Mattermost versions 11.3.x <= 11.3.0, 11.2.x <= 11.2.2, 10.11.x <= 10.11.10 fail to use consistent error responses when handling the /mute command which allows an authenticated team member to enumerate private channels they are not authorized to know about via differing error messages for nonexistent versus private channels. Mattermost Advisory ID: MMSA-2026-00588

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Advisories
Source ID Title
Github GHSA Github GHSA GHSA-5mr9-crcg-8wh2 Mattermost fails to use consistent error responses when handling the /mute command
Fixes

Solution

Update Mattermost to versions 11.4.0, 11.3.1, 11.2.3, 10.11.11 or higher.


Workaround

No workaround given by the vendor.

References
History

Wed, 18 Mar 2026 14:00:00 +0000

Type Values Removed Values Added
First Time appeared Mattermost mattermost Server
CPEs cpe:2.3:a:mattermost:mattermost_server:*:*:*:*:*:*:*:*
Vendors & Products Mattermost mattermost Server

Tue, 17 Mar 2026 10:00:00 +0000

Type Values Removed Values Added
First Time appeared Mattermost
Mattermost mattermost
Vendors & Products Mattermost
Mattermost mattermost

Mon, 16 Mar 2026 19:15:00 +0000

Type Values Removed Values Added
Metrics ssvc

{'options': {'Automatable': 'no', 'Exploitation': 'none', 'Technical Impact': 'partial'}, 'version': '2.0.3'}


Mon, 16 Mar 2026 15:15:00 +0000

Type Values Removed Values Added
Description Mattermost versions 11.3.x <= 11.3.0, 11.2.x <= 11.2.2, 10.11.x <= 10.11.10 fail to use consistent error responses when handling the /mute command which allows an authenticated team member to enumerate private channels they are not authorized to know about via differing error messages for nonexistent versus private channels. Mattermost Advisory ID: MMSA-2026-00588
Title Private channel enumeration via /mute slash command
Weaknesses CWE-203
References
Metrics cvssV3_1

{'score': 4.3, 'vector': 'CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:N/A:N'}


Projects

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cve-icon MITRE

Status: PUBLISHED

Assigner: Mattermost

Published:

Updated: 2026-03-16T18:39:14.064Z

Reserved: 2026-02-13T10:01:31.918Z

Link: CVE-2026-21386

cve-icon Vulnrichment

Updated: 2026-03-16T18:39:06.523Z

cve-icon NVD

Status : Analyzed

Published: 2026-03-16T15:16:20.927

Modified: 2026-03-18T13:53:15.357

Link: CVE-2026-21386

cve-icon Redhat

No data.

cve-icon OpenCVE Enrichment

Updated: 2026-03-17T09:52:44Z

Weaknesses