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.

INFO

Published Date :

2026-03-20T03:10:43.213Z

Last Modified :

2026-03-20T17:18:59.947Z

Source :

GitHub_M
AFFECTED PRODUCTS

The following products are affected by CVE-2026-31869 vulnerability.

Vendors Products
Discourse
  • Discourse
REFERENCES

Here, you will find a curated list of external links that provide in-depth information to CVE-2026-31869.

URL Resource
https://github.com/discourse/discourse/security/advisories/GHSA-5f9h-vp7v-7vq5 cve-icon cve-icon
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CVSS Vulnerability Scoring System

Detailed values of each vector for above chart.
Attack Vector
Attack Complexity
Attack Requirements
Privileges Required
User Interaction
VS Confidentiality
VS Integrity
VS Availability
SS Confidentiality
SS Integrity
SS Availability
Detailed values of each vector for above chart.
Attack Vector
Attack Complexity
Privileges Required
User Interaction
Scope
Confidentiality Impact
Integrity Impact
Availability Impact