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CVE-2026-21386GO-2026-4744GHSA-5MR9-CRCG-8WH2

Private channel enumeration via /mute slash command

Published
Last modified
published
Not listed in CISA KEV
Fix
Fixed in 10.11.11+incompatible, 11.2.3+incompatible, 11.3.1+incompatible, 8.0.0-20260130144323-5bb5261c72fa, 5.3.2-0.20260130144323-5bb5261c72fa, and 3 more
None on Exploit-DB, Metasploit or GitHub
  • Exploitation: none
  • Automatable: no
  • Technical impact: partial

Summary

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

Timeline

  1. CVE published
  2. CISA SSVC assessment

    Exploitation: none · Automatable: no · Technical impact: partial

  3. Record last updated

Affected versions

  • Mattermost Mattermost

    From 11.3.0 · through 11.3.0; From 11.2.0 · through 11.2.2; From 10.11.0 · through 10.11.10

  • github.com/mattermost/mattermost-serverGo

    From 10.11.0-rc1+incompatible · fixed in 10.11.11+incompatible; From 11.2.0-rc1+incompatible · fixed in 11.2.3+incompatible; From 11.3.0-rc1+incompatible · fixed in 11.3.1+incompatible

  • github.com/mattermost/mattermost-server/v5Go

    All versions

  • github.com/mattermost/mattermost-server/v6Go

    All versions

  • github.com/mattermost/mattermost/server/v8Go

    fixed in 8.0.0-20260130144323-5bb5261c72fa

  • github.com/mattermost/mattermost-serverGo

    fixed in 5.3.2-0.20260130144323-5bb5261c72fa

  • github.com/mattermost/mattermost-serverGo

    From 10.11.0-rc1 · fixed in 10.11.11

  • github.com/mattermost/mattermost-serverGo

    From 11.2.0-rc1 · fixed in 11.2.3

  • github.com/mattermost/mattermost-serverGo

    From 11.3.0-rc1 · fixed in 11.3.1

References 1

mattermost.com