{"id":"CVE-2026-8821","title":"Mattermost versions 11.9.x <= 11.9.0, 11.8.x <= 11.8.4, 11.7.x <= 11.7.7, 10.11.x <= 10.11.22 fail to validate channel member-management permission during playbook run creation, allowing an authenticated channel member to add an arbitrar…","summary":"Mattermost versions 11.9.x <= 11.9.0, 11.8.x <= 11.8.4, 11.7.x <= 11.7.7, 10.11.x <= 10.11.22 fail to validate channel member-management permission during playbook run creation, allowing an authenticated channel member to add an arbitrar…","severity":"high","cvss":7.1,"cvssVector":"CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:L/A:N","cwe":["CWE-862"],"vendor":"mattermost","product":"mattermost_server","affected":["mattermost_server >= 10.11.0, < 10.11.23","mattermost_server >= 11.7.0, < 11.7.8","mattermost_server >= 11.8.0, < 11.8.5","mattermost_server >= 11.9.0, < 11.9.1"],"patched":["mattermost_server 11.9.1"],"published":"2026-09-14","updated":"2026-10-07","sourceUpdated":"2026-10-07T15:43:05.857","source":"NVD","sourceUrl":"https://nvd.nist.gov/vuln/detail/CVE-2026-8821","references":[{"url":"https://mattermost.com/security-updates","label":"responsibledisclosure@mattermost.com"}],"tags":["nvd","cve.org"],"epss":0.0029,"epssPercentile":0.21422,"ssvc":{"exploitation":"none","automatable":"no","technicalImpact":"partial","timestamp":"2026-09-14T11:03:09.855978Z"},"ingestedAt":"2026-09-14T15:23:07.462Z","slug":"CVE-2026-8821","body":"## Overview\n\nMattermost versions 11.9.x <= 11.9.0, 11.8.x <= 11.8.4, 11.7.x <= 11.7.7, 10.11.x <= 10.11.22 fail to validate channel member-management permission during playbook run creation, allowing an authenticated channel member to add an arbitrary user to a restricted channel via the run owner field.. Mattermost Advisory ID: MMSA-2026-00677\n\n## Affected\n\n- `mattermost_server >= 10.11.0, < 10.11.23`\n- `mattermost_server >= 11.7.0, < 11.7.8`\n- `mattermost_server >= 11.8.0, < 11.8.5`\n- `mattermost_server >= 11.9.0, < 11.9.1`\n\n## Remediation\n\nUpgrade past the affected range:\n\n- `mattermost_server 11.9.1`","depth":"twilight","depthScore":39,"depthScoreParts":{"impact":39.1,"likelihood":0.1,"exploitation":0,"ransomware":0},"changes":[]}