CVE-2026-21386

MEDIUM

Private channel enumeration via /mute slash command

Title source: cna
STIX 2.1

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

References (1)

Core 1
Core References
Vendor Advisory vendor-advisory
MMSA-2026-00588
https://mattermost.com/security-updates

Scores

CVSS v3 4.3
EPSS 0.0018
EPSS Percentile 8.1%
Attack Vector NETWORK
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:N/A:N

CISA SSVC

Vulnrichment
Exploitation none
Automatable no
Technical Impact partial

Details

CWE
CWE-203
Status published
Products (10)
mattermost/mattermost 0 - 8.0.0-20260130144323-5bb5261c72faGo
Mattermost/Mattermost 10.11.0 - 10.11.10
Mattermost/Mattermost 10.11.11
Mattermost/Mattermost 11.2.0 - 11.2.2
Mattermost/Mattermost 11.2.3
Mattermost/Mattermost 11.3.0
Mattermost/Mattermost 11.3.1
Mattermost/Mattermost 11.4.0
mattermost/mattermost-server 0 - 5.3.2-0.20260130144323-5bb5261c72faGo
mattermost/mattermost_server 10.11.0 - 10.11.11
Published Mar 16, 2026
Tracked Since Mar 16, 2026