Discourse Calendar plugin adds the ability to create a dynamic calendar in the first post of a topic to Discourse. Rendering event names can be susceptible to XSS attacks. This vulnerability only affects sites which have modified or disabled Discourse’s default Content Security Policy. The issue is patched in version 0.5 of the Discourse Calendar plugin.
https://github.com/discourse/discourse-calendar/security/advisories/GHSA-rq37-8pf3-4xc8
https://github.com/discourse/discourse-calendar/commit/81e1c8e3c4c02276fb890da7e3f684259aeb685c