{"id":"EUVD-2026-30738","enisaUuid":"5d2e75b2-7400-3c5f-bb95-383aeff1b061","description":"Mattermost versions 11.5.x \u003c\u003d 11.5.1, 10.11.x \u003c\u003d 10.11.13, 11.4.x \u003c\u003d 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","datePublished":"May 18, 2026, 6:50:07 AM","dateUpdated":"May 18, 2026, 2:36:08 PM","baseScore":4.3,"baseScoreVersion":"3.1","baseScoreVector":"CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:L/A:N","references":"https://mattermost.com/security-updates\n","aliases":"CVE-2026-28759\nGHSA-8h9w-w78c-vvr3\n","assigner":"Mattermost","epss":0.15,"enisaIdProduct":[{"id":"23825cd3-dedc-386a-99d3-460dd4f49a44","product":{"name":"Mattermost","vendor":{"name":"Mattermost"}},"product_version":"11.4.0 ≤11.4.3"},{"id":"3e3ea409-5e83-324c-b9c4-a6ed163d583c","product":{"name":"Mattermost","vendor":{"name":"Mattermost"}},"product_version":"10.11.0 ≤10.11.13"},{"id":"512e13c8-6977-3b8b-9943-374e2c6ee9b4","product":{"name":"Mattermost","vendor":{"name":"Mattermost"}},"product_version":"11.5.0 ≤11.5.1"}],"enisaIdVendor":[{"id":"20b4b459-fb99-3768-95c6-9c7048d561d2","vendor":{"name":"Mattermost"}}],"enisaIdVulnerability":[{"id":"17232025-a297-3a08-8a8a-abaa77fa631d","vulnerability":{"id":"GHSA-8h9w-w78c-vvr3","description":"Mattermost does not verify remote cluster channel access when processing shared channel membership removals","datePublished":"May 18, 2026, 9:31:47 AM","dateUpdated":"Jun 1, 2026, 3:48:10 PM","baseScore":0.0,"references":"https://nvd.nist.gov/vuln/detail/CVE-2026-28759\nhttps://github.com/mattermost/mattermost/commit/8738f8c4b3d42b2b687a6231e72f313357a2e891\nhttps://github.com/mattermost/mattermost\nhttps://mattermost.com/security-updates\n","enisa_id":"EUVD-2026-30738\n","aliases":"CVE-2026-28759\nGHSA-8h9w-w78c-vvr3\n","epss":0.0,"dataProcessed":"Nov 1, 2026, 2:00:21 AM","vulnerabilityProduct":[],"vulnerabilityVendor":[]}},{"id":"8d113338-dacb-37d4-addd-149833156c72","vulnerability":{"id":"CVE-2026-28759","description":"Mattermost versions 11.5.x \u003c\u003d 11.5.1, 10.11.x \u003c\u003d 10.11.13, 11.4.x \u003c\u003d 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","datePublished":"May 18, 2026, 6:50:07 AM","dateUpdated":"May 18, 2026, 2:36:08 PM","status":"PUBLISHED","baseScore":4.3,"baseScoreVersion":"3.1","baseScoreVector":"CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:L/A:N","references":"https://mattermost.com/security-updates\n","enisa_id":"EUVD-2026-30738\n","assigner":"Mattermost","epss":0.15,"dataProcessed":"Nov 7, 2026, 7:24:07 AM","vulnerabilityProduct":[{"id":"1b5de59a-b445-3532-95f5-331a7ca9cadb","product":{"name":"Mattermost","vendor":{"name":"Mattermost"}},"product_version":"11.5.0 ≤11.5.1"},{"id":"7206abf9-38a2-32e1-bcf7-8bdd3679681b","product":{"name":"Mattermost","vendor":{"name":"Mattermost"}},"product_version":"10.11.0 ≤10.11.13"},{"id":"936294de-3027-31a7-976f-e34b5e24f902","product":{"name":"Mattermost","vendor":{"name":"Mattermost"}},"product_version":"11.4.0 ≤11.4.3"}],"vulnerabilityVendor":[{"id":"a0bb24d6-bd21-3b15-97cc-b2f8dfbb91f6","vendor":{"name":"Mattermost"}}]}}],"enisaIdAdvisory":[]}