An issue was discovered in Plataformatec Devise before 4.7.1. It confirms accounts upon receiving a request with a blank confirmation_token, if a database record has a blank value in the confirmation_token column. (However, there is no scenario within Devise itself in which such database records would exist.)

Plataformatec Devise version 4.5.0 and earlier, using the lockable module contains a CWE-367 vulnerability in The `Devise::Models::Lockable` class, more specifically at the `#increment_failed_attempts` method. File location: lib/devise/models/lockable.rb that can result in Multiple concurrent requests can prevent an attacker from being blocked on brute force attacks. This attack appear to be exploitable via Network connectivity - brute force attacks. This vulnerability appears to have been fixed in 4.6.0 and later.