If you use the autocomplete features in Safari, certain versions of IE, Firefox, or Chrome, you could be making yourself vulnerable to identity theft and other attacks, according to one security researcher scheduled to speak at the Black Hat conference next week. WhiteHat Security CTO Jeremiah Grossman says that the four major browsers have critical weaknesses that have yet to be addressed by their respective companies, and could expose users' passwords, e-mail addresses, and more to attackers.

Grossman plans to demo a proof-of-concept attack at next week's conference. As most of us know, if you have autocomplete turned on in many browsers, you just have to begin typing a letter or two in one of the fields before they all fill in with your name and address, possibly your credit card number, and more. Grossman says attackers can simply create a page with hidden form fields that use JavaScript to enter letters and numbers into each field until it finds one that's a hit, and the browser autocompletes it.

Users don't even have to enter a single letter for the attack to work—all they have to do is load the page, and they likely wouldn't even be aware of what's happening.

According to Grossman, the autocomplete exploit works in the two most recent versions of Safari (4 and 5), as well as IE 6 and 7. Firefox and Chrome aren't susceptible to this particular attack, though they were vulnerable to another one: Grossman says that the two browsers can expose stored usernames and passwords for saved sites, making it possible for a cross-site scripting vulnerability to grab the info when a user logs into a Google account or Facebook, for example.

The reason he plans to expose these vulnerabilities at Black Hat is because the companies in question have apparently not responded to Grossman's attempts to contact them about it. "I would never have talked about this publicly if Apple had taken this seriously," Grossman told The Register. "I figured somebody else must have found this before because it's so brain-dead simple.” When he sent a follow-up query “I never heard anything back, human or robotic."