Executive brief
Discourse is an open-source discussion platform used to host community forums and private conversations. A flaw in its AI-powered moderation review system could allow a moderator to view private messages they were not a participant in, and potentially modify or delete content from those conversations. The vulnerability requires an authenticated moderator account and a pre-existing moderation review associated with a private message to exploit.
Technical details
The vulnerability is an access control bypass in the reviewable visibility filtering logic for private-message-associated AI reviewables. The viewable_by method failed to restrict private-message reviewables to the audience permitted to access the underlying topic, allowing any moderator to see and potentially act upon reviewables they should not have access to. Exploitation requires an authenticated moderator account and a pre-existing Discourse AI reviewable tied to a private message; the attack vector is network-based through the web interface.
Affected products
- Discourse Discourse prior to 2026.1.6, 2026.5.2, 2026.6.1, and 2026.7.0
Timeline
- 2026-09-24: disclosed
- 2026-01-06: patched: version 2026.1.6
- 2026-05-02: patched: version 2026.5.2
- 2026-06-01: patched: version 2026.6.1
- 2026-07-00: patched: version 2026.7.0