{"dataType": "CVE_RECORD", "dataVersion": "5.2", "cveMetadata": {"cveId": "CVE-2026-9859", "assignerOrgId": "9302f53e-dde5-4bf3-b2f2-a83f91ac0eee", "state": "PUBLISHED", "assignerShortName": "Mattermost", "dateReserved": "2026-05-28T15:58:29.723Z", "datePublished": "2026-08-17T22:06:26.318Z", "dateUpdated": "2026-08-17T22:06:26.318Z"}, "containers": {"cna": {"affected": [{"defaultStatus": "unaffected", "product": "Mattermost", "vendor": "Mattermost", "versions": [{"lessThanOrEqual": "11.7.6", "status": "affected", "version": "11.7.0", "versionType": "semver"}, {"lessThanOrEqual": "10.11.21", "status": "affected", "version": "10.11.0", "versionType": "semver"}, {"lessThanOrEqual": "11.8.3", "status": "affected", "version": "11.8.0", "versionType": "semver"}, {"version": "11.9.0", "status": "unaffected"}, {"version": "11.7.7", "status": "unaffected"}, {"version": "10.11.22", "status": "unaffected"}, {"version": "11.8.4", "status": "unaffected"}]}], "credits": [{"lang": "en", "type": "finder", "value": "kauasilvab14fb3"}], "descriptions": [{"lang": "en", "value": "Mattermost versions 11.7.x <= 11.7.6, 10.11.x <= 10.11.21, 11.8.x <= 11.8.3 fail to enforce PermissionManageBoardRoles on the channelId field of the batch endpoint, which allows an authenticated board editor to relink any board they can edit to an arbitrary channel via a crafted PATCH request. Mattermost Advisory ID: MMSA-2026-00686"}], "metrics": [{"cvssV3_1": {"attackVector": "NETWORK", "attackComplexity": "LOW", "privilegesRequired": "LOW", "userInteraction": "NONE", "scope": "UNCHANGED", "confidentialityImpact": "HIGH", "integrityImpact": "NONE", "availabilityImpact": "NONE", "version": "3.1", "vectorString": "CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:N", "baseSeverity": "MEDIUM", "baseScore": 6.5}, "format": "CVSS", "scenarios": [{"lang": "en", "value": "GENERAL"}]}], "problemTypes": [{"descriptions": [{"lang": "en", "type": "CWE", "description": "CWE-863: Incorrect Authorization", "cweId": "CWE-863"}]}], "references": [{"url": "https://mattermost.com/security-updates", "name": "MMSA-2026-00686", "tags": ["vendor-advisory"]}], "solutions": [{"value": "Update Mattermost to versions 11.9.0, 11.7.7, 10.11.22, 11.8.4 or higher.", "lang": "en"}], "source": {"advisory": "MMSA-2026-00686", "defect": ["https://mattermost.atlassian.net/browse/MM-69031"], "discovery": "EXTERNAL"}, "title": "Mattermost Boards plugin didn\u2019t enforce role-based authorization on board channel link allowing board editors to expose boards to arbitrary channels", "providerMetadata": {"orgId": "9302f53e-dde5-4bf3-b2f2-a83f91ac0eee", "shortName": "Mattermost", "dateUpdated": "2026-08-17T22:06:26.318Z"}, "x_generator": {"engine": "cvelib 1.8.0"}}}}

{}

{"affected": [{"affectedData": [{"defaultStatus": "unaffected", "product": "Mattermost", "vendor": "Mattermost", "versions": [{"lessThanOrEqual": "11.7.6", "status": "affected", "version": "11.7.0", "versionType": "semver"}, {"lessThanOrEqual": "10.11.21", "status": "affected", "version": "10.11.0", "versionType": "semver"}, {"lessThanOrEqual": "11.8.3", "status": "affected", "version": "11.8.0", "versionType": "semver"}, {"status": "unaffected", "version": "11.9.0"}, {"status": "unaffected", "version": "11.7.7"}, {"status": "unaffected", "version": "10.11.22"}, {"status": "unaffected", "version": "11.8.4"}]}], "source": "responsibledisclosure@mattermost.com"}], "cveTags": [], "descriptions": [{"lang": "en", "value": "Mattermost versions 11.7.x <= 11.7.6, 10.11.x <= 10.11.21, 11.8.x <= 11.8.3 fail to enforce PermissionManageBoardRoles on the channelId field of the batch endpoint, which allows an authenticated board editor to relink any board they can edit to an arbitrary channel via a crafted PATCH request. Mattermost Advisory ID: MMSA-2026-00686"}], "id": "CVE-2026-9859", "lastModified": "2026-08-17T22:17:27.343", "metrics": {"cvssMetricV31": [{"cvssData": {"attackComplexity": "LOW", "attackVector": "NETWORK", "availabilityImpact": "NONE", "baseScore": 6.5, "baseSeverity": "MEDIUM", "confidentialityImpact": "HIGH", "integrityImpact": "NONE", "privilegesRequired": "LOW", "scope": "UNCHANGED", "userInteraction": "NONE", "vectorString": "CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:N", "version": "3.1"}, "exploitabilityScore": 2.8, "impactScore": 3.6, "source": "responsibledisclosure@mattermost.com", "type": "Secondary"}]}, "published": "2026-08-17T22:17:27.343", "references": [{"source": "responsibledisclosure@mattermost.com", "url": "https://mattermost.com/security-updates"}], "sourceIdentifier": "responsibledisclosure@mattermost.com", "vulnStatus": "Received", "weaknesses": [{"description": [{"lang": "en", "value": "CWE-863"}], "source": "responsibledisclosure@mattermost.com", "type": "Secondary"}]}

{}

{"affected": [{"configurations": [{"platform": null, "status": "affected", "versions": {"scheme": "semver", "value": "[11.7.0,11.7.6]"}}, {"platform": null, "status": "affected", "versions": {"scheme": "semver", "value": "[10.11.0,10.11.21]"}}, {"platform": null, "status": "affected", "versions": {"scheme": "semver", "value": "[11.8.0,11.8.3]"}}, {"platform": null, "status": "unaffected", "versions": {"scheme": "semver", "value": "11.9.0"}}, {"platform": null, "status": "unaffected", "versions": {"scheme": "semver", "value": "11.7.7"}}, {"platform": null, "status": "unaffected", "versions": {"scheme": "semver", "value": "10.11.22"}}, {"platform": null, "status": "unaffected", "versions": {"scheme": "semver", "value": "11.8.4"}}], "enrichment": {"confidence": 100.0, "confidence_source": "matching", "scores": [{"score": 100.0, "source": "matching"}]}, "original": {"product": "Mattermost", "source": "cna", "vendor": "Mattermost"}, "product": "mattermost", "vendor": "mattermost"}], "created": "2026-08-17T23:30:04.672331+00:00", "updated": "2026-08-17T23:30:04.672361+00:00", "vendors": ["mattermost", "mattermost$PRODUCT$mattermost"]}