{"dataType": "CVE_RECORD", "dataVersion": "5.2", "cveMetadata": {"cveId": "CVE-2026-28759", "assignerOrgId": "9302f53e-dde5-4bf3-b2f2-a83f91ac0eee", "state": "PUBLISHED", "assignerShortName": "Mattermost", "dateReserved": "2026-03-10T13:45:40.017Z", "datePublished": "2026-05-18T06:50:07.346Z", "dateUpdated": "2026-05-18T14:36:08.107Z"}, "containers": {"cna": {"affected": [{"defaultStatus": "unaffected", "product": "Mattermost", "vendor": "Mattermost", "versions": [{"lessThanOrEqual": "11.5.1", "status": "affected", "version": "11.5.0", "versionType": "semver"}, {"lessThanOrEqual": "10.11.13", "status": "affected", "version": "10.11.0", "versionType": "semver"}, {"lessThanOrEqual": "11.4.3", "status": "affected", "version": "11.4.0", "versionType": "semver"}, {"version": "11.6.0", "status": "unaffected"}, {"version": "11.5.2", "status": "unaffected"}, {"version": "10.11.14", "status": "unaffected"}, {"version": "11.4.4", "status": "unaffected"}]}], "credits": [{"lang": "en", "type": "finder", "value": "daw10"}], "descriptions": [{"lang": "en", "value": "Mattermost versions 11.5.x <= 11.5.1, 10.11.x <= 10.11.13, 11.4.x <= 11.4.3 fail to validate that a remote cluster has access to a channel before processing membership removal requests during shared channel membership sync, which allows a malicious remote cluster to remove any user from any channel, including private channels, via crafted membership sync messages targeting channels the remote cluster is not authorized to access. Mattermost Advisory ID: MMSA-2026-00576"}], "metrics": [{"cvssV3_1": {"attackVector": "NETWORK", "attackComplexity": "LOW", "privilegesRequired": "LOW", "userInteraction": "NONE", "scope": "UNCHANGED", "confidentialityImpact": "NONE", "integrityImpact": "LOW", "availabilityImpact": "NONE", "version": "3.1", "vectorString": "CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:L/A:N", "baseSeverity": "MEDIUM", "baseScore": 4.3}, "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-2026-00576", "tags": ["vendor-advisory"]}], "solutions": [{"value": "Update Mattermost to versions 11.6.0, 11.5.2, 10.11.14, 11.4.4 or higher.", "lang": "en"}], "source": {"advisory": "MMSA-2026-00576", "defect": ["https://mattermost.atlassian.net/browse/MM-67093"], "discovery": "EXTERNAL"}, "title": "Insufficient authorization in shared channel membership sync allows remote cluster to remove users from arbitrary channels", "providerMetadata": {"orgId": "9302f53e-dde5-4bf3-b2f2-a83f91ac0eee", "shortName": "Mattermost", "dateUpdated": "2026-05-18T06:50:07.346Z"}, "x_generator": {"engine": "cvelib 1.8.0"}}, "adp": [{"metrics": [{"other": {"type": "ssvc", "content": {"timestamp": "2026-05-18T14:35:53.724940Z", "id": "CVE-2026-28759", "options": [{"Exploitation": "none"}, {"Automatable": "no"}, {"Technical Impact": "partial"}], "role": "CISA Coordinator", "version": "2.0.3"}}}], "title": "CISA ADP Vulnrichment", "providerMetadata": {"orgId": "134c704f-9b21-4f2e-91b3-4a467353bcc0", "shortName": "CISA-ADP", "dateUpdated": "2026-05-18T14:36:08.107Z"}}]}}

{"dataType": "CVE_RECORD", "containers": {"adp": [{"title": "CISA ADP Vulnrichment", "metrics": [{"other": {"type": "ssvc", "content": {"id": "CVE-2026-28759", "role": "CISA Coordinator", "options": [{"Exploitation": "none"}, {"Automatable": "no"}, {"Technical Impact": "partial"}], "version": "2.0.3", "timestamp": "2026-05-18T14:35:53.724940Z"}}}], "providerMetadata": {"orgId": "134c704f-9b21-4f2e-91b3-4a467353bcc0", "shortName": "CISA-ADP", "dateUpdated": "2026-05-18T14:35:59.925Z"}}], "cna": {"title": "Insufficient authorization in shared channel membership sync allows remote cluster to remove users from arbitrary channels", "source": {"defect": ["https://mattermost.atlassian.net/browse/MM-67093"], "advisory": "MMSA-2026-00576", "discovery": "EXTERNAL"}, "credits": [{"lang": "en", "type": "finder", "value": "daw10"}], "metrics": [{"format": "CVSS", "cvssV3_1": {"scope": "UNCHANGED", "version": "3.1", "baseScore": 4.3, "attackVector": "NETWORK", "baseSeverity": "MEDIUM", "vectorString": "CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:L/A:N", "integrityImpact": "LOW", "userInteraction": "NONE", "attackComplexity": "LOW", "availabilityImpact": "NONE", "privilegesRequired": "LOW", "confidentialityImpact": "NONE"}, "scenarios": [{"lang": "en", "value": "GENERAL"}]}], "affected": [{"vendor": "Mattermost", "product": "Mattermost", "versions": [{"status": "affected", "version": "11.5.0", "versionType": "semver", "lessThanOrEqual": "11.5.1"}, {"status": "affected", "version": "10.11.0", "versionType": "semver", "lessThanOrEqual": "10.11.13"}, {"status": "affected", "version": "11.4.0", "versionType": "semver", "lessThanOrEqual": "11.4.3"}, {"status": "unaffected", "version": "11.6.0"}, {"status": "unaffected", "version": "11.5.2"}, {"status": "unaffected", "version": "10.11.14"}, {"status": "unaffected", "version": "11.4.4"}], "defaultStatus": "unaffected"}], "solutions": [{"lang": "en", "value": "Update Mattermost to versions 11.6.0, 11.5.2, 10.11.14, 11.4.4 or higher."}], "references": [{"url": "https://mattermost.com/security-updates", "name": "MMSA-2026-00576", "tags": ["vendor-advisory"]}], "x_generator": {"engine": "cvelib 1.8.0"}, "descriptions": [{"lang": "en", "value": "Mattermost versions 11.5.x <= 11.5.1, 10.11.x <= 10.11.13, 11.4.x <= 11.4.3 fail to validate that a remote cluster has access to a channel before processing membership removal requests during shared channel membership sync, which allows a malicious remote cluster to remove any user from any channel, including private channels, via crafted membership sync messages targeting channels the remote cluster is not authorized to access. Mattermost Advisory ID: MMSA-2026-00576"}], "problemTypes": [{"descriptions": [{"lang": "en", "type": "CWE", "cweId": "CWE-863", "description": "CWE-863: Incorrect Authorization"}]}], "providerMetadata": {"orgId": "9302f53e-dde5-4bf3-b2f2-a83f91ac0eee", "shortName": "Mattermost", "dateUpdated": "2026-05-18T06:50:07.346Z"}}}, "cveMetadata": {"cveId": "CVE-2026-28759", "state": "PUBLISHED", "dateUpdated": "2026-05-18T14:36:08.107Z", "dateReserved": "2026-03-10T13:45:40.017Z", "assignerOrgId": "9302f53e-dde5-4bf3-b2f2-a83f91ac0eee", "datePublished": "2026-05-18T06:50:07.346Z", "assignerShortName": "Mattermost"}, "dataVersion": "5.2"}

{"configurations": [{"nodes": [{"cpeMatch": [{"criteria": "cpe:2.3:a:mattermost:mattermost_server:*:*:*:*:*:*:*:*", "matchCriteriaId": "413D9405-79C3-4299-B0DC-40D9EE5CC717", "versionEndExcluding": "10.11.14", "versionStartIncluding": "10.11.0", "vulnerable": true}, {"criteria": "cpe:2.3:a:mattermost:mattermost_server:*:*:*:*:*:*:*:*", "matchCriteriaId": "CF171039-837A-4D23-87EB-F328AD04976C", "versionEndExcluding": "11.4.4", "versionStartIncluding": "11.4.0", "vulnerable": true}, {"criteria": "cpe:2.3:a:mattermost:mattermost_server:*:*:*:*:*:*:*:*", "matchCriteriaId": "726AD6AD-6C01-45BB-9115-B8209717A6D4", "versionEndExcluding": "11.5.2", "versionStartIncluding": "11.5.0", "vulnerable": true}], "negate": false, "operator": "OR"}]}], "cveTags": [], "descriptions": [{"lang": "en", "value": "Mattermost versions 11.5.x <= 11.5.1, 10.11.x <= 10.11.13, 11.4.x <= 11.4.3 fail to validate that a remote cluster has access to a channel before processing membership removal requests during shared channel membership sync, which allows a malicious remote cluster to remove any user from any channel, including private channels, via crafted membership sync messages targeting channels the remote cluster is not authorized to access. Mattermost Advisory ID: MMSA-2026-00576"}], "id": "CVE-2026-28759", "lastModified": "2026-05-18T19:17:19.280", "metrics": {"cvssMetricV31": [{"cvssData": {"attackComplexity": "LOW", "attackVector": "NETWORK", "availabilityImpact": "NONE", "baseScore": 4.3, "baseSeverity": "MEDIUM", "confidentialityImpact": "NONE", "integrityImpact": "LOW", "privilegesRequired": "LOW", "scope": "UNCHANGED", "userInteraction": "NONE", "vectorString": "CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:L/A:N", "version": "3.1"}, "exploitabilityScore": 2.8, "impactScore": 1.4, "source": "responsibledisclosure@mattermost.com", "type": "Secondary"}]}, "published": "2026-05-18T08:16:13.573", "references": [{"source": "responsibledisclosure@mattermost.com", "tags": ["Vendor Advisory"], "url": "https://mattermost.com/security-updates"}], "sourceIdentifier": "responsibledisclosure@mattermost.com", "vulnStatus": "Analyzed", "weaknesses": [{"description": [{"lang": "en", "value": "CWE-863"}], "source": "responsibledisclosure@mattermost.com", "type": "Secondary"}]}

{}

{"affected": [{"configurations": [{"platform": null, "status": "affected", "versions": {"scheme": "semver", "value": "[11.5.0,11.5.1]"}}, {"platform": null, "status": "affected", "versions": {"scheme": "semver", "value": "[10.11.0,10.11.13]"}}, {"platform": null, "status": "affected", "versions": {"scheme": "semver", "value": "[11.4.0,11.4.3]"}}, {"platform": null, "status": "unaffected", "versions": {"scheme": "semver", "value": "11.6.0"}}, {"platform": null, "status": "unaffected", "versions": {"scheme": "semver", "value": "11.5.2"}}, {"platform": null, "status": "unaffected", "versions": {"scheme": "semver", "value": "10.11.14"}}, {"platform": null, "status": "unaffected", "versions": {"scheme": "semver", "value": "11.4.4"}}], "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": "2026-05-18T09:30:22.003697+00:00", "updated": "2026-05-18T10:00:13.601368+00:00", "vendors": ["mattermost", "mattermost$PRODUCT$mattermost"]}