CVE-2026-55420

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.