LastPassSteve Thomas, aka Sc00bz, has brought up some very interesting issues about the LastPass password monitor that are causing some confusion so I thought I’d give another perspective on the issue.

Summary of Steve’s points:

  1. When you use the LastPass web site to login to your account, your web browser will first send a hash with a single iteration, no matter how many iterations you have set for your account. It isn’t until this hash fails that the browser tells the user the correct number of iterations to use.
  2. LastPass has a default setting of 500 iterations (at least at that time, now it recommends 5000 iterations).
  3. The extension should warn you if it is going to send a hash with fewer iterations than what you have set.
  4. LastPass does not encrypt the URLs of sites stored in your password database

LastPass hashes your password rather than sending the plain text to the server when you login. The algorithm it uses is sha256(sha256(email + password) + password). This hash, while not necessarily insecure, can be cracked in a reasonable amount of time with ordinary hardware, unless the user has a relatively strong password. It isn’t until after this single iteration hash is sent that the LastPass server responds and tells the browser exactly how many iterations it should use; hash is sent again using the correct number of iterations. More iterations means it will take much more time to crack your password. A good minimum number of iterations is 5,000. If you go too high with the number of iterations, some clients such as mobile phones may be very slow logging in.

This is an issue that certainly should be addressed, but it is not serious enough to warrant abandoning LastPass

The mitigating factors here are:

  1. You are logging in via SSL so the primary threats here are a MitM attack with spoofed SSL certificates, a government warrant, or a government spy agency.
  2. They still need to crack your hash so if you have a very strong password, even a single iteration hash could provide a reasonable amount of protection.
  3. A second factor of authentication, country restrictions, blocking tor logins,  restricting mobile access, and other settings still protect your account from unauthorized logins, unless the attacker is able to obtain your stored hashes through hacking, warrant, or spying.

One thing I might also add is that the server is telling the client how many iterations it expects, so this does make an attack much easier if someone acquires your hash.

My opinion is that this is an issue that certainly should be addressed, but it is not serious enough to warrant abandoning LastPass altogether unless your inpidual threat model includes the NSA or other government agencies. The LastPass plugin should identify when someone is logging in to LastPass via the web login and provide the client-side script with the correct number of iterations. The server should never respond with this at all. However, if someone is logging in through a web browser that doesn’t have LastPass with their account data installed, the server sending the number of iterations is the only option.

The only proper solution here is to have your primary login different than the decryption login, at least for accessing the web interface if not everywhere. That way, the number of iterations is never publicly revealed and sending a single iteration hash would be unnecessary. Other companies such as RoboForm use this method. I have always wanted this feature and I would highly recommend LastPass implement this if it is feasible.

As for the other points, the default iteration count mentioned in number 2 has been addressed and the warning mentioned in number 3 would be a good thing to add if it already hasn’t but this would not be possible if using a web browser with your LastPass account installation.


As for encrypting URLs mentioned in number 4, LastPass’s response was that this is necessary to grab favicons. Although unencrypted URLs may not be an issue, there certainly are scenarios where you would want these encrypted. LastPass should make this an option for the user.

LastPass does provide strong security controls, although there clearly is room for improvement. If you do not find LastPass to be secure enough, the only reasonable alternative I would recommend is KeePass, which puts you in complete control over your data while still being quite usable. I would not recommend ditching LastPass, but I would recommend that LastPass address these issues. I would also recommend that Steve Thomas keep up the great research he provides to the community.

I have not heard a recent response from LastPass on these issues but would love to hear from them. I will update this post if and when I do.

Disclosure: I am a LastPass user and I get a free month of premium service whenever someone clicks on banners located on this site. I have no affiliation with LastPass and receive no other compensation from the company. 

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