ownCloud 10.7 has an incorrect access control vulnerability, leading to remote information disclosure. Due to a bug in the related API endpoint, the attacker can enumerate all users in a single request by entering three whitespaces. Secondary, the retrieval of all users on a large instance could cause higher than average load on the instance.
https://owncloud.com/security-advisories/cve-2021-29659/
https://doc.owncloud.com/server/admin_manual/release_notes.html