CVE-2026-27454: Discourse

Medium severity, CVSS 5.3. EPSS: 1% chance of exploitation in the next 30 days.

Discourse is an open-source discussion platform. Prior to versions 2026.3.0-latest.1, 2026.2.1, and 2026.1.2, requesting /posts/:id.json?version=X bypassed authorization checks on post revisions. The display_post method called post.revert_to directly without verifying whether the revision was hidden or if the user had permission to view edit history. This meant hidden revisions (intentionally concealed by staff) could be read by any user by simply enumerating version numbers. Starting in versions 2026.3.0-latest.1, 2026.2.1, and 2026.1.2, Discourse looks up the PostRevision and call guardian.ensure_can_see! before reverting, consistent with how the /posts/:id/revisions/:revision endpoint already authorizes access. No known workarounds are available.

Affected products

• Discourse Discourse: from 2026.1.0, before 2026.1.2 (fixed in 2026.1.2); from 2026.2.0, before 2026.2.1 (fixed in 2026.2.1); version 2026.3.0 only

Published 2026-03-19. Last modified 2026-06-17.