{"id":"CVE-2026-0999","aliases":["GHSA-3c9r-7f29-qp32","GO-2026-4520"],"url":"https://o3.security/vulnerability/CVE-2026-0999","summary":"Authentication bypass via userID login when email and username login are disabled","details":"Mattermost versions 11.1.x <= 11.1.2, 10.11.x <= 10.11.9, 11.2.x <= 11.2.1 fail to properly validate login method restrictions which allows an authenticated user to bypass SSO-only login requirements via userID-based authentication. Mattermost Advisory ID: MMSA-2025-00548","published":"2026-02-16T09:47:45.960Z","modified":"2026-08-12T03:51:17.934159Z","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":{"score":0.00179,"percentile":0.07711,"asOf":"2026-09-17"},"cisaKev":null,"exploitsKnown":0,"affectedPackages":[{"ecosystem":"Go","name":"github.com/mattermost/mattermost/server/v8","fixedVersion":"8.0.0-20251212052346-61651b0df7ea"},{"ecosystem":"Go","name":"github.com/mattermost/mattermost-server","fixedVersion":null},{"ecosystem":"Go","name":"github.com/mattermost/mattermost-server","fixedVersion":null},{"ecosystem":"Go","name":"github.com/mattermost/mattermost-server","fixedVersion":null},{"ecosystem":"Go","name":"github.com/mattermost/mattermost-server","fixedVersion":"5.3.2-0.20251212052346-61651b0df7ea"}],"fix":null,"references":[{"type":"ADVISORY","url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/0xxx/CVE-2026-0999.json"},{"type":"ADVISORY","url":"https://mattermost.com/security-updates"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-0999"}],"provenance":{"sources":["OSV.dev","FIRST.org (EPSS)"],"lastVerified":"2026-08-12T03:51:17.934159Z"}}