{"id":"CVE-2026-5139","aliases":["GHSA-2g8v-grq3-hq2g","GO-2026-6480"],"url":"https://o3.security/vulnerability/CVE-2026-5139","summary":"GitLab Plugin Allows Non-Admin Users to Modify Default Instance Configuration","details":"Mattermost versions 11.7.x <= 11.7.0, 11.6.x <= 11.6.2, 11.5.x <= 11.5.5, 10.11.x <= 10.11.17 fail to enforce administrator authorization on the {{setDefaultInstance}} call within the {{/gitlab connect}} command handler, which allows any authenticated user to overwrite the global default GitLab instance configuration via the {{/gitlab connect <instance-name>}} slash command.. Mattermost Advisory ID: MMSA-2026-00644","published":"2026-06-22T13:34:21.247Z","modified":"2026-10-28T02:30:29.361677164Z","cvss":{"score":5.4,"severity":"MEDIUM","vector":"CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:L/A:L"},"epss":{"score":0.00287,"percentile":0.21367,"asOf":"2026-09-17"},"cisaKev":null,"exploitsKnown":0,"affectedPackages":[{"ecosystem":"Go","name":"github.com/mattermost/mattermost-server","fixedVersion":"11.7.1"},{"ecosystem":"Go","name":"github.com/mattermost/mattermost-server","fixedVersion":"11.6.3"},{"ecosystem":"Go","name":"github.com/mattermost/mattermost-server","fixedVersion":"11.5.6"},{"ecosystem":"Go","name":"github.com/mattermost/mattermost-server","fixedVersion":"10.11.18"}],"fix":null,"references":[{"type":"ADVISORY","url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/5xxx/CVE-2026-5139.json"},{"type":"ADVISORY","url":"https://mattermost.com/security-updates"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-5139"},{"type":"PACKAGE","url":"https://github.com/mattermost/mattermost"}],"provenance":{"sources":["OSV.dev","FIRST.org (EPSS)"],"lastVerified":"2026-10-28T02:30:29.361677164Z"}}