This module enables you to require a second authentication factor (a time-based one-time password from an authenticator app) when users log in. Under certain circumstances, an attacker can make the module treat a login as having passed the password check when it did not, or reach the two-factor setup page of another account. Depending on the site's configuration, this can allow the attacker to take over an account that has 2FA enabled without knowing its password or its second factor. This vulnerability is mitigated by the fact that the attacker must have an account of their own on the site, must already control the victim's email address or know the victim's password, and must win a timing-dependent race.