user_oidc app is an OpenID Connect user backend for Nextcloud. Missing access control on the ID4me endpoint allows an attacker to register an account eventually getting access to data that is available to all registered users. It is recommended that the OpenID Connect user backend is upgraded to 3.0.0 (Nextcloud 20-23), 4.0.0 (Nexcloud 24) or 5.0.0 (Nextcloud 25-28).