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VULNERABILITIES

CVE-2026-28759 Details

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

Metrics

CVSS 3.x Severity and Vector Strings:

CNA: [email protected]CVSS-B:4.3 MEDIUMVector:CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:L/A:N

References to Advisories, Solutions, and Tools

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URLSource(s)Tag(s)
https://mattermost.com/security-updates [email protected]Vendor Advisory

Weakness Enumeration

CWE-IDCWE NameSource
CWE-863Incorrect Authorization[email protected]

Affected Products

ProductVersions
mattermost mattermost server
>= 10.11.0, < 10.11.14
>= 11.4.0, < 11.4.4
>= 11.5.0, < 11.5.2

CPE

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

Remediation

  • No remediation found in references.

Change History

4 change records found show changes

QUICK INFO

CVE Dictionary Entry:
CVE-2026-28759
NVD Published Date:
May 18, 2026
NVD Last Modified:
Jun 17, 2026
Source:
[email protected]
CVE-2026-28759 Details - Not Deferred