Devise-Two-Factor vulnerable to brute force attacks
Advisory withdrawn
The backing CVE has been rejected
Devise-Two-Factor does not throttle or otherwise restrict login attempts at the server by default. When combined with the Time-based One Time Password algorithm's (TOTP) inherent entropy limitations, it's possible for an attacker to bypass the 2FA mechanism through brute-force attacks.
Impact
If a user's username and password have already been compromised an attacker would be able to try possible TOTP codes and see if they can hit a lucky collision to log in as that user. The user under attack would not necessarily know that their account has been compromised.
Patches
Devise-Two-Factor has not released any fixes for this vulnerability. This library is open-ended by design and cannot solve this for all applications natively. It's recommended that any application leveraging Devise-Two-Factor implement controls at the application level to mitigate this threat. A non-exhaustive list of possible mitigations can be found below.
Mitigations
1. Use the lockable strategy from Devise to lock a user after a certain number of failed login attempts. See https://www.rubydoc.info/github/heartcombo/devise/main/Devise/Models/Lockable for more information.
2. Configure a rate limit for your application, especially on the endpoints used to log in. One such library to accomplish this is [rack-attack](https://rubygems.org/gems/rack-attack).
3. When displaying authentication errors hide whether validating a username/password combination failed or a two-factor code failed behind a more generic error message.
Acknowledgements
Christian Reitter ([Radically Open Security](https://www.radicallyopensecurity.com/)) and Chris MacNaughton ([Centauri Solutions](https://centauri.solutions))
