{"id":"CVE-2026-4274","state":"PUBLISHED","title":"Insufficient authorization in shared channel membership sync grants team-level access instead of channel-level access","description":"Mattermost versions 11.2.x <= 11.2.2, 10.11.x <= 10.11.10, 11.4.x <= 11.4.0, 11.3.x <= 11.3.1 fail to restrict team-level access when processing membership sync from a remote cluster, which allows a malicious remote cluster to grant a user access to an entire private team instead of only the shared channel via sending crafted membership sync messages that trigger team membership assignment. Mattermost Advisory ID: MMSA-2026-00574","publishedAt":"2026-03-26T10:43:24.611Z","updatedAt":"2026-03-26T13:58:41.567Z","severity":{"score":5.4,"label":"Medium","version":"3.1","vector":"CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:L/A:N","source":"Mattermost"},"assigner":"Mattermost","products":["Mattermost Mattermost"],"affected":[{"vendor":"Mattermost","product":"Mattermost","defaultStatus":"unaffected","versions":[{"version":"11.2.0","status":"affected","lessThanOrEqual":"11.2.2","versionType":"semver"},{"version":"10.11.0","status":"affected","lessThanOrEqual":"10.11.10","versionType":"semver"},{"version":"11.4.0","status":"affected","lessThanOrEqual":"11.4.0","versionType":"semver"},{"version":"11.3.0","status":"affected","lessThanOrEqual":"11.3.1","versionType":"semver"},{"version":"11.5.0","status":"unaffected"},{"version":"11.2.3","status":"unaffected"},{"version":"10.11.11","status":"unaffected"},{"version":"11.4.1","status":"unaffected"},{"version":"11.3.2","status":"unaffected"}]}],"references":["https://mattermost.com/security-updates"],"weaknesses":["CWE-863"],"ingestedAt":"2026-10-29T20:12:16.098Z","source":{"repository":"CVEProject/cvelistV5","path":"cves/2026/4xxx/CVE-2026-4274.json","commit":"556c9d3a8cd17e218bb8e452ba7cd619a384ff47"},"raw":{"dataType":"CVE_RECORD","dataVersion":"5.2","cveMetadata":{"cveId":"CVE-2026-4274","state":"PUBLISHED","datePublished":"2026-03-26T10:43:24.611Z","dateUpdated":"2026-03-26T13:58:41.567Z","assignerShortName":"Mattermost","assignerOrgId":"9302f53e-dde5-4bf3-b2f2-a83f91ac0eee","dateReserved":"2026-03-16T15:18:50.150Z"},"containers":{"cna":{"title":"Insufficient authorization in shared channel membership sync grants team-level access instead of channel-level access","descriptions":[{"lang":"en","value":"Mattermost versions 11.2.x <= 11.2.2, 10.11.x <= 10.11.10, 11.4.x <= 11.4.0, 11.3.x <= 11.3.1 fail to restrict team-level access when processing membership sync from a remote cluster, which allows a malicious remote cluster to grant a user access to an entire private team instead of only the shared channel via sending crafted membership sync messages that trigger team membership assignment. Mattermost Advisory ID: MMSA-2026-00574"}],"affected":[{"vendor":"Mattermost","product":"Mattermost","defaultStatus":"unaffected","versions":[{"version":"11.2.0","status":"affected","lessThanOrEqual":"11.2.2","versionType":"semver"},{"version":"10.11.0","status":"affected","lessThanOrEqual":"10.11.10","versionType":"semver"},{"version":"11.4.0","status":"affected","lessThanOrEqual":"11.4.0","versionType":"semver"},{"version":"11.3.0","status":"affected","lessThanOrEqual":"11.3.1","versionType":"semver"},{"version":"11.5.0","status":"unaffected"},{"version":"11.2.3","status":"unaffected"},{"version":"10.11.11","status":"unaffected"},{"version":"11.4.1","status":"unaffected"},{"version":"11.3.2","status":"unaffected"}]}],"references":[{"url":"https://mattermost.com/security-updates","name":"MMSA-2026-00574","tags":["vendor-advisory"]}],"metrics":[{"cvssV3_1":{"attackVector":"NETWORK","attackComplexity":"LOW","privilegesRequired":"LOW","userInteraction":"NONE","scope":"UNCHANGED","confidentialityImpact":"LOW","integrityImpact":"LOW","availabilityImpact":"NONE","version":"3.1","vectorString":"CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:L/A:N","baseSeverity":"MEDIUM","baseScore":5.4},"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":"2026-03-26T10:43:24.611Z"},"credits":[{"lang":"en","type":"finder","value":"daw10"}],"solutions":[{"value":"Update Mattermost to versions 11.5.0, 11.2.3, 10.11.11, 11.4.1, 11.3.2 or higher.","lang":"en"}],"source":{"advisory":"MMSA-2026-00574","defect":["https://mattermost.atlassian.net/browse/MM-67099"],"discovery":"EXTERNAL"},"x_generator":{"engine":"cvelib 1.8.0"}},"adp":[{"title":"CISA ADP Vulnrichment","metrics":[{"other":{"type":"ssvc","content":{"timestamp":"2026-03-26T13:58:33.420989Z","id":"CVE-2026-4274","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":"2026-03-26T13:58:41.567Z"}}]}}}