CVE-2026-27454
Description
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.
How to fix
- discourse discourse2026.1.2, 2026.2.1 or later
Affected products
| Product | Affected versions | Fixed in |
|---|---|---|
| discourse discourse | 2026.1.0 ≤ v < 2026.1.2, 2026.2.0 ≤ v < 2026.2.1, 2026.3.0 | 2026.1.2, 2026.2.1 |
Check your version
Choose the product and enter the version you run to see whether it falls in the affected range.
Attack Surface Management
See the assets tied to your domains, the technologies they run and known vulnerabilities in one list.