Nextcloud Server is a self hosted personal cloud system. Due to a pre-flighted HEAD request, the link reference provider could be tricked into downloading bigger websites than intended, to find open-graph data. 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.