On the Security of Password Managers

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Source: Schneier
On the Security of Password Managers

There’s new research on the security of password managers, speficially 1Password, Dashlane, KeePass, and Lastpass. This work specifically looks at password leakage on the host computer. That is, does the password manager accidentally leave plaintext copies of password lying around memory?

All password managers we examined sufficiently secured user secrets while in a ‘not running’ state. That is, if a password database were to be extracted from disk and if a strong master password was used, then brute forcing of a password manager would be computationally prohibitive.

Each password manager also attempted to scrub secrets from memory. But residual buffers remained that contained secrets, most likely due to memory leaks, lost memory references, or complex GUI frameworks which do not expose internal memory management mechanisms to sanitize secrets.

This was most evident in 1Password7 where secrets, including the master password and its associated secret key, were present in both a locked and unlocked state. This is in contrast to 1Password4, where at most, a single entry is exposed in a ‘running unlocked’ state and the master password exists in memory in an obfuscated form, but is easily recoverable. If 1Password4 scrubbed the master password memory region upon successful unlocking, it would comply with all proposed security guarantees we outlined earlier.

This paper is not meant to criticize specific password manager implementations; however, it is to establish a reasonable minimum baseline which all password managers should comply with. It is evident that attempts are made to scrub and sensitive memory in all password managers. However, each password manager fails in implementing proper secrets sanitization for various reasons.

For example:

LastPass obfuscates the master password while users are typing in the entry, and when the password manager enters an unlocked state, database entries are only decrypted into memory when there is user interaction. However, ISE reported that these entries persist in memory after the software enters a locked state. It was also possible for the researchers to extract the master password and interacted-with password entries due to a memory leak.

KeePass scrubs the master password from memory and is not recoverable. However, errors in workflows permitted the researchers from extracting credential entries which have been interacted with. In the case of Windows APIs, sometimes, various memory buffers which contain decrypted entries may not be scrubbed correctly.

Whether this is a big deal or not depends on whether you consider your computer to be trusted.

Several people have emailed me to ask why my own PasswordSafe was not included in the evaluation, and whether it has the same vulnerabilities. My guess about the former is that PasswordSafe isn’t as popular as the others. (This is for two reasons: 1) I don’t publicize it very much, and 2) it doesn’t have an easy way to synchronize passwords across devices or otherwise store password data in the cloud.) As to the latter: we tried to code PasswordSafe not to leave plaintext passwords lying around in memory.

So, Independent Security Evaluators: take a look at PasswordSafe.

Also, remember the vulnerabilities found in many cloud-based password managers back in 2014?

News article. Slashdot thread.

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