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Another Hole Discovered In Secure Sockets Layer (SSL)

Website encryption has sustained another body blow, this time by an independent hacker who demonstrated a tool that can steal sensitive information by tricking users into believing they’re visiting protected sites when in fact they’re not.

Unveiled Wednesday at the Black Hat security conference in Washington, SSLstrip works on public Wi-Fi networks, onion-routing systems, and anywhere else a man-in-the-middle attack is practical. It converts pages that normally would be protected by the secure sockets layer protocol into their unencrypted versions. It does this while continuing to fool both the website and the user into believing the security measure is still in place.

The presentation by a conference attendee who goes by the name Moxie Marlinspike is the latest demonstration of weaknesses in SSL, the encryption routine websites use to prevent passwords, credit card numbers, and other sensitive information from being sniffed while in transit. Similar to side jacking attack from 2007 and last year’s forging of a certificate authority certificate, it shows the measure goes only so far.

Marlinspike said SSLstrip is able to work because the vast majority of sites that use SSL begin by showing visitors an unencrypted page and only offer the protection for sections where sensitive information is transmitted. When a user clicks on a login page, for instance, the tool alters the site’s unencrypted response so the “https” is changed to “http.” The website, however, continues to operate under the assumption the connection is encrypted.

SSLstrip manages to fool the user into believing he has an encrypted connection with the intended website through several clever slights on hand. First, the tool uses a proxy on the local area network that contains a valid SSL certificate, causing the browser to display an “https” in the address bar.

Second, it uses homographic techniques to create a long URL that includes a series of fake slash marks in the address. (To prevent browsers from converting the characters to punycode, he had to obtain a domain-validated SSL wildcard cert for *.ijjk.cn).

Marlinspike has successfully used the ruse on people using both the Firefox and Safari browsers. While he hasn’t tested it on Internet Explorer, he assumes the technique works there too. And even if it doesn’t, he says there’s plenty of reason to believe even security-cautious users don’t take the time to ensure their sessions are encrypted.

To prove his point, he ran SSLstrip on a server hosting a Tor anonymous browsing network. During a 24-hour period, he harvested 254 passwords from users visiting sites including Yahoo, Gmail, Ticketmaster, PayPal, and LinkedIn. The users were fooled even though SSLstrip wasn’t using the proxy feature that tricks them into believing they were at a secure site. Sadly, the Tor users entered passwords even though the addresses in their address bars didn’t display the crucial “https.” (Marlinspike said he later disposed of all personally identifiable information).

The attack is sure to touch off more head-scratching at places like Mozilla, Microsoft and VeriSign, where engineers have been wrestling with ways to make the SSL process more reliable. The easiest countermeasure is for users to type the entire https address into a browser (or better yet store it in a bookmark) so a tool like SSLstrip never gets a chance to alter a website’s unencrypted link.

Credit: The Register

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