Is CVE-2026-21386 actively exploited?

CVE-2026-21386 has no public evidence of in-the-wild exploitation as of 2026-03-18.

What is the CVSS score for CVE-2026-21386?

CVE-2026-21386 has a CVSS score of 4.3 (MEDIUM severity). Vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:N/A:N.

How do I patch CVE-2026-21386?

Patch guidance is available from mattermost security advisories. CVEDatabase generates AI-assisted remediation guidance on demand for CVE-2026-21386.

CVE-2026-21386 - remediation guidance & executive summary

Q: Which products are affected by CVE-2026-21386?

3 products: mattermost mattermost server, mattermost mattermost server, mattermost mattermost server.

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

CVSS Metrics

Vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:N/A:N
Attack Vector: network
Complexity: low
Privileges: low
User Action: none
Scope: unchanged
Confidentiality: low
Integrity: none
Availability: none
Weaknesses: CWE-203

Metadata

Primary Vendor: MATTERMOST
Published: 3/16/2026
Last Modified: 3/18/2026
Source: NIST NVD
Note: Verify all details with official vendor sources before applying patches.

Affected Products

mattermost : mattermost_servermattermost : mattermost_servermattermost : mattermost_server

Remediation Guidance

Executive Summary

Cite this page

CVE-2026-21386. CVEDatabase.com. Retrieved 1 May 2026. https://cvedatabase.com/cve/CVE-2026-21386

View on NIST NVD

CVE-2026-21386 vulnerability