{"id":"CVE-2026-4274","aliases":["GHSA-g7fp-cqj5-x8hf","GO-2026-5393"],"url":"https://o3.security/vulnerability/CVE-2026-4274","summary":"Insufficient authorization in shared channel membership sync grants team-level access instead of channel-level access","details":"Mattermost versions 11.2.x <= 11.2.2, 10.11.x <= 10.11.10, 11.4.x <= 11.4.0, 11.3.x <= 11.3.1 fail to restrict team-level access when processing membership sync from a remote cluster, which allows a malicious remote cluster to grant a user access to an entire private team instead of only the shared channel via sending crafted membership sync messages that trigger team membership assignment. Mattermost Advisory ID: MMSA-2026-00574","published":"2026-03-26T10:43:24.611Z","modified":"2026-09-18T03:46:35.972379558Z","cvss":{"score":5.4,"severity":"MEDIUM","vector":"CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:L/A:N"},"epss":null,"cisaKev":null,"exploitsKnown":0,"affectedPackages":[{"ecosystem":"Go","name":"github.com/mattermost/mattermost/server/v8","fixedVersion":"11.4.1"},{"ecosystem":"Go","name":"github.com/mattermost/mattermost/server/v8","fixedVersion":"11.3.2"},{"ecosystem":"Go","name":"github.com/mattermost/mattermost/server/v8","fixedVersion":"11.2.3"},{"ecosystem":"Go","name":"github.com/mattermost/mattermost/server/v8","fixedVersion":"10.11.11"},{"ecosystem":"Go","name":"github.com/mattermost/mattermost/server/v8","fixedVersion":"8.0.0-20260217110922-b7d4a1f1f59b"}],"fix":null,"references":[{"type":"ADVISORY","url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/4xxx/CVE-2026-4274.json"},{"type":"ADVISORY","url":"https://mattermost.com/security-updates"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-4274"},{"type":"PACKAGE","url":"https://github.com/mattermost/mattermost"}],"provenance":{"sources":["OSV.dev","FIRST.org (EPSS)"],"lastVerified":"2026-09-18T03:46:35.972379558Z"}}