Visual Spoofing of SSL Protected Web Sites and Effective Countermeasures

Today the standard means for secure transactions in the World Wide Web (WWW) are the SSL/TLS protocols, which provide secure (i.e., private and authentic) channels between browsers and servers. As protocols SSL/TLS are considered secure. However, SSL/TLS’s protection ends at the “transport/session layer” and it is up to the application (here web browsers) to preserve the security offered by SSL/TLS. In this paper we provide evidence that most web browsers have severe weaknesses in the browser-to-user communication (graphical user interface), which attackers can exploit to fool users about the presence of a secure SSL/TLS connection and make them disclose secrets to attackers. These attacks, known as “Visual Spoofing”, imitate certain parts of the browser’s user interface, pretending that users communicate securely with the desired service, while actually communicating with the attacker. Therefore, most SSL/TLS protected web applications can not be considered secure, due to deficiencies in browser’s user interfaces. Furthermore, we characterise Visual Spoofing attacks and discuss why they still affect today’s WWW browsers. Finally, we introduce practical remedies, which effectively prevent these attacks and which can easily be included in current browsers or (personal) firewalls to preserve SSL/TLS’s security in web applications.