Deck is an open source kanban style organization tool aimed at personal planning and project organization for teams integrated with Nextcloud. In affected versions the Deck application didn't properly check membership of users in a Circle. This allowed other users in the instance to gain access to boards that have been shared with a Circle, even if the user was not a member of the circle. It is recommended that Nextcloud Deck is upgraded to 1.5.1, 1.4.4 or 1.2.9. If you are unable to update it is advised to disable the Deck plugin.

Nextcloud is an open-source, self-hosted productivity platform. A missing permission check in Nextcloud Deck before 1.2.9, 1.4.5 and 1.5.3 allows another authenticated users to access Deck cards of another user. It is recommended that the Nextcloud Deck App is upgraded to 1.2.9, 1.4.5 or 1.5.3. There are no known workarounds aside from upgrading.

Nextcloud Deck before 1.2.7, 1.4.1 suffers from an information disclosure vulnerability when searches for sharees utilize the lookup server by default instead of only the local Nextcloud server unless a global search has been explicitly chosen by the user.