Discourse-reactions is a plugin that allows user to add their reactions to the post. Data about a user's reaction notifications could be exposed. This vulnerability was patched in commit 2c26939.
https://github.com/discourse/discourse-reactions/security/advisories/GHSA-mq82-7v5x-rhv8
https://github.com/discourse/discourse-reactions/commit/2c26939395177730e492640d71aac68423be84fc