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GHSA-8h9w-w78c-vvr3Published

Mattermost does not verify remote cluster channel access when processing shared channel membership removals

Exact source revision recorded 24 Oct 2026 13:19:41 UTC. It does not establish the source's current position. Latest evidence.

Recorded JSON

osv · GHSA-8h9w-w78c-vvr3

Published

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.

Source published
18 May 2026 09:31:47 UTC
Source modified
25 Jun 2026 19:56:34 UTC
Observed here
24 Oct 2026 13:19:41 UTC
Source terms
GitHub Advisory Database · CC-BY-4.0

Original source record · Cite this exact observation · Complete original publisher JSON

This view projects the publisher's source fields for reading; the original JSON retains additional fields and CVE enrichment containers. Attribution: osv · GitHub Advisory Database · CC-BY-4.0. Source text is retained; field grouping and change labels are provided by ChangeIntel.

CVSS_V3 · CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:L/A:N

Publisher rating · MODERATE

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Sources read 10 Nov 00:29 UTC · 275 of 275 readable · 273 fully read · documentation 469/469 current

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