CVEvulnerability

CVE-2026-31869

5.3 MEDIUM Published 2026-03-20 Modified 2026-06-17 Official page ↗
Status
Analyzed
Published
2026-03-20
Last modified
2026-06-17
Assigner
[email protected]
CVSS 4.0 ([email protected])
5.3 MEDIUM — CVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:N/VC:L/VI:N/VA:N/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X
CVSS 3.1 ([email protected])
4.3 MEDIUM — CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:N/A:N
Weaknesses
CWE-200, CWE-285, CWE-639

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.

Affected configurations

• discourse discourse (>= 2026.1.0 < 2026.1.2) • discourse discourse (>= 2026.2.0 < 2026.2.1) • discourse discourse 2026.3.0

Related

Weakness · CWE (3)

  • CWE-200 Exposure of Sensitive Information to an Unauthorized Actor weakness
  • CWE-285 Improper Authorization weakness
  • CWE-639 Authorization Bypass Through User-Controlled Key weakness

References