What’s Vulnerable › Vulnerabilities
CVE-2026-26973: Discourse doesn't scope reviewable notes to user-visible reviewables
- Severity: medium (CVSS 4.3 v3.1)
- Exploited in the wild: not listed in CISA KEV
- EPSS: 0.2% probability of exploitation in the next 30 days
- Public exploit or detection template: none known
- Published: 2026-02-26 · updated 2026-06-17
- Weakness: CWE-863
Description
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.
Affected products
- discourse: before 2025.12.0; from 2026.1.0 before 2026.1.1; 2026.2.0 — fixed in 2025.12.0, 2026.1.1
How to fix
Upgrade to a fixed version: discourse 2025.12.0, 2026.1.1. Check the vendor advisory for mitigations.
References
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