CVE-2026-21386

Private channel enumeration via /mute slash command

State: Published
Severity: 4.3 Medium
Published: Mar 16, 2026
Updated: Mar 16, 2026
Reserved: Feb 13, 2026

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

Scores

CVSS	Score	Vector	Source
3.1	4.3 Medium	CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:N/A:N	Mattermost

Weaknesses

CWE-203 Observable Discrepancy

Affected Products

Product	Versions
MattermostMattermost	11.3.0 through 11.3.0Affected 11.2.0 through 11.2.2Affected 10.11.0 through 10.11.10Affected 11.4.0Not affected 11.3.1Not affected 11.2.3Not affected 10.11.11Not affected

References

MMSA-2026-00588vendor-advisory

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