Tell Me About Yourself: The Malicious CAPTCHA Attack

We present the malicious CAPTCHA attack, allowing a rogue website to trick users into unknowingly disclosing their private information. The rogue site displays the private information to the user in obfuscated manner, as if it is a CAPTCHA challenge; the user is unaware that solving the CAPTCHA, results in disclosing private information. This circumvents the Same Origin Policy (SOP), whose goal is to prevent access by rogue sites to private information, by exploiting the fact that many websites allow display of private information (to the user), upon requests from any (even rogue) website. Information so disclosed includes name, phone number, email and physical addresses, search history, preferences, partial credit card numbers, and more. The vulnerability is common and the attack works for many popular sites, including nine out of the ten most popular websites. We evaluated the attack using IRB-approved, ethical user experiments.