Discourse is an option source discussion platform. Prior to version 2.8.14 on the `stable` branch and version 2.9.0.beta15 on the `beta` and `tests-passed` branches, recipients of a group SMTP email could see the email addresses of all other users inside the group SMTP topic. Most of the time this is not an issue as they are likely already familiar with one another's email addresses. This issue is patched in versions 2.8.14 and 2.9.0.beta15. The fix is that someone sending emails out via group SMTP to non-staged users masks those emails with blind carbon copy (BCC). Staged users are ones that have likely only interacted with the group via email, and will likely include other people who were CC'd on the original email to the group. As a workaround, disable group SMTP for any groups that have it enabled.

Discourse Mermaid (discourse-mermaid-theme-component) allows users of Discourse, open-source forum software, to create graphs using the Mermaid syntax. Users of discourse-mermaid-theme-component version 1.0.0 who can create posts are able to inject arbitrary HTML on that post. The issue has been fixed on the `main` branch of the GitHub repository, with 1.1.0 named as a patched version. Admins can update the theme component through the admin UI. As a workaround, admins can temporarily disable discourse-mermaid-theme-component.

Discourse is an open-source discussion platform. In version 2.8.13 and prior on the `stable` branch and version 2.9.0.beta14 and prior on the `beta` and `tests-passed` branches, any authenticated user can create an unlisted topic. These topics, which are not readily available to other users, can take up unnecessary site resources. A patch for this issue is available in the `main` branch of Discourse. There are no known workarounds available.

discourse-bbcode is the official BBCode plugin for Discourse. Prior to commit 91478f5, CSS injection can occur when rendering content generated with the discourse-bccode plugin. This vulnerability only affects sites which have the discourse-bbcode plugin installed and enabled. This issue is patched in commit 91478f5. As a workaround, ensure that the Content Security Policy is enabled and monitor any posts that contain bbcode.

Discourse is an open-source discussion platform. Prior to version 2.8.13 of the `stable` branch and version 2.9.0.beta14 of the `beta` and `tests-passed` branches, unauthorized users may learn of the existence of hidden tags and that they have been applied to topics that they have access to. This issue is patched in version 2.8.13 of the `stable` branch and version 2.9.0.beta14 of the `beta` and `tests-passed` branches. As a workaround, use the `disable_email` site setting to disable all emails to non-staff users.

Discourse is an open-source messaging platform. In versions 2.8.10 and prior on the `stable` branch and versions 2.9.0.beta11 and prior on the `beta` and `tests-passed` branches, users composing malicious messages and navigating to drafts page could self-XSS. This vulnerability can lead to a full XSS on sites which have modified or disabled Discourse’s default Content Security Policy. This issue is patched in the latest stable, beta and tests-passed versions of Discourse.

Discourse is an open-source discussion platform. In stable versions prior to 2.8.12 and beta or tests-passed versions prior to 2.9.0.beta.13, under certain conditions, a user can see notifications for topics they no longer have access to. If there is sensitive information in the topic title, it will therefore have been exposed. This issue is patched in stable version 2.8.12, beta version 2.9.0.beta13, and tests-passed version 2.9.0.beta13. There are no workarounds available.

Discourse is an open-source discussion platform. Prior to version 2.9.0.beta13, users can post chat messages of an unlimited length, which can cause a denial of service for other users when posting huge amounts of text. Users should upgrade to version 2.9.0.beta13, where a limit has been introduced. No known workarounds are available.

Discourse is the an open source discussion platform. In some rare cases users redeeming an invitation can be added as a participant to several private message topics that they should not be added to. They are not notified of this, it happens transparently in the background. This issue has been resolved in commit `a414520742` and will be included in future releases. Users are advised to upgrade. Users are also advised to set `SiteSetting.max_invites_per_day` to 0 until the patch is installed.

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 `discourse_post_event_enabled` setting to fully mitigate the issue. Also, it's possible to prevent regular users from using this vulnerability by removing all groups from the `discourse_post_event_allowed_on_groups` but note that moderators will still be able to use it.