CVE-2026-21386 | BDVDB-2026-320782 Detail

MattermostMattermost

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

Impact#

Per CVSS v3.1: confidentiality impact low, integrity impact none, availability impact none. Attack vector: network.

Weaknesses#

CWE-203 Observable Discrepancy

References#

https://mattermost.com/security-updates

Exploit#

No public exploit known

History#

Version 12026-03-16Record published in the CVE List.

Published

Published: 2026-03-16
Last modified: 2026-03-16

Vendor information

Vendor: Mattermost
Product: Mattermost

All Mattermost vulnerabilities

Score

4.3 Medium

EPSS

less than 1%, Very Low

Estimated chance of exploitation in the next 30 days. EPSS percentile: 8.9.

KEV

Not listed in the CISA Known Exploited Vulnerabilities catalog.

Impact

Not classified

Action

No specific action is recorded in the source data. Check the references for vendor guidance.

Affected Systems

Vulnerable
>= 11.3.0 and <= 11.3.0
Fixed
Not stated
Vulnerable
>= 11.2.0 and <= 11.2.2
Fixed
Not stated
Vulnerable
>= 10.11.0 and <= 10.11.10
Fixed
Not stated
Vulnerable
Not stated
Fixed
11.4.0
Vulnerable
Not stated
Fixed
11.3.1
Vulnerable
Not stated
Fixed
11.2.3
Vulnerable
Not stated
Fixed
10.11.11

Scoring System

CVSS v4.0

Not available

CVSS v3.1

4.3 Medium

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

Metric breakdown
Attack Vector	Network
Attack Complexity	Low
Privileges Required	Low
User Interaction	None
Scope	Unchanged
Confidentiality	Low
Integrity	None
Availability	None

CVSS v3.0

Not available

CVSS v2

Not available

Source: CVE List v5 (record); CISA KEV (kev, action); FIRST EPSS (epss).