What security benefit does 2FA provide a password manager?

Question

It's no secret that many popular password managers (1Password, Dashlane, LastPass, KeePass, and many others) support some form of two-factor authentication. This is often implemented via TOTP or other systems, but it could very well also be U2F-based or similar.

However, TOTP-based two-factor algorithms don't store a secret in their digits, neither does U2F provide the ability to encode a secret in its response.

Given this, this leads me to one of the following assumptions:

• The password manager server will refuse to send you your (encrypted) vault unless you present 2FA credentials,
• Or your password vault has multiple keys, one of which is stored (I'd assume visible to a theoretical rogue employee) on the server and sent down after a 2FA challenge is passed.

Assuming the above is correct, the "second factor" would only be protecting something static: either a static encryption key sent by the server, or the encrypted vault itself. In theory, a rogue employee of a cloud-based password manager would then be able to use their access to either get my vault or one part of my vault's encryption key.

Similarly, non-cloud password managers (such as KeePass) would have the same issue. The 2FA section would only be a measure implemented in code (and, assuming an attacker has enough access, something they'd be able to patch out).

So, unless I've missed something critical here, what real security benefit does 2FA provide on a password vault? How would 2FA realistically protect me against a stolen vault file more than just a strong password?

Answer 1

Online password managers go through a huge amount of effort to not know your master password. It will never be sent to the service. Online password managers that have a web login will have JavaScript that performs cryptographic operations on your master password before sending the hashed master password to the server. This means that there is no chance for an employee to steal your master password as it is never put on the wire.

At least for the network based password managers, the 2FA protects against a network attack, preventing an attacker getting access to your encrypted vault. Just knowing your master password (which may or may not be the encryption key, depending on the password manager) will be insufficient to motivate the server to transmit the vault. This corresponds to:

• The password manager server will refuse to send you your (encrypted) vault unless you present 2FA credentials,

from your question.

Regarding,

• Or your password vault has multiple keys, one of which is stored (I'd assume visible to a theoretical rogue employee) on the server and sent down after a 2FA challenge is passed.

That is not done.

Answer 2

2FA will protect you against 2 attacks: keyloggers and shoulder-surfing.

If someone watches you typing your master password, or a keylogger captures it, the window of opportunity for dumping all your passwords is small. For shoulder surfing, the attacker would need to memorize your password, the 2FA code, login on another computer, and input your credentials before the code expires.

If your cloud password storage does not allow two logins to use the same 2FA code, an attacker will not be able to login even if they capture both your password AND 2FA code and manages to login before the code expires.

You are not protecting the password against the cloud provider, they have a reputation to care about, and their reputation is way more valuable to them than any password you may have. You are protecting it against attacker close to you.

Answer 3

assuming we're talking about a true cloud-based platform, you can't protect from the sum combination of the access employees have as a group - at some level you need to place your trust in the sum of them since across employees they would have enough permission to MitM your sessions anyway & steal secrets at a later point (even if the master password/encryption keys are kept on your side now - at a later point the code your run from them that you expose those keys to could have updates to also be stealing the keys - you trust your keys to that code.. and they control it... the only guarantee you have that the code won't do that in future is their promise, and ideally them going to effort to compartmentalise what it takes for them to be compromised like that so it needs to be more than one employee).

The hope is that they compartmentalise trust in a way where it takes multiple bad actors for something bad to happen.

on the benefit of MFA: What MFA is protecting against though is a whole bunch of threats primarily to your endpoint, including things like shoulder-surfing. Typically these are frankly the bigger threat than a multiple-rogue-employees-targetting-you scenario.

I got downvoted on something where I think my answer ads significant content over what's above: Even if secrets are encrypted in a way where the decryption is done locally on your machine, if you rely on code coming from the cloud-based password-safe provider, they can steal your passwords.

If they were to go rogue they could supply altered code for how the decryption works, in a way where even with decryption using a key you only have on your computer, used to only decrypt the secrets once sent to your device from encrypted cloud-storage, the rogue code in the web-page/plugin that's used as the algorithm for decryption could include javascript/other code to send the secrets back to malicious infrastructure - the security model is only as safe as the total sum of failures it takes (if properly compartmentalised, multiple rogue employees) for your secrets to be stolen in this manner.