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CVE-2026-28759

nvd nist
Published: May 18, 2026Modified: Jun 17, 2026

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4.3
Vector
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:L/A:N
Exploitability: 2.8 / Impact: 1.4
Source: responsibledisclosure@mattermost.com (Secondary)

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 (3)

Mattermost
1 product
Mattermost Server
Configuration A
3 vulnerable
Vulnerable SoftwareAffected Versions
Mattermost
Mattermost Server
From 10.11.0 to 10.11.14
Mattermost Server
From 11.4.0 to 11.4.4
Mattermost Server
From 11.5.0 to 11.5.2

Related CWEs

CWE-863
Incorrect Authorization
The product performs an authorization check when an actor attempts to access a resource or perform an action, but it does not correctly perform the check. This allows attackers to bypass intended access restrictions.

References (1)

Source: responsibledisclosure@mattermost.com
Vendor Advisory

Timeline

No history available yet.