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CVE PROGRAM SOURCE RECORD4.3 Medium

CVE-2026-28759

Insufficient authorization in shared channel membership sync allows remote cluster to remove users from arbitrary channels

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Status
Published
Published
Updated
Assigning organization
Mattermost

Description

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

Affected products

Version statuses are supplied by the assigning organization. Consult the original record for detailed ranges and platform conditions.

Mattermost Mattermost

Default version status: unaffected

  • 11.5.0 to ≤ 11.5.1affected
  • 10.11.0 to ≤ 10.11.13affected
  • 11.4.0 to ≤ 11.4.3affected
  • 11.6.0unaffected
  • 11.5.2unaffected
  • 10.11.14unaffected
  • 11.4.4unaffected

References