Nextcloud Server is a self hosted personal cloud system. Nextcloud Server prior to 29.0.15, 30.0.9, and 31.0.3 and Nextcloud Enterprise Server prior to 26.0.13.15, 27.1.11.15, 28.0.14.6, 29.0.15, 30.0.9, and 31.0.3 have a bug with session handling. The bug caused skipping the second factor confirmation after a successful login with the username and password when the server was configured with remember_login_cookie_lifetime set to 0, once the session expired on the page to select the second factor and the page is reloaded. Nextcloud Server 29.0.15, 30.0.9, and 31.0.3 and Nextcloud Enterprise Server is upgraded to 26.0.13.15, 27.1.11.15, 28.0.14.6, 29.0.15, 30.0.9 and 31.0.3 contain a patch. As a workaround, set the remember_login_cookie_lifetime in config.php to a value other than 0, e.g. 900. Beware that this is only a workaround for new sessions created after the configuration change. System administration can delete affected sessions.
When an actor claims to have a given identity, the product does not prove or insufficiently proves that the claim is correct.