{"id":"CVE-2026-31869","aliases":["BIT-discourse-2026-31869","EUVD-2026-13496","GHSA-5f9h-vp7v-7vq5"],"status":"published","title":"Discourse: Composer mentions endpoint leaks hidden group membership through PM `allowed_names` check","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.","severity":{"version":"4.0","score":5.3,"vector":"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","level":"medium","assessor":"cna","from":"cve"},"epss":{"day":"2026-11-11","score":0.0019,"percentile":0.08695,"model":"v2026.06.15"},"facts":{"in_kev":false,"known_exploited":false,"public_exploit":false,"fix_available":true},"cwes":["CWE-200","CWE-285","CWE-639"],"published":"2026-03-20T03:10:43Z","modified":"2026-10-28T02:30:34Z","fixes":[{"ecosystem":"Bitnami","package":"discourse","fixed_in":["2026.1.2","2026.2.1","2026.3.0"],"sources":["osv"]}],"affected":[{"source":"osv","ecosystem":"Bitnami","package":"discourse","ranges":[{"type":"SEMVER","events":[{"introduced":"2026.1.0"},{"fixed":"2026.1.2"},{"introduced":"2026.2.0"},{"fixed":"2026.2.1"},{"introduced":"2026.3.0"},{"fixed":"2026.3.0"}]}]}],"products":[{"vendor":"discourse","product":"discourse"}],"references":[{"url":"https://github.com/discourse/discourse/security/advisories/GHSA-5f9h-vp7v-7vq5","tags":["x_refsource_CONFIRM","Mitigation","Vendor Advisory","advisory"]},{"url":"https://nvd.nist.gov/vuln/detail/CVE-2026-31869","tags":["web","advisory"]},{"url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/31xxx/CVE-2026-31869.json","tags":["advisory"]}],"sources":{"cve":[{"id":"CVE-2026-31869","title":"Discourse: Composer mentions endpoint leaks hidden group membership through PM `allowed_names` check","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.","status":"published","published":"2026-03-20T03:10:43.213Z","modified":"2026-03-20T17:18:59.947Z","cvss":[{"version":"4.0","score":5.3,"vector":"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","level":"medium","assessor":"cna"}],"cwes":["CWE-200","CWE-285","CWE-639"],"updated_at":"2026-11-02T14:19:51.277563Z"}],"euvd":[{"id":"EUVD-2026-13496","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.","status":"published","published":"2026-03-20T03:10:43Z","modified":"2026-03-20T17:18:59Z","cvss":[{"version":"4.0","score":5.3,"vector":"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","level":"medium"}],"updated_at":"2026-11-02T19:25:32.04432Z"}],"nvd":[{"id":"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.","status":"published","published":"2026-03-20T03:15:59.533Z","modified":"2026-06-17T10:34:40.02Z","cvss":[{"version":"4.0","score":5.3,"vector":"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","level":"medium","assessor":"secondary"},{"version":"3.1","score":4.3,"vector":"CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:N/A:N","level":"medium","assessor":"primary"}],"cwes":["CWE-200","CWE-285","CWE-639"],"updated_at":"2026-11-02T14:12:10.126802Z"}],"osv":[{"id":"CVE-2026-31869","title":"Discourse: Composer mentions endpoint leaks hidden group membership through PM `allowed_names` check","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.","status":"published","published":"2026-03-20T03:10:43.213Z","modified":"2026-10-28T02:30:34.543351337Z","cvss":[{"version":"4.0","score":5.3,"vector":"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","level":"medium"}],"cwes":["CWE-200","CWE-285","CWE-639"],"updated_at":"2026-11-02T15:45:01.218144Z"},{"id":"BIT-discourse-2026-31869","title":"Discourse: Composer mentions endpoint leaks hidden group membership through PM `allowed_names` check","description":"Discourse is an open-source discussion platform. Prior to versions 2026.3.0, 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, 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.","status":"published","published":"2026-03-27T07:10:33.91Z","modified":"2026-09-08T08:46:31.642409539Z","updated_at":"2026-11-02T15:28:29.152062Z"}]}}