Ory Kratos's setting required_aal `highest_available` does not properly respect code + mfa credentials

Preconditions

• The code login method is enabled with the passwordless_enabled flag set to true .
• A 2FA method such as totp is enabled.
• required_aal of the whomai check or the settings flow is set to highest_available. AAL stands for Authenticator Assurance Levels and can range from 0 (no factor) to 2 (two factors).
• A user uses the code method as the only login method available. They do not have a password or any other first factor credential enabled.
• The user has 2FA enabled.
• The user’s available_aal is incorrectly stored in the database as aal1 or aal0 or NULL.
• A user signs in using the code method, but does not complete the 2FA challenge.

Example server configuration

Below you will find an vulnerable example configuration. Keep in mind that, for the account to be vulnerable, the account must have no first factor except the code method enabled plus a second factor.

selfservice:
  methods:
    code:
      # The `code` login method is enabled with the `passwordless_enabled` flag set to `true`
      passwordless_enabled: true
    totp:
      # 2FA method such as `totp` is enabled
      enabled: true
  flows:
    settings:
      # This is set
      required_aal: highest_available
session:
  whoami:
    # Or this
    required_aal: highest_available

Impact

Given the preconditions, the highest_available setting will incorrectly assume that the identity’s highest available AAL is even though it really is . This means that the configuration will act as if the user has only one factor set up, for that particular user. This means that they can call the settings and whoami endpoint without a session, even though that should be disallowed.