{"id":"CVE-2026-18223","title":"Mattermost invitation tokens not bound to invited email address allowing unauthorized team and private channel access","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 invited recipient's email address when redeeming team and guest invitation tokens, which allows an authenticated attacker t…","severity":"medium","cvss":5,"cvssVector":"CVSS:3.1/AV:N/AC:H/PR:H/UI:N/S:U/C:H/I:L/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"],"published":"2026-10-16","updated":"2026-10-16","sourceUpdated":"2026-10-16T07:12:39.911Z","source":"CVEORG","sourceUrl":"https://www.cve.org/CVERecord?id=CVE-2026-18223","references":[{"url":"https://mattermost.com/security-updates","label":"MMSA-2026-00747"}],"tags":["cve.org"],"ingestedAt":"2026-10-16T08:02:23.120Z","slug":"CVE-2026-18223","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 invited recipient's email address when redeeming team and guest invitation tokens, which allows an authenticated attacker to join a team or gain unauthorized access to private channels via a forwarded or leaked invitation link.. Mattermost Advisory ID: MMSA-2026-00747\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":28,"depthScoreParts":{"impact":27.5,"likelihood":0,"exploitation":0,"ransomware":0},"changes":[]}