{"dataType": "CVE_RECORD", "dataVersion": "5.2", "cveMetadata": {"cveId": "CVE-2026-8821", "assignerOrgId": "9302f53e-dde5-4bf3-b2f2-a83f91ac0eee", "state": "PUBLISHED", "assignerShortName": "Mattermost", "dateReserved": "2026-05-18T09:19:00.475Z", "datePublished": "2026-09-14T10:42:42.672Z", "dateUpdated": "2026-09-14T11:19:44.842Z"}, "containers": {"cna": {"affected": [{"defaultStatus": "unaffected", "product": "Mattermost", "vendor": "Mattermost", "versions": [{"lessThanOrEqual": "11.9.0", "status": "affected", "version": "11.9.0", "versionType": "semver"}, {"lessThanOrEqual": "11.8.4", "status": "affected", "version": "11.8.0", "versionType": "semver"}, {"lessThanOrEqual": "11.7.7", "status": "affected", "version": "11.7.0", "versionType": "semver"}, {"lessThanOrEqual": "10.11.22", "status": "affected", "version": "10.11.0", "versionType": "semver"}, {"version": "11.10.0", "status": "unaffected"}, {"version": "11.9.1", "status": "unaffected"}, {"version": "11.8.5", "status": "unaffected"}, {"version": "11.7.8", "status": "unaffected"}, {"version": "10.11.23", "status": "unaffected"}]}], "credits": [{"lang": "en", "type": "finder", "value": "ilent0"}], "descriptions": [{"lang": "en", "value": "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 arbitrary user to a restricted channel via the run owner field.. Mattermost Advisory ID: MMSA-2026-00677"}], "metrics": [{"cvssV3_1": {"attackVector": "NETWORK", "attackComplexity": "LOW", "privilegesRequired": "LOW", "userInteraction": "NONE", "scope": "UNCHANGED", "confidentialityImpact": "HIGH", "integrityImpact": "LOW", "availabilityImpact": "NONE", "version": "3.1", "vectorString": "CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:L/A:N", "baseSeverity": "HIGH", "baseScore": 7.1}, "format": "CVSS", "scenarios": [{"lang": "en", "value": "GENERAL"}]}], "problemTypes": [{"descriptions": [{"lang": "en", "type": "CWE", "description": "CWE-862: Missing Authorization", "cweId": "CWE-862"}]}], "references": [{"url": "https://mattermost.com/security-updates", "name": "MMSA-2026-00677", "tags": ["vendor-advisory"]}], "solutions": [{"value": "Update Mattermost to versions 11.10.0, 11.9.1, 11.8.5, 11.7.8, 10.11.23 or higher.", "lang": "en"}], "source": {"advisory": "MMSA-2026-00677", "defect": ["https://mattermost.atlassian.net/browse/MM-68695"], "discovery": "EXTERNAL"}, "title": "Playbooks run owner channel membership permission bypass", "providerMetadata": {"orgId": "9302f53e-dde5-4bf3-b2f2-a83f91ac0eee", "shortName": "Mattermost", "dateUpdated": "2026-09-14T10:42:42.672Z"}, "x_generator": {"engine": "cvelib 1.8.0"}}, "adp": [{"metrics": [{"other": {"type": "ssvc", "content": {"id": "CVE-2026-8821", "role": "CISA Coordinator", "options": [{"Exploitation": "none"}, {"Automatable": "no"}, {"Technical Impact": "partial"}], "version": "2.0.3", "timestamp": "2026-09-14T11:03:09.855978Z"}}}], "title": "CISA ADP Vulnrichment", "providerMetadata": {"orgId": "134c704f-9b21-4f2e-91b3-4a467353bcc0", "shortName": "CISA-ADP", "dateUpdated": "2026-09-14T11:19:44.842Z"}}]}}

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{"affected": [{"affectedData": [{"defaultStatus": "unaffected", "product": "Mattermost", "vendor": "Mattermost", "versions": [{"lessThanOrEqual": "11.9.0", "status": "affected", "version": "11.9.0", "versionType": "semver"}, {"lessThanOrEqual": "11.8.4", "status": "affected", "version": "11.8.0", "versionType": "semver"}, {"lessThanOrEqual": "11.7.7", "status": "affected", "version": "11.7.0", "versionType": "semver"}, {"lessThanOrEqual": "10.11.22", "status": "affected", "version": "10.11.0", "versionType": "semver"}, {"status": "unaffected", "version": "11.10.0"}, {"status": "unaffected", "version": "11.9.1"}, {"status": "unaffected", "version": "11.8.5"}, {"status": "unaffected", "version": "11.7.8"}, {"status": "unaffected", "version": "10.11.23"}]}], "source": "responsibledisclosure@mattermost.com"}], "cveTags": [], "descriptions": [{"lang": "en", "value": "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 arbitrary user to a restricted channel via the run owner field.. Mattermost Advisory ID: MMSA-2026-00677"}], "id": "CVE-2026-8821", "lastModified": "2026-09-14T11:17:06.153", "metrics": {"cvssMetricV31": [{"cvssData": {"attackComplexity": "LOW", "attackVector": "NETWORK", "availabilityImpact": "NONE", "baseScore": 7.1, "baseSeverity": "HIGH", "confidentialityImpact": "HIGH", "integrityImpact": "LOW", "privilegesRequired": "LOW", "scope": "UNCHANGED", "userInteraction": "NONE", "vectorString": "CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:L/A:N", "version": "3.1"}, "exploitabilityScore": 2.8, "impactScore": 4.2, "source": "responsibledisclosure@mattermost.com", "type": "Secondary"}]}, "published": "2026-09-14T11:17:06.153", "references": [{"source": "responsibledisclosure@mattermost.com", "url": "https://mattermost.com/security-updates"}], "sourceIdentifier": "responsibledisclosure@mattermost.com", "vulnStatus": "Received", "weaknesses": [{"description": [{"lang": "en", "value": "CWE-862"}], "source": "responsibledisclosure@mattermost.com", "type": "Secondary"}]}

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