Nextcloud Deck is a kanban style organization tool aimed at personal planning and project organization for teams integrated with Nextcloud. A user with access to a deck board was able to access comments and attachments of already deleted cards. It is recommended that the Nextcloud Deck app is upgraded to 1.6.6 or 1.7.5 or 1.8.7 or 1.9.6 or 1.11.3 or 1.12.1.
https://hackerone.com/reports/2289333
https://github.com/nextcloud/security-advisories/security/advisories/GHSA-x45g-vx69-r9m8