Nextcloud Server is a self hosted personal cloud system. The OAuth2 client secrets were stored in a recoverable way, so that an attacker that got access to a backup of the database and the Nextcloud config file, would be able to decrypt them. It is recommended that the Nextcloud Server is upgraded to 28.0.10 or 29.0.7 and Nextcloud Enterprise Server is upgraded to 27.1.11.8, 28.0.10 or 29.0.7.