LastPass is in part able to achieve the highest level of security for our users by looking to our community to challenge our technology.
In August 2013, a security researcher at UC Berkeley, Zhiwei Li, contacted us to responsibly disclose novel vulnerabilities with the LastPass bookmarklets (actively used by less than 1% of the user base) and One Time Passwords (OTPs). Zhiwei discovered one issue that could be exploited if a LastPass user utilized the bookmarklet on an attacking site, and another issue if the LastPass user went to an attacking site while logged into LastPass, and used their username to potentially create a bogus OTP.
Zhiwei only tested these exploits on dummy accounts at LastPass and we don't have any evidence they were exploited by anyone beyond himself and his research team. The reported issues were addressed immediately, as confirmed by their team, and we let them publish their research before discussing it.
If you are concerned that you’ve used bookmarklets before September 2013 on non-trustworthy sites, you may consider changing your master password and generating new passwords, though we don’t think it is necessary.
Regarding the OTP attack, it is a “targeted attack”, requiring an attacker to know the user’s username to potentially exploit it, and serve that custom attack per user, activity which we have not seen. Even if this was exploited, the attacker would still not have the key to decrypt user data. If you’d like to check your current OTPs you can do so here: https://lastpass.com/otp.php
We appreciate that, as the most popular password manager in the world, we have an active, dedicated community that challenges us to be better and is committed to helping us improve the security of our service. Again, we thank Zhiwei and his team for their important research.
Joe & The LastPass Team