CVE-2026-21386 — Private channel enumeration via /mute slash command

CVE-2026-21386

Private channel enumeration via /mute slash command PUBLISHED

Description (CNA)

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

Affected (CNA)

Vendor / product	Versions
Mattermost / Mattermost	affected 11.3.0 through 11.3.0; affected 11.2.0 through 11.2.2; affected 10.11.0 through 10.11.10; unaffected 11.4.0; unaffected 11.3.1; unaffected 11.2.3; unaffected 10.11.11

CWE

CWE-203

References

https://mattermost.com/security-updates

ADP enrichment

CISA-ADP

No English description supplied.

No references supplied.