CVE-2026-21386

Name: CVE-2026-21386
Creator: NVD / NIST
Published: 2026-03-16T15:16:20.927+00:00
License: https://creativecommons.org/publicdomain/zero/1.0/

MEDIUMCVSS 4.3/10EPSS 0.18%

Last modified Jun 17, 2026

CVE-2026-21386 is a medium-severity vulnerability rated 4.3/10 on the CVSS scale. 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. EPSS estimates a 0.18% chance of exploitation in the next 30 days.

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

Metrics

CVSS 3.1

4.3/10

CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:N/A:N

EPSS Probability

0.18%

8.2th percentile

Probability of exploitation in the next 30 days. Learn more

Weakness Enumeration

CWE-203

Affected Software

Vendor	Product	Versions
Mattermost	Mattermost Server	>= 10.11.0, < 10.11.11
Mattermost	Mattermost Server	>= 11.2.0, < 11.2.3
Mattermost	Mattermost Server	>= 11.3.0, < 11.3.1

References

https://mattermost.com/security-updatesVendor Advisory

Timeline

Published: Mar 16, 2026
Last Modified: Jun 17, 2026
Status: Analyzed

Frequently Asked Questions

What is CVE-2026-21386?

How severe is CVE-2026-21386?

CVE-2026-21386 has a CVSS score of 4.3/10 (MEDIUM severity). The EPSS model estimates a 0.18% probability of exploitation in the next 30 days.

How do I fix CVE-2026-21386?

Check the vendor references and advisories linked above for patched versions and mitigation guidance. You can also run a Strix scan to test if your systems are affected.

Are you affected by CVE-2026-21386?

Run a free Strix scan to check your systems for this vulnerability.

Scan your code now

Source: NVD / NIST