Mattermost fails to use consistent error responses when handling the /mute command

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 nonexisten...

EUVD-2026-12437

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 nonexisten...

CVE-2026-21386

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 nonexisten...

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

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 nonexisten...

CVE-2026-21386

CVE-2026-21386 (Mattermost): The Mattermost server variants 11.3.x <= 11.3.0, 11.2.x <= 11.2.2, and 10.11.x

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

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 nonexisten...