Medium severity · published Mar 16, 2026
CVE-2026-21386
Private channel enumeration via /mute slash command
4.3
CVSS
0.2%
EPSS
No
On KEV
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 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 interaction
None
Confidentiality
Low
Integrity
None
Availability
None
Scope
Unchanged
Exploitation
Is it being used?
Exploit prediction (EPSS)0.2% · higher than 8% of CVEs
Exploited in the wildNo evidence yet
CISA KEVNot listed
Ransomware campaign useNot known
Affected products
Which versions
MA
Mattermost · Mattermost
11.3.0 through 11.3.0; 11.2.0 through 11.2.2; 10.11.0 through 10.11.10 · source: vendor
MS
Mattermost Server · Mattermost
10.11.0 before 10.11.11; 11.2.0 before 11.2.3; 11.3.0 before 11.3.1 · source: NVD
References
NVD
https://nvd.nist.gov/vuln/detail/CVE-2026-21386
CVE.org
https://www.cve.org/CVERecord?id=CVE-2026-21386
Vendor Advisory
https://mattermost.com/security-updates
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