If you think you're safe from man-in-the-middle (MITM) attacks as long as you're visiting an Extended Validation SSL (EV SSL) site, then think again: Researchers will release a new tool at Black Hat USA later this month that lets an attacker hack into a user's session on an EV SSL-secured site.

Mike Zusman and Alex Sotirov -- who in March first demonstrated possible MITM attacks on EV SSL at CanSecWest -- will release for the first time their proxy tool at the Las Vegas conference, as well as demonstrate variations on the attacks they have discovered. The Python-based tool can launch an attack even with the secure green badge displaying on the screen: "It doesn't alert the user that anything fishy is going on," says Zusman, principal consultant at Intrepidus.

All it takes is an attacker having a non-EV SSL certificate for a Website, and he or she can hijack any SSL session that connects to it. That's because the Web browser treats the EV SSL certificate with the same level of trust as an SSL domain-level certificate. "There's no differentiation between the two certs beyond the green badge," Zusman says. If an attacker has a valid domain-level certificate, he can spoof EV SSL connections and execute an MITM attack, with access and view of all sensitive data in the session -- all while the unsuspecting victim still sees that reassuring green badge displayed by his browser.