CVE-2026-21386

EUVD-2026-12437
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
ProviderTypeBase ScoreAtk. VectorAtk. ComplexityPriv. RequiredVector
MattermostCNA
4.3 MEDIUM
NETWORK
LOW
LOW
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:N/A:N
Base Score
CVSS 3.x
EPSS Score
Percentile: 13%
Affected Products (NVD)
VendorProductVersion
mattermostmattermost_server
10.11.0 ≤
𝑥
< 10.11.11
mattermostmattermost_server
11.2.0 ≤
𝑥
< 11.2.3
mattermostmattermost_server
11.3.0 ≤
𝑥
< 11.3.1
𝑥
= Vulnerable software versions
Early Detection
Affected products identified ahead of NVD analysis through intelligence sources.
VendorProductVersionSource
mattermostmattermost
𝑥
≤ 11.3.0
CNA
mattermostmattermost
11.2.0 ≤
𝑥
≤ 11.2.2
CNA
mattermostmattermost
10.11.0 ≤
𝑥
≤ 10.11.10
CNA
Common Weakness Enumeration
References
https://mattermost.com/security-updates