{"id":"CVE-2026-18551","published":"2026-10-16T07:17:12.260","lastModified":"2026-10-17T04:16:52.380","description":"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 channel admin via a crafted PUT request to the member roles API endpoint.. Mattermost Advisory ID: MMSA-2026-00752","cvssScore":6.5,"cvssSeverity":"MEDIUM","cvssVector":"CVSS:3.1/AV:N/AC:L/PR:H/UI:N/S:U/C:H/I:H/A:N","cwes":["CWE-863"],"vendors":[],"products":[],"references":[{"url":"https://mattermost.com/security-updates","tags":[]}],"exploitRefs":[],"hasPoc":false,"ai":null}