{"id":"CVE-2026-9816","state":"PUBLISHED","title":"Insufficient server-side validation of board member role fields permits privilege escalation","description":"Mattermost versions 11.7.x <= 11.7.6, 10.11.x <= 10.11.21, 11.8.x <= 11.8.3 fail to validate BoardMember.Scheme* fields server-side on insert and archive-import paths which allows a board editor or non-guest team member to grant board admin to arbitrary users via POST /api/v2/boards/{boardID}/members and POST /api/v2/teams/{teamID}/archive/import.. Mattermost Advisory ID: MMSA-2026-00685","publishedAt":"2026-08-17T22:05:24.910Z","updatedAt":"2026-08-18T15:26:07.011Z","severity":{"score":8.3,"label":"High","version":"3.1","vector":"CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:H/A:H","source":"Mattermost"},"assigner":"Mattermost","products":["Mattermost Mattermost"],"affected":[{"vendor":"Mattermost","product":"Mattermost","defaultStatus":"unaffected","versions":[{"version":"11.7.0","status":"affected","lessThanOrEqual":"11.7.6","versionType":"semver"},{"version":"10.11.0","status":"affected","lessThanOrEqual":"10.11.21","versionType":"semver"},{"version":"11.8.0","status":"affected","lessThanOrEqual":"11.8.3","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"}]}],"references":["https://mattermost.com/security-updates"],"weaknesses":["CWE-863"],"ingestedAt":"2026-10-29T20:13:52.441Z","source":{"repository":"CVEProject/cvelistV5","path":"cves/2026/9xxx/CVE-2026-9816.json","commit":"556c9d3a8cd17e218bb8e452ba7cd619a384ff47"},"raw":{"dataType":"CVE_RECORD","dataVersion":"5.2","cveMetadata":{"cveId":"CVE-2026-9816","state":"PUBLISHED","datePublished":"2026-08-17T22:05:24.910Z","dateUpdated":"2026-08-18T15:26:07.011Z","assignerShortName":"Mattermost","assignerOrgId":"9302f53e-dde5-4bf3-b2f2-a83f91ac0eee","dateReserved":"2026-05-28T09:54:00.723Z"},"containers":{"cna":{"title":"Insufficient server-side validation of board member role fields permits privilege escalation","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 validate BoardMember.Scheme* fields server-side on insert and archive-import paths which allows a board editor or non-guest team member to grant board admin to arbitrary users via POST /api/v2/boards/{boardID}/members and POST /api/v2/teams/{teamID}/archive/import.. Mattermost Advisory ID: MMSA-2026-00685"}],"affected":[{"vendor":"Mattermost","product":"Mattermost","defaultStatus":"unaffected","versions":[{"version":"11.7.0","status":"affected","lessThanOrEqual":"11.7.6","versionType":"semver"},{"version":"10.11.0","status":"affected","lessThanOrEqual":"10.11.21","versionType":"semver"},{"version":"11.8.0","status":"affected","lessThanOrEqual":"11.8.3","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"}]}],"references":[{"url":"https://mattermost.com/security-updates","name":"MMSA-2026-00685","tags":["vendor-advisory"]}],"metrics":[{"cvssV3_1":{"attackVector":"NETWORK","attackComplexity":"LOW","privilegesRequired":"LOW","userInteraction":"NONE","scope":"UNCHANGED","confidentialityImpact":"LOW","integrityImpact":"HIGH","availabilityImpact":"HIGH","version":"3.1","vectorString":"CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:H/A:H","baseSeverity":"HIGH","baseScore":8.3},"format":"CVSS","scenarios":[{"lang":"en","value":"GENERAL"}]}],"problemTypes":[{"descriptions":[{"cweId":"CWE-863","lang":"en","type":"CWE","description":"CWE-863: Incorrect Authorization"}]}],"providerMetadata":{"shortName":"Mattermost","orgId":"9302f53e-dde5-4bf3-b2f2-a83f91ac0eee","dateUpdated":"2026-08-17T22:05:24.910Z"},"credits":[{"lang":"en","type":"finder","value":"kamil-sawicki"}],"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-2026-00685","defect":["https://mattermost.atlassian.net/browse/MM-69022"],"discovery":"EXTERNAL"},"x_generator":{"engine":"cvelib 1.8.0"}},"adp":[{"title":"CISA ADP Vulnrichment","metrics":[{"other":{"type":"ssvc","content":{"timestamp":"2026-08-18T15:23:50.527601Z","id":"CVE-2026-9816","options":[{"Exploitation":"none"},{"Automatable":"no"},{"Technical Impact":"partial"}],"role":"CISA Coordinator","version":"2.0.3"}}}],"providerMetadata":{"shortName":"CISA-ADP","orgId":"134c704f-9b21-4f2e-91b3-4a467353bcc0","dateUpdated":"2026-08-18T15:26:07.011Z"}}]}}}