{"id":"CVE-2026-18551","aliases":["EUVD-2026-102806","GHSA-rh7p-pp3q-6cf8"],"status":"published","title":"Mattermost guest account privilege escalation via member roles API","description":"Mattermost versions 11.10.x \u003c= 11.10.0, 11.7.x \u003c= 11.7.9, 11.9.x \u003c= 11.9.1, 11.8.x \u003c= 11.8.5 fail to validate the combination of guest and admin scheme roles which allows an authenticated attacker to escalate a guest account to team or channel admin via a crafted PUT request to the member roles API endpoint.. Mattermost Advisory ID: MMSA-2026-00752","severity":{"version":"3.1","score":6.5,"vector":"CVSS:3.1/AV:N/AC:L/PR:H/UI:N/S:U/C:H/I:H/A:N","level":"medium","assessor":"cna","from":"cve"},"epss":{"day":"2026-11-12","score":0.00222,"percentile":0.12937,"model":"v2026.06.15"},"facts":{"in_kev":false,"known_exploited":false,"public_exploit":false,"fix_available":false},"cwes":["CWE-863"],"published":"2026-10-16T06:56:51Z","modified":"2026-10-31T02:49:01Z","products":[{"vendor":"mattermost","product":"mattermost"},{"vendor":"mattermost","product":"mattermost_server"}],"references":[{"url":"https://mattermost.com/security-updates","tags":["vendor-advisory","Vendor Advisory","advisory"]},{"url":"https://nvd.nist.gov/vuln/detail/CVE-2026-18551","tags":["advisory"]},{"url":"https://github.com/advisories/GHSA-rh7p-pp3q-6cf8"},{"url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/18xxx/CVE-2026-18551.json","tags":["advisory"]}],"sources":{"cve":[{"id":"CVE-2026-18551","title":"Mattermost guest account privilege escalation via member roles API","description":"Mattermost versions 11.10.x \u003c= 11.10.0, 11.7.x \u003c= 11.7.9, 11.9.x \u003c= 11.9.1, 11.8.x \u003c= 11.8.5 fail to validate the combination of guest and admin scheme roles which allows an authenticated attacker to escalate a guest account to team or channel admin via a crafted PUT request to the member roles API endpoint.. Mattermost Advisory ID: MMSA-2026-00752","status":"published","published":"2026-10-16T06:56:51.996Z","modified":"2026-10-20T13:11:28.823Z","cvss":[{"version":"3.1","score":6.5,"vector":"CVSS:3.1/AV:N/AC:L/PR:H/UI:N/S:U/C:H/I:H/A:N","level":"medium","assessor":"cna"}],"cwes":["CWE-863"],"updated_at":"2026-11-02T14:20:12.60856Z"}],"euvd":[{"id":"EUVD-2026-102806","description":"Mattermost versions 11.10.x \u003c= 11.10.0, 11.7.x \u003c= 11.7.9, 11.9.x \u003c= 11.9.1, 11.8.x \u003c= 11.8.5 fail to validate the combination of guest and admin scheme roles which allows an authenticated attacker to escalate a guest account to team or channel admin via a crafted PUT request to the member roles API endpoint.. Mattermost Advisory ID: MMSA-2026-00752","status":"published","published":"2026-10-16T06:56:51Z","modified":"2026-10-20T13:11:28Z","cvss":[{"version":"3.1","score":6.5,"vector":"CVSS:3.1/AV:N/AC:L/PR:H/UI:N/S:U/C:H/I:H/A:N","level":"medium"}],"updated_at":"2026-11-02T16:59:44.419021Z"}],"ghsa":[{"id":"GHSA-rh7p-pp3q-6cf8","title":"Mattermost versions 11.10.x \u003c= 11.10.0, 11.7.x \u003c= 11.7.9, 11.9.x \u003c= 11.9.1, 11.8.x \u003c= 11.8.5 fail...","description":"Mattermost versions 11.10.x \u003c= 11.10.0, 11.7.x \u003c= 11.7.9, 11.9.x \u003c= 11.9.1, 11.8.x \u003c= 11.8.5 fail to validate the combination of guest and admin scheme roles which allows an authenticated attacker to escalate a guest account to team or channel admin via a crafted PUT request to the member roles API endpoint.. Mattermost Advisory ID: MMSA-2026-00752","status":"published","published":"2026-10-16T09:30:28Z","modified":"2026-10-16T09:30:28Z","cvss":[{"version":"3.1","score":6.5,"vector":"CVSS:3.1/AV:N/AC:L/PR:H/UI:N/S:U/C:H/I:H/A:N","level":"medium"}],"cwes":["CWE-863"],"updated_at":"2026-11-02T15:13:51.12467Z"}],"nvd":[{"id":"CVE-2026-18551","description":"Mattermost versions 11.10.x \u003c= 11.10.0, 11.7.x \u003c= 11.7.9, 11.9.x \u003c= 11.9.1, 11.8.x \u003c= 11.8.5 fail to validate the combination of guest and admin scheme roles which allows an authenticated attacker to escalate a guest account to team or channel admin via a crafted PUT request to the member roles API endpoint.. Mattermost Advisory ID: MMSA-2026-00752","status":"published","published":"2026-10-16T07:17:12.26Z","modified":"2026-10-29T18:00:27.977Z","cvss":[{"version":"3.1","score":6.5,"vector":"CVSS:3.1/AV:N/AC:L/PR:H/UI:N/S:U/C:H/I:H/A:N","level":"medium","assessor":"secondary"}],"cwes":["CWE-863"],"updated_at":"2026-11-02T14:12:59.751798Z"}],"osv":[{"id":"CVE-2026-18551","title":"Mattermost guest account privilege escalation via member roles API","description":"Mattermost versions 11.10.x \u003c= 11.10.0, 11.7.x \u003c= 11.7.9, 11.9.x \u003c= 11.9.1, 11.8.x \u003c= 11.8.5 fail to validate the combination of guest and admin scheme roles which allows an authenticated attacker to escalate a guest account to team or channel admin via a crafted PUT request to the member roles API endpoint.. Mattermost Advisory ID: MMSA-2026-00752","status":"published","published":"2026-10-16T06:56:51.996Z","modified":"2026-10-31T02:49:01.024955456Z","cvss":[{"version":"3.1","score":6.5,"vector":"CVSS:3.1/AV:N/AC:L/PR:H/UI:N/S:U/C:H/I:H/A:N","level":"medium"}],"cwes":["CWE-863"],"updated_at":"2026-11-02T15:44:58.024074Z"}]}}