sean cassidy : Browser Extension Password Managers Should Not Be Used

It's been over a year since I presented LostPass at ShmooCon, and in that time, many more bugs have been found in password managers. The most severe of which are in browser-based password managers extensions, like LastPass.

This should be obvious to everyone who has been paying attention: browser-based password manager extensions should no longer be used as they are fundamentally risky and have the potential to have all of your credentials stolen without your knowledge, by a random malicious website you visit, or by malvertising.

Here's the thing: when you use a browser extension password manager, you're giving attackers an API to interact with your password manager via JavaScript or the DOM. That's how LostPass worked, and it's how many of the new attacks work, too. Desktop-based password managers have no such access, as they require compromising the local machine first, which is much harder than visiting a webpage.

Your password manager de jour might not be as bug ridden as LastPass, but it suffers from the same risk vector if it's a browser extension. If you're using it in a corporate environment to share passwords, now only one user of many needs to be attacked to steal all of your passwords via a previously undisclosed bug. If you think criminals aren't mining LastPass and others for bugs right now, you're naive.


What should you use instead?

Desktop-based Password Managers

Any program which is not resident in your browser is safer than one that isn't. There are many choices to choose from in this category, and none of them suffer from the direct-access-via-JavaScript risk category. If you do use one, do not install the "form filler" browser extensions. Copy and paste the passwords. I use pass because it's simple to understand for technical folks, but I have many friends who use KeePass.

Copying and pasting passwords into the wrong place is not a large enough risk to use an even riskier browser password manager extension. If you accidentally paste one password in the wrong place, it is easy to change. If you get all your passwords stolen by a new bug, you'll never even know, and you'll have little to no recourse.

Built-in Browser Password Managers

Every major browser now has a well designed built-in password manager that is easy to use. These are a nice choice if you dislike copying and pasting passwords into websites. All of them also offer mobile sync so you can have your passwords on the go. Since two factor authentication is not available for these, use a very strong and unique passphrase.

I recommend that non-technical users use the built-in password managers because they're easy to use and plenty secure.

Literally anything else

An encrypted text file on your computer is safer than a browser extension password manager. Think of how it would be compromised: someone would need to get at least user-level access to your computer, and then either read it when it's temporarily unencrypted, or wait for you to unencrypt it. That cannot be done by efficient attackers at scale. And if they've compromised your machine, you have bigger things to worry about.

The future

I don't know if these browser extension password managers will ever improve enough for me to recommend them. The risk of having an attacker be able to directly interact with them is just too high. Many of them are for-profit companies who obviously have not invested a lot of resources in an in-depth audit of their source code because of the trivial bugs that are found by researchers in an hour.

We need less of the "military grade encryption" marketing from them and more "here's the full source code audit report by a well known security firm". Maybe then it'll get better.


  1. Genius Blocker
  2. LostPass
  3. Privilege
  4. Your Own Verifiable Hardware RNG with bladeRF SDR
  5. When names outlive their usefulness
  6. Diagnosis of the OpenSSL Heartbleed Bug
  7. The Story of the GnuTLS Bug
  8. Don't Pipe to your Shell