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Lastpass and Google Authenticator

Design flaws in Lastpass 2FA implementation

As part of a Red Team engagement I found myself looking for a way to bypass two-factor authentication (2FA) in Lastpass. Unfortunately this happened before Tavis Ormandy reported multiple 0-days in Lastpass. Would have saved us so much time! Anyway, 2FA is an additional layer of security to protect user accounts from attackers that have already compromised your password. I mention this because it is key to understand the purpose of this post.

When you login into a service using your username and password, you will get an additional challenge before access is granted. Usually it is a 6 digit temporary code that changes every 30 seconds. Google authenticator, Authy and Toopher are just a few of the 2FA solutions Lastpass supports that are based on RFC6238 and RFC4226. There are other types of 2FA but these are the most common.

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Venmo post logo

How to steal $2,999.99 in less than 2 minutes with Venmo and Siri

Venmo is a very popular mobile app which simplifies payments among friends. Once you link your bank account or credit card, you can start sending money to others, instantly.

With Venmo, you are not limited to just make payments. It allows you to charge others as well. Say your friend had no cash for that tasty burrito and you paid for it. You have the option to be proactive and “charge” your friend using Venmo. Charging someone does not mean that the money will be withdraw from his account, it just means that he will get a notification and see the pending payment in his account. Your friend has to accept the charge in order for the payment to happen. And this functionality is what we are going to take advantage of.

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