CVSS Vector
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:N/A:N
Lifecycle Timeline
4Description
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
Analysis
CVE-2026-21386 is a security vulnerability (CVSS 4.3) that allows an authenticated team member. Remediation should follow standard vulnerability management procedures.
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Remediation
Within 30 days: Identify affected systems and apply vendor patches as part of regular patch cycle. Monitor vendor channels for patch availability.
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External POC / Exploit Code
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EUVD-2026-12437
GHSA-5mr9-crcg-8wh2