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.
Nextcloud server is a self hosted personal cloud system. In affected versions OAuth codes did not expire. When an attacker would get access to an authorization code they could authenticate at any time using the code. As of version 28.0.0 OAuth codes are invalidated after 10 minutes and will no longer be authenticated. To exploit this vulnerability an attacker would need to intercept an OAuth code from a user session. It is recommended that the Nextcloud Server is upgraded to 28.0.0. There are no known workarounds for this vulnerability.