Vulnerability from bitnami_vulndb
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.
{
"affected": [
{
"package": {
"ecosystem": "Bitnami",
"name": "discourse",
"purl": "pkg:bitnami/discourse"
},
"ranges": [
{
"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"
}
],
"type": "SEMVER"
}
],
"severity": [
{
"score": "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",
"type": "CVSS_V4"
}
]
}
],
"aliases": [
"CVE-2026-31869"
],
"database_specific": {
"cpes": [
"cpe:2.3:a:discourse:discourse:*:*:*:*:*:*:*:*"
],
"severity": "Medium"
},
"details": "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.",
"id": "BIT-discourse-2026-31869",
"modified": "2026-09-08T08:34:36.952Z",
"published": "2026-03-27T07:10:33.910Z",
"references": [
{
"type": "ADVISORY",
"url": "https://github.com/discourse/discourse/security/advisories/GHSA-5f9h-vp7v-7vq5"
},
{
"type": "WEB",
"url": "https://nvd.nist.gov/vuln/detail/CVE-2026-31869"
}
],
"schema_version": "1.6.2",
"summary": "Discourse: Composer mentions endpoint leaks hidden group membership through PM `allowed_names` check"
}
Sightings
| Author | Source | Type | Date | Other |
|---|
Nomenclature
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- Not confirmed: The user expressed doubt about the validity of the vulnerability.
- Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.
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