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

> CVE-2026-21386: Private channel enumeration via /mute slash command. CVSS 4.3 (CVSS 3.1).

Canonical: https://rewindex.com/cve/CVE-2026-21386
Last updated: 2026-06-17T10:18:36Z

- Published: 2026-03-16 14:51 UTC · Updated: 2026-06-17 10:18 UTC · Assigner: Mattermost
- CVSS: 4.3 (CVSS 3.1) · Severity: Medium · Vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:N/A:N
- EPSS: 0.19%, 8th percentile (scored 2026-10-25)
- CISA KEV: no
- CWE: CWE-203

## 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

## Affected vendors and products

- Mattermost: Mattermost

## Tracked companies

- [Mattermost](https://rewindex.com/company/mattermost.md)

## References

- [CVE record on cve.org](https://www.cve.org/CVERecord?id=CVE-2026-21386)
- [NVD entry](https://nvd.nist.gov/vuln/detail/CVE-2026-21386)
- [https://mattermost.com/security-updates](https://mattermost.com/security-updates)

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_Sources: CVE records from the CVE Program (cve.org). CVE® is a registered trademark of The MITRE Corporation. (https://www.cve.org/) This product uses data from the NVD API but is not endorsed or certified by the NVD. (https://nvd.nist.gov/) Known Exploited Vulnerabilities catalog from CISA. (https://www.cisa.gov/known-exploited-vulnerabilities-catalog) EPSS scores from FIRST (Exploit Prediction Scoring System). (https://www.first.org/epss/)_


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Canonical: https://rewindex.com/cve/CVE-2026-21386 · Markdown: https://rewindex.com/cve/CVE-2026-21386.md · JSON: https://rewindex.com/api/v1/cves/CVE-2026-21386 · Data licensed CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/) · Generated 2026-10-26T03:11:46.255Z