CVE-2026-31869
Description
Discourse is an open-source discussion platform. Prior to versions 2026.3.0-latest.1, 2026.2.1, and 2026.1.2, the ComposerController#mentions endpoint reveals hidden group membership to any authenticated user who can message the group. By supplying allowed_names referencing a hidden-membership group and probing arbitrary usernames, an attacker can infer membership based on whether user_reasons returns "private" for a given user. This bypasses group member-visibility controls. Versions 2026.3.0-latest.1, 2026.2.1, and 2026.1.2 contain a patch. To work around this issue, restrict the messageable policy of any hidden-membership group to staff or group members only, so untrusted users cannot reach the vulnerable code path.
AI Insight
LLM-synthesized narrative grounded in this CVE's description and references.
Affected products
5cpe:2.3:a:discourse:discourse:*:*:*:*:*:*:*:*+ 3 more
- cpe:2.3:a:discourse:discourse:*:*:*:*:*:*:*:*range: >=2026.1.0,<2026.1.2
- cpe:2.3:a:discourse:discourse:2026.3.0:*:*:*:latest:*:*:*
- (no CPE)range: <2026.3.0-latest.1, <2026.2.1, <2026.1.2
- (no CPE)range: >= 2026.1.0-latest, < 2026.1.2
Patches
Vulnerability mechanics
References
1- github.com/discourse/discourse/security/advisories/GHSA-5f9h-vp7v-7vq5nvdMitigationVendor Advisory
News mentions
0No linked articles in our index yet.