Intellectual Property Law

Vulnerabilities Allow Attacker to Impersonate Any Website

By Kim Zetter

LAS VEGAS — Two researchers examining the processes for issuing web certificates have uncovered vulnerabilities that would allow an attacker to masquerade as any website and trick the user into providing him with sensitive communications.

Normally when a user visits a secure website, such as Bank of America, Paypal or Ebay, the browser examines the website’s certificate to verify its authenticity.

However, IOActive researcher Dan Kaminsky and independent researcher Moxie Marlinspike, working separately, presented nearly identical findings at the Black Hat security conference Wednesday that demonstrated how an attacker can legitimately obtain a certificate with a special character in the domain name that would fool nearly all popular browsers into believing an attacker is whichever site he wants to be.

The problem occurs in the way that browsers implement Secure Socket Layer communications.

Certificates for authenticating SSL communications are obtained through Certificate Authorities (CAs) such as VeriSign and Thawte and are used to initiate a secure channel of communication between the user’s browser and a website. When an attacker who owns his own domain — badguy.com — requests a certificate from the CA, the CA, using contact information from Whois records, sends him an email asking to confirm his ownership of the site. But an attacker can also request a certificate for a subdomain of his site, such as Paypal.com\0.badguy.com, using the null character \0 in the URL.

The CA will issue the certificate for a domain like PayPal.com\0.badguy.com because the hacker legitimately owns the root domain badguy.com.

Then, due to a flaw found in the way SSL is implemented in many browsers, Firefox and others theoretically can be fooled into reading his certificate as if it were one that came from the authentic PayPal site. Basically when these vulnerable browsers check the domain name contained in the attacker’s certificate, they stop reading any characters that follow the “/0″ in the name.

More significantly, an attacker can also register a wildcard domain, such as *\0.badguy.com, which would then give him a certificate that would allow him to masquerade as any site on the internet and intercept communication.

Marlinspike said he will be releasing a tool soon that automates this interception.

It’s an upgrade to a tool he released a few years ago called SSLSniff, which sniffs traffic going to secure web sites that have an https URL in order to conduct a man-in-the-middle attack. The user’s browser examines the attacker’s certificate sent by SSLSniff, believes the attacker is the legitimate site and begins sending data, such as log-in information, credit card and banking details or any other data through the attacker to the legitimate site. The attacker sees the data unencrypted.

A similar man-in-the-middle attack would allow someone to hi-jack software updates for Firefox or any other application that uses Mozilla’s update library. When the user’s computer initiates a search for a Firefox upgrade, SSLSniff intercepts the search and can send back malicious code that is automatically launched on the user’s computer.

Marlinspike said Firefox 3.5 is not vulnerable to this and that Mozilla is working on patches for 3.0.

(Dave Bullock contributed to this article.)

Photo of Moxie Marlinspike by Dave Bullock.

Full post as published by Threat Level on July 29, 2009 (boomark / email).