Nextcloud Tables allows you to create your own tables with individual columns. Prior to 0.8.6 and 0.9.3, a malicious user was able to create their own table and then move a column to a victims table. This vulnerability is fixed in 0.8.6 and 0.9.3.
https://hackerone.com/reports/3137895
https://github.com/nextcloud/tables/pull/1810
https://github.com/nextcloud/tables/commit/39f24a62fb41fd7a8bda65325f8bbafdc91c731c
https://github.com/nextcloud/security-advisories/security/advisories/GHSA-w787-vwqp-8wr7