CVE-2026-21386
low-risk
Published 2026-03-16
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
Do I need to act?
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0.03% chance of exploitation
EPSS score — low exploit probability
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Not on CISA KEV list
No confirmed active exploitation reported to CISA
?
Patch status unknown
Check vendor advisories for fix availability and mitigation guidance
4
CVSS 4.3/10
Medium
NETWORK
/ LOW complexity
Affected Products (1)
Affected Vendors
References (1)
Vendor Advisory
https://mattermost.com/security-updates
23
/ 100
low-risk
Severity
18/34 · Moderate
Exploitability
0/34 · Minimal
Exposure
5/34 · Minimal