CVE-2026-28759

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

Score
CVSS 3.1 4.3 Medium
Status
Analyzed - responsibledisclosure@mattermost.com
Published
2026-05-18
Last modified
2026-10-14
Weaknesses
CWE-863

Affected products

References

 
 
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