A teenage whitehat hacker said he has found a simple way that attackers can bypass the two-factor authentication system PayPal uses to protect user accounts.

The circumvention requires little more than spoofing a browser cookie set when users link their eBay and PayPal accounts, according to Joshua Rogers, a 17-year-old living in Melbourne, Australia. Once the cookie—which is tied to a function PayPal identifies as "=_integrated-registration"—is active in a user's browsing session, the two-factor authentication is circumvented, Rogers reported. That means attackers who somehow acquire someone else's login credentials would be able to log in without having to enter the one-time passcode sent to the account holder's mobile phone.

Rogers said he reported the vulnerability privately to PayPal on June 5. He said he went public two months later after receiving no response. He went on to write:

Once you're actually logged in, a cookie is set with your details, and you're redirected to a page to confirm the details of the process. And this is where the exploit lays. Now just load http://www.paypal.com/ and you are logged in and don't need to re-enter your login. So, the actual bug itself is that the "=_integrated-registration" function does not check for a 2FA code, despite logging you into PayPal. You could repeat the process using the same "=_integrated-registration" page unlimited times.

The technique does require an attacker to have the victim's password—but that's precisely the scenario two-factor authentication is supposed to protect against.

Rogers is the same hacker who in January was reported to police after finding a vulnerability in a government website. He has provided a video demonstration of the PayPal vulnerability, embedded below.

Update: PayPay officials have released the following statement: