, meanwhile, says the thesis behind the SSL problem is this: "We've been moving away from positive feedback to negative feedback [in Web browsing]," he says. "But that's gotten users [mistakenly] thinking that as long as they browse along and don't get disastrous warnings, all was OK."

Attacks such as Marlinspike's SSL-stripping demonstrate how silent and deadly Web attacks can be for unsuspecting users, experts say.

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