OpenProject is open-source, web-based project management software. Prior to 17.3.3 and 17.4.1, there is an IDOR through /projects/<A>/settings/project_storages/<A_ps_id> via PATCH parameter "storages_project_storage[project_folder_id]" leads to Access to Unauthorized Resources. A project-admin in one project can hijack the managed Nextcloud or OneDrive folder of another project on the same storage by writing the victim project's project_folder_id into the attacker's Storages::ProjectStorage row. The next managed-folder sync overwrites the ACL on the referenced folder with the attacker project's user list. This vulnerability is fixed in 17.3.3 and 17.4.1.