Discourse Calendar adds the ability to create a dynamic calendar in the first post of a topic on Discourse. Uninvited users are able to gain access to private events by crafting a request to update their attendance. This problem is resolved in commit dfc4fa15f340189f177a1d1ab2cc94ffed3c1190. As a workaround, one may use post visibility to limit access.

Discourse Calendar adds the ability to create a dynamic calendar in the first post of a topic on the open-source discussion platform Discourse. Prior to version 0.4, event invitees created in topics in private categories or PMs (private messages) can be retrieved by anyone, even if they're not logged in. This problem is resolved in version 0.4 of the discourse-calendar plugin. While no known workaround is available, putting the site behind loginrequired will disallow this endpoint to be used by anonymous users, but logged in users can still get the list of invitees in the private topics.

Discourse-calendar is a plugin for the Discourse messaging platform which adds the ability to create a dynamic calendar in the first post of a topic. Members of private groups or public groups with private members can be listed by users, who can create and edit post events. This vulnerability only affects sites which have discourse post events enabled. This issue has been patched in commit ca5ae3e7e which will be included in future releases. Users unable to upgrade should disable the discourseposteventenabled setting to fully mitigate the issue. Also, it's possible to prevent regular users from using this vulnerability by removing all groups from the discourseposteventallowedongroups but note that moderators will still be able to use it.