Discourse vulnerabilities

Discourse before versions 2026.1.6, 2026.5.2, 2026.6.1, and 2026.7.0 leaked hidden or otherwise unviewable first-post content as an excerpt in the publicly-served Q&A (QAPage) JSON-LD structured data, exposing it to any unauthenticated visitor and to search-engine crawlers.

Discourse has an SQL injection vulnerability in the Data Explorer plugin, allowing arbitrary SQL execution via query parameters, even by unprivileged users.

Discourse, an open-source discussion platform, prior to versions 2026.1.6, 2026.5.2, 2026.6.1, and 2026.7.0 allowed an authenticated user to eavesdrop on private AI bot conversations through the AI bot reply stream.

Discourse prior to versions 2026.1.6, 2026.5.2, 2026.6.1, and 2026.7.0 in Onebox::DomainChecker.is_blocked? compares hostnames and SiteSetting.blocked_onebox_domains entries case-sensitively, allowing an attacker to bypass configured Onebox domain restrictions by changing character casing in a redirect target hostname.

In Discourse versions prior to 3.5.4, 2025.11.2, 2025.12.1, and 2026.1.0, permalinks pointing to access-restricted resources (private topics, categories, posts, or hidden tags) were redirecting users to URLs containing the resource slug, even when the user didn't have access to view the resource. This leaked potentially sensitive information (e.g., private topic titles) via the redirect Location header and the 404 page's search box.

Discourse, an open source discussion platform, contains a vulnerability in versions prior to 3.5.4, 2025.11.2, 2025.12.1, and 2026.1.0. The issue involves hostname validation in the FinalDestination component, which could allow bypassing SSRF protections under certain conditions.

Discourse is an open source discussion platform. In versions prior to 3.5.4, 2025.11.2, 2025.12.1, and 2026.1.0, some subscription endpoints lack proper checking for ownership before making changes. This issue is patched in versions 3.5.4, 2025.11.2, 2025.12.1, and 2026.1.0.

Prior to versions 2026.1.6, 2026.5.2, 2026.6.1, and 2026.7.0 in Discourse, an unauthenticated attacker could send a single request with a crafted color_scheme_id (or dark_scheme_id) cookie to inject arbitrary HTML into a Discourse page. Because the cookie value was rendered into a color scheme tag without escaping, the attacker could break out of the attribute and inject a tag that bypassed Discourse's nonce-based Content Security Policy, resulting in arbitrary JavaScript execution in visitors' browsers.

In Discourse prior to 2026.1.6, 2026.5.2, 2026.6.1, and 2026.7.1, on sites with category group moderation enabled, the review queue could include an excerpt (and permalink) of the private message attached to a flag, even when the reviewing category moderator was not a participant in that message. These notify_moderators flag messages are addressed only to moderators and, for core flags, to a category's moderation groups as they existed when the flag was raised, so a category group moderator could read flag-discussion content they were not authorized to see. This affects official plugins that create such messages and core flags raised before a moderator's group was granted moderation of the category. Only the confidentiality of a limited excerpt of these flag-related private messages is affected; no content can be modified or deleted.

In Discourse prior to 2026.1.6, 2026.5.2, 2026.6.1, and 2026.7.0, users who were allowed to view a group's activity, but were not permitted to see shared drafts, could still receive shared-draft entries through the group posts and group mentions endpoints. This could disclose shared-draft topic titles and post excerpt/content, resulting in an information disclosure of unpublished draft material.

Discourse prior to versions 2026.1.6, 2026.5.2, 2026.6.1, and 2026.7.0 contains a vulnerability in the discourse_templates endpoint that exposed hidden tag names. The DiscourseTemplates::TemplatesSerializer did not filter tags through the request Guardian, so it did not respect tag group permissions, allowing users to see tags they were not permitted to view.

Discourse has a stored XSS vulnerability in the rich text editor, where a chat-transcript username is rendered as HTML.

A vulnerability in Discourse prior to 2026.1.6, 2026.5.2, 2026.6.1, and 2026.7.0. The discourse-local-dates plugin rendered crafted local-date format data as HTML on sites with a modified or disabled default Content Security Policy.

Discourse, an open-source discussion platform, prior to 2026.1.7 allowed an authenticated user to submit specially formed URLs that bypassed the Onebox allowlist and embedded malicious content in a site. This issue is fixed in versions 2026.1.7, 2026.6.2, 2026.7.1, and 2026.8.0-latest.1.

Discourse prior to versions 2026.1.6, 2026.5.2, 2026.6.1, and 2026.7.0 allowed a low-privileged user to place crafted content in the moderation review queue that executed stored cross-site scripting when a moderator viewed it on a site with a modified or disabled default Content Security Policy. This issue is fixed in versions 2026.1.6, 2026.5.2, 2026.6.1, and 2026.7.0.

Discourse prior to version 2026.1.6 rendered previous and new value fields in the staff action log model without escaping, which could inject stored cross-site scripting into the staff interface.

Discourse prior to versions 2026.1.6, 2026.5.2, 2026.6.1, and 2026.7.0 in plugins/chat/lib/chat/onebox_handler.rb resolves Chat::Thread by route thread_id independently of the route channel_id before checking whether the user can preview the selected chat channel. An authenticated user can pair a public channel ID with a private thread ID in a /onebox.json request and obtain private thread message content.

Discourse prior to versions 2026.1.6, 2026.5.2, 2026.6.1, and 2026.7.0 in SiteSerializer.anonymous_default_navigation_menu_tags serializes tags from SiteSetting.default_navigation_menu_tags without applying DiscourseTagging.filter_visible for the anonymous viewer. An unauthenticated user can retrieve restricted tag names and descriptions through /site.json when those tags are limited by inaccessible categories, category tag groups, or tag-group permissions.

Discourse prior to versions 2026.1.6, 2026.5.2, 2026.6.1, and 2026.7.0 in TopicLink.extract_from, TopicLink.ensure_entry_for, and TopicLink.duplicate_lookup does not consistently enforce Guardian.can_see? checks when processing internal links. An authenticated user can submit links to restricted topics, private messages, or hidden posts and receive canonicalized slugs or titles in the composer_messages duplicate_lookup response even though the targets are not visible to that user.

Discourse prior to versions 2026.1.7, 2026.6.2, 2026.7.1, and 2026.8.0-latest.1 has HTML injection in PrettyText.format_for_email because cooked attribute values are reparsed as markup. Crafted Vimeo iframe sources, secure-upload URLs or dimensions, and hashtag data-slug values can cause decoded attribute text to be reinterpreted as HTML. The vulnerable conversion also fails to strictly validate the Vimeo iframe host and path, allowing non-Vimeo allowlisted iframes to be converted.

In Discourse prior to versions 2026.6.0, 2026.5.1, 2026.4.2, and 2026.1.5, post revisions hidden from regular users could be leaked through visible diffs on adjacent revisions serialized by PostRevisionSerializer.

In Discourse prior to versions 2026.6.0, 2026.5.1, 2026.4.2, and 2026.1.5, a topic featured link was not sufficiently normalized and escaped before being rendered in the topic list. This allowed a user who can set a featured link to inject JavaScript when default Content Security Policy protections were modified or disabled.

In Discourse prior to versions 2026.6.0, 2026.5.1, 2026.4.2, and 2026.1.5, a malicious second factor name on an attacker-controlled account was not escaped in the delete confirmation dialog, allowing stored cross-site scripting when an administrator impersonated that account.

In Discourse prior to versions 2026.6.0, 2026.5.1, 2026.4.2, and 2026.1.5, insufficient SVG sanitization in upload and user avatar handling could lead to cross-site scripting when a user visited specific URLs that are not normally part of community browsing.

In Discourse prior to versions 2026.6.0, 2026.5.1, 2026.4.2, and 2026.1.5, the AWS SES bounce webhook verified SNS message signatures but did not bind them to trusted TopicArn values, allowing any AWS account holder to send forged Bounce notifications that revoke a targeted user email.

In Discourse prior to versions 2026.6.0, 2026.5.1, 2026.4.2, and 2026.1.5, restricted tag and tag-group names attached to publicly readable categories as allowed_tags, allowed_tag_groups, or required tag groups could leak to anonymous and unauthorized users through category and group endpoints.

In Discourse prior to versions 2026.6.0, 2026.5.1, 2026.4.2, and 2026.1.5, regular users could route direct S3 multipart uploads through ExternalUploadManager into the admin backup store.

In Discourse prior to versions 2026.6.0, 2026.5.1, 2026.4.2, and 2026.1.5, the pull_hotlinked_images function could expose secure uploads if an attacker knew the secured upload URL and the secure_uploads site setting was enabled.

A vulnerability in Discourse prior to versions 2026.6.0, 2026.5.1, 2026.4.2, and 2026.1.5 allowed EventSerializer to expose invited group names, sample invitees, and attendance statistics to users who could view the topic but were not entitled to view the private event invitee list.

In Discourse prior to versions 2026.6.0, 2026.5.1, 2026.4.2, and 2026.1.5, the signup flow allowed newly registered users to set primary_group_id and gain whisper-group privileges without legitimate group membership on sites with whispers_allowed_groups configured.

In Discourse versions prior to 2026.6.0, 2026.5.1, 2026.4.2, and 2026.1.5, under certain non-default configurations, processing of PDF uploads could be exploited to achieve remote code execution (RCE) on the server. The vulnerability is patched in the mentioned versions.

Discourse is an open-source discussion platform with a vulnerability in versions from 2026.1.0 to before 2026.1.4, from 2026.3.0 to before 2026.3.1, and from 2026.4.0 to before 2026.4.1. The DetailedTagSerializer#tag_group_names function returned all tag groups a tag belonged to without considering the user's visibility, allowing anonymous and unprivileged users to access the names of tag groups restricted to specific user groups.

Discourse is an open-source discussion platform that has a vulnerability in versions from 2026.1.0 to before 2026.1.4, from 2026.3.0 to before 2026.3.1, and from 2026.4.0 to before 2026.4.1. The MessageBus.publish call for /web_hook_events/<id> in Jobs::RedeliverWebHookEvents did not pass group_ids, allowing any authenticated user (or anonymous user when login_required is disabled) to access the channel.

Discourse, a discussion platform, has a path traversal vulnerability in backup handling that allows an authenticated administrator on one site in a multisite deployment to access backup files of another site. This issue affects versions from 2026.1.0 to before 2026.1.4, from 2026.3.0 to before 2026.3.1, and from 2026.4.0 to before 2026.4.1.

Discourse is an open-source discussion platform with a vulnerability in versions from 2026.1.0 to before 2026.1.4, from 2026.3.0 to before 2026.3.1, and from 2026.4.0 to before 2026.4.1. Chat events for public category channels are published to MessageBus without proper permission scoping, allowing subscribers without chat enabled to receive chat message payloads in real time.

There is a vulnerability in the Discourse discussion platform that allows authenticated users to access hidden parent post content by using the AI 'explain' function on a reply to that post. This issue affects versions from 2026.1.0 to before 2026.1.4, from 2026.3.0 to before 2026.3.1, and from 2026.4.0 to before 2026.4.1.

Discourse is an open-source discussion platform where group owners, who are not necessarily admins or moderators, can view SMTP credentials in plaintext. This affects versions from 2026.1.0 to before 2026.1.4, from 2026.3.0 to before 2026.3.1, and from 2026.4.0 to before 2026.4.1.

A vulnerability in the Discourse discussion platform allows authenticated users outside the configured groups to post into staff-only whisper channels. This issue affects versions from 2026.1.0 to before 2026.1.4, from 2026.3.0 to before 2026.3.1, and from 2026.4.0 to before 2026.4.1.

Discourse is an open-source discussion platform that has a bug in the serialization of the :name attribute in GroupPostSerializer. The issue is that the incorrectly named predicate include_user_long_name? was never called, resulting in object.user.name always being serialized regardless of SiteSetting.enable_names.

Discourse is an open-source discussion platform with a vulnerability in versions from 2026.1.0 to before 2026.1.4, from 2026.3.0 to before 2026.3.1, and from 2026.4.0 to before 2026.4.1. The ReviewableQueuedPostSerializer unconditionally included payload["raw_email"] for posts arriving via email, allowing moderation group members to access the full email source without proper permissions.

Discourse is an open-source discussion platform that, in versions from 2026.1.0 to before 2026.1.4, from 2026.3.0 to before 2026.3.1, and from 2026.4.0 to before 2026.4.1, discloses whisper translation audit logs through bot debug endpoints. This issue has been patched in versions 2026.1.4, 2026.3.1, 2026.4.1, and 2026.5.0-latest.1.

Discourse prior to versions 2026.1.4, 2026.3.1, 2026.4.1, and 2026.5.0-latest.1 contains a vulnerability in the discourse-subscriptions plugin that allows users to gain access to subscription-gated groups without completing payment.

Discourse versions prior to 2026.1.4, 2026.3.1, 2026.4.1 and 2026.5.0-latest.1 allow an authenticated user to read the name and structured content of form templates intended exclusively for categories they are not authorized to access.

Discourse prior to versions 2026.1.4, 2026.3.1, 2026.4.1 and 2026.5.0-latest.1 caches outdated AI summaries that can leak removed content to anonymous and unprivileged users.

Discourse, an open-source discussion platform, has a vulnerability that exposes staged user custom fields and usernames on public invite pages without email verification. This affects versions from 2026.1.0-latest to before 2026.1.3, 2026.2.0-latest to before 2026.2.2, and 2026.3.0-latest to before 2026.3.0.

Discourse versions from 2026.1.0 to before 2026.1.3, 2026.2.0 to before 2026.2.2, and 2026.3.0 to before 2026.3.0 have an authorization bypass vulnerability. Unauthenticated or unauthorized users can view staff-only tags and associated data.

Discourse, an open-source discussion platform, has a vulnerability in a sentiment analytics endpoint. An authenticated moderator-level user can retrieve post content, topic titles, and usernames from unauthorized categories. The issue is fixed in versions 2026.1.3, 2026.2.2, and 2026.3.0.

An authorization bypass in Discourse's Category Chatables controller allows moderators to get information about hidden groups and user counts.

Discourse has a vulnerability in the group email settings test endpoint that allows initiating outbound connections to arbitrary hosts and ports. The endpoint was accessible to non-staff group owners.

Discourse versions from 2026.1.0 to before 2026.1.3, 2026.2.0 to before 2026.2.2, and 2026.3.0-latest to before 2026.3.0 allow a user to purchase a lower tier subscription but gain benefits associated with a higher tier subscription.