{"id":"CVE-2026-28759","sourceIdentifier":"responsibledisclosure@mattermost.com","published":"2026-05-18T08:16:13.573","lastModified":"2026-10-14T20:10:00.190","vulnStatus":"Analyzed","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"},{"lang":"es","value":"Las versiones de Mattermost 11.5.x hasta 11.5.1, 10.11.x hasta 10.11.13, 11.4.x hasta 11.4.3 fallan al validar que un clúster remoto tiene acceso a un canal antes de procesar las solicitudes de eliminación de membresía durante la sincronización de membresía de canales compartidos, lo que permite a un clúster remoto malicioso eliminar a cualquier usuario de cualquier canal, incluyendo canales privados, a través de mensajes de sincronización de membresía manipulados dirigidos a canales a los que el clúster remoto no está autorizado a acceder. ID de Aviso de Mattermost: MMSA-2026-00576"}],"affected":[{"source":"responsibledisclosure@mattermost.com","affectedData":[{"vendor":"Mattermost","product":"Mattermost","defaultStatus":"unaffected","versions":[{"version":"11.5.0","lessThanOrEqual":"11.5.1","versionType":"semver","status":"affected"},{"version":"10.11.0","lessThanOrEqual":"10.11.13","versionType":"semver","status":"affected"},{"version":"11.4.0","lessThanOrEqual":"11.4.3","versionType":"semver","status":"affected"},{"version":"11.6.0","status":"unaffected"},{"version":"11.5.2","status":"unaffected"},{"version":"10.11.14","status":"unaffected"},{"version":"11.4.4","status":"unaffected"}]}]}],"metrics":{"cvssMetricV31":[{"source":"responsibledisclosure@mattermost.com","type":"Secondary","cvssData":{"version":"3.1","vectorString":"CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:L/A:N","baseScore":4.3,"baseSeverity":"MEDIUM","attackVector":"NETWORK","attackComplexity":"LOW","privilegesRequired":"LOW","userInteraction":"NONE","scope":"UNCHANGED","confidentialityImpact":"NONE","integrityImpact":"LOW","availabilityImpact":"NONE"},"exploitabilityScore":2.8,"impactScore":1.4}],"ssvcV203":[{"source":"134c704f-9b21-4f2e-91b3-4a467353bcc0","ssvcData":{"timestamp":"2026-05-18T14:35:53.724940Z","id":"CVE-2026-28759","options":[{"exploitation":"none"},{"automatable":"no"},{"technicalImpact":"partial"}],"role":"CISA Coordinator","version":"2.0.3"}}]},"weaknesses":[{"source":"responsibledisclosure@mattermost.com","type":"Secondary","description":[{"lang":"en","value":"CWE-863"}]}],"configurations":[{"nodes":[{"operator":"OR","negate":false,"cpeMatch":[{"vulnerable":true,"criteria":"cpe:2.3:a:mattermost:mattermost_server:*:*:*:*:*:*:*:*","versionStartIncluding":"10.11.0","versionEndExcluding":"10.11.14","matchCriteriaId":"413D9405-79C3-4299-B0DC-40D9EE5CC717"},{"vulnerable":true,"criteria":"cpe:2.3:a:mattermost:mattermost_server:*:*:*:*:*:*:*:*","versionStartIncluding":"11.4.0","versionEndExcluding":"11.4.4","matchCriteriaId":"CF171039-837A-4D23-87EB-F328AD04976C"},{"vulnerable":true,"criteria":"cpe:2.3:a:mattermost:mattermost_server:*:*:*:*:*:*:*:*","versionStartIncluding":"11.5.0","versionEndExcluding":"11.5.2","matchCriteriaId":"726AD6AD-6C01-45BB-9115-B8209717A6D4"}]}]}],"references":[{"url":"https://mattermost.com/security-updates","source":"responsibledisclosure@mattermost.com","tags":["Vendor Advisory"]}]}