Pierluigi Paganini August 06, 2014

A Security researcher has discovered a new flaw in the two-factor authentication process implemented by PayPal to protect its users.

Security researcher Joshua Rogers has discovered a simple way of bypassing the two-factor authentication mechanism implemented by PayPal to protect accounts that are linked to eBay accounts.

The flaw resides in the login process when a user is prompted to connect his eBay account to his PayPal account.

Every eBay user knows that is very easy to pay the items using his PayPal account linked to his eBay account. A user can decide not to tie the accounts together, but if he continues through the dialogue to connect them, he is presented with a page that asks for his PayPal login information.

“When you are redirected to the login page(above), the URL contains ‘=_integrated-registration’. Doing a quick Google search for this shows that it isn’t used for anything other than eBay; thus it is setup purely for Paypal&eBay,” “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.” explained Rogers in a blog post.

PayPay service implements a two-factor authentication mechanism to protect users’ accounts, the flaw discovered by the researcher is related to the integrated registration function that doesn’t check for the one time 2FA code which user should have to provide to complete the login process, this means that the 2FA is by passed.

PayPal two-factor authentication is based on one-time codes sent via SMS to the user’s mobile either generated by a dedicated device, once enabled 2FA users must provide the above password to access their account meanwhile exploiting the above flaw it is possible to bypass this mechanism.  Now imagine that an attacker has syphoned username and password by a PayPal user with two-factor authentication enabled,  the bad actor could access the account and send money exploiting the flaw discovered by Roger.

Rogers ethically reported the bug to PayPal in June and the company said it planned to fix it, but in time he is writing the flaw is still exploitable. Rogers provided details of the flaw and a proof of concept video in his post.

The isn’t first time security experts discover a vulnerability in the two-factor authentication process designed by PayPal, recently experts at Duo Security firm disclosed a serious flaw in the implementation of 2FA which allow attackers to bypass it.

Pierluigi Paganini

(Security Affairs –  PayPal, two-factor authentication)