{"id":"CVE-2026-18551","title":"Mattermost guest account privilege escalation via member roles API","summary":"Mattermost versions 11.10.x <= 11.10.0, 11.7.x <= 11.7.9, 11.9.x <= 11.9.1, 11.8.x <= 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 c…","severity":"medium","cvss":6.5,"cvssVector":"CVSS:3.1/AV:N/AC:L/PR:H/UI:N/S:U/C:H/I:H/A:N","cvssSource":"cna","cwe":["CWE-863"],"vendor":"Mattermost","product":"Mattermost","affected":["Mattermost >= 11.10.0 <= 11.10.0","Mattermost >= 11.7.0 <= 11.7.9","Mattermost >= 11.9.0 <= 11.9.1","Mattermost >= 11.8.0 <= 11.8.5"],"ssvc":{"exploitation":"none","automatable":"no","technicalImpact":"partial","timestamp":"2026-10-16T12:00:58.855163Z"},"published":"2026-10-16","updated":"2026-10-16","sourceUpdated":"2026-10-16T12:01:15.622Z","source":"CVEORG","sourceUrl":"https://www.cve.org/CVERecord?id=CVE-2026-18551","references":[{"url":"https://mattermost.com/security-updates","label":"MMSA-2026-00752"}],"tags":["cve.org"],"ingestedAt":"2026-10-16T08:02:23.126Z","slug":"CVE-2026-18551","body":"## Overview\n\nMattermost versions 11.10.x <= 11.10.0, 11.7.x <= 11.7.9, 11.9.x <= 11.9.1, 11.8.x <= 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\n\n## Affected\n\n- `Mattermost >= 11.10.0 <= 11.10.0`\n- `Mattermost >= 11.7.0 <= 11.7.9`\n- `Mattermost >= 11.9.0 <= 11.9.1`\n- `Mattermost >= 11.8.0 <= 11.8.5`\n\n## Remediation\n\nUpdate Mattermost to versions 11.11.0, 11.10.1, 11.7.10, 11.9.2, 11.8.6 or higher.","depth":"sunlit","depthScore":36,"depthScoreParts":{"impact":35.8,"likelihood":0,"exploitation":0,"ransomware":0},"changes":[]}