Discourse is an open source discussion platform. Versions prior to 2025.12.2, 2026.1.1, and 2026.2.0 have an IDOR (Insecure Direct Object Reference) in ReviewableNotesController. When enable_category_group_moderation is enabled, a user belonging to a category moderation group can create or delete their own notes on any reviewable in the system, including reviewables in categories they do not moderate. The controller used an unscoped Reviewable.find and the ensure_can_see guard only checked whether the user could access the review queue in general, not whether they could access the specific reviewable. Only instances with enable_category_group_moderation enabled are affected. Staff users (admins/moderators) are not impacted as they already have access to all reviewables. The issue is patched in versions 2025.12.2, 2026.1.1, and 2026.2.0 by scoping the reviewable lookup through Reviewable.viewable_by(current_user). As a workaround, disable the enable_category_group_moderation site setting. This removes the attack surface as only staff users will have access to the review queue.
Weakness
The product performs an authorization check when an actor attempts to access a resource or perform an action, but it does not correctly perform the check.
Affected Software
| Name | Vendor | Start Version | End Version |
|---|---|---|---|
| Discourse | Discourse | * | 2025.12.0 (excluding) |
| Discourse | Discourse | 2026.1.0 (including) | 2026.1.1 (excluding) |
| Discourse | Discourse | 2026.2.0 (including) | 2026.2.0 (including) |
Potential Mitigations
- Divide the product into anonymous, normal, privileged, and administrative areas. Reduce the attack surface by carefully mapping roles with data and functionality. Use role-based access control (RBAC) [REF-229] to enforce the roles at the appropriate boundaries.
- Note that this approach may not protect against horizontal authorization, i.e., it will not protect a user from attacking others with the same role.
- Use a vetted library or framework that does not allow this weakness to occur or provides constructs that make this weakness easier to avoid.
- For example, consider using authorization frameworks such as the JAAS Authorization Framework [REF-233] and the OWASP ESAPI Access Control feature [REF-45].
- For web applications, make sure that the access control mechanism is enforced correctly at the server side on every page. Users should not be able to access any unauthorized functionality or information by simply requesting direct access to that page.
- One way to do this is to ensure that all pages containing sensitive information are not cached, and that all such pages restrict access to requests that are accompanied by an active and authenticated session token associated with a user who has the required permissions to access that page.