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CVE-2026-28759

4.3 medium SSVC exploitation: none Analyzed
NVD · CVE.org

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

Fix

Patch, vendor advisory and mitigation references on NVD 1

Every line above is quoted from NVD, CISA, Microsoft, the vendor's own advisory or DISA; nothing is generated.

Change history 1

  1. First seenCVSS 4.3 · mattermostNVD modified 2026-10-14 20:10

Affected (CPE criteria) 1

  • cpe:2.3:a:mattermost:mattermost_server:*:*:*:*:*:*:*:*

References 1