MEDIUM
CVE-2026-21386
CWE-203Published: March 16, 2026· Updated: Mar 18, 2026
4.3
CVSS v3.1
EPSS:0.03%probability of exploitation in 30 daysPercentile:7.8th
Official 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
Technical Analysis
CVE-2026-21386 can be exploited remotely over the network without requiring physical or adjacent access, significantly expanding the attack surface for threat actors.
Exploitation requires low privileges, which limits the exposure to scenarios where an attacker has already gained initial access.
CVSS v3.1 Vector Breakdown
Exploitability
Attack VectorNetwork
Attack ComplexityLow
Privileges Req.Low
User InteractionNone
ScopeUnchanged
Impact
ConfidentialityLow
IntegrityNone
AvailabilityNone
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:N/A:N
Affected Vendors & Products
mattermost1 product
mattermost server
Source: NVD CPE · 1 total CPE entries
Exploit & PoC Resources
NO KNOWN EXPLOITNo public exploit confirmed at this time
Exploit-DB
Offensive Security exploit database
GitHub PoC Search
Community PoC repositories
Rapid7 / Metasploit
Metasploit module search
PacketStorm
Security advisories & exploits
NVD Detail
Official NIST entry
MITRE CVE
CVE Program entry
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Official Patches & Advisories
All References (1)
→
https://mattermost.com/security-updatesVendor Advisory
Quick Facts
CVE IDCVE-2026-21386
CVSS Score4.3 / 10
SeverityMEDIUM
WeaknessCWE-203
CISA KEVNo
EPSS (30d)0.03%
Affected1 vendor
PublishedMar 16, 2026
Related CVEs (CWE-203)
Recommended Actions
- →Apply vendor patches immediately
- →Monitor CVE-2026-21386 in threat intel feeds
- →Review IDS/IPS signatures for exploitation attempts
Data sourced from NVD (NIST), CISA KEV, and EPSS (FIRST). Analysis generated by CTIWATCH.COM. CVE data is provided under the NVD usage policy.