cve.bz

CVE-2026-21386

4.3 mediumEPSS 0.2%

Medium (4.3) in mattermost mattermost server. EPSS 0.2% chance of exploitation in the next 30 days. Fixed in github.com/mattermost/mattermost/server/v8 8.0.0-20260130144323-5bb5261c72fa.

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

Severity

CVSS 3.1

4.3 medium
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:N/A:N
EPSS
0.2% chance of exploitation in the next 30 days; higher than 8% of CVEs (scores of 2026-10-31)
CWE
CWE-203
Published
Modified
Record from
the NVD, synced

Affected

Packages (OSV)

AdvisoryEcosystemPackageAffectedFixed in
GHSA-5mr9-crcg-8wh2Gogithub.com/mattermost/mattermost/server/v8<8.0.0-20260130144323-5bb5261c72fa8.0.0-20260130144323-5bb5261c72fa
GHSA-5mr9-crcg-8wh2Gogithub.com/mattermost/mattermost-server<5.3.2-0.20260130144323-5bb5261c72fa5.3.2-0.20260130144323-5bb5261c72fa
GHSA-5mr9-crcg-8wh2Gogithub.com/mattermost/mattermost-server>=10.11.0-rc1 <10.11.1110.11.11
GHSA-5mr9-crcg-8wh2Gogithub.com/mattermost/mattermost-server>=11.2.0-rc1 <11.2.311.2.3
GHSA-5mr9-crcg-8wh2Gogithub.com/mattermost/mattermost-server>=11.3.0-rc1 <11.3.111.3.1
GO-2026-4744Gogithub.com/mattermost/mattermost-server>=10.11.0-rc1+incompatible <10.11.11+incompatible
>=11.2.0-rc1+incompatible <11.2.3+incompatible
>=11.3.0-rc1+incompatible <11.3.1+incompatible		10.11.11+incompatible, 11.2.3+incompatible, 11.3.1+incompatible
GO-2026-4744Gogithub.com/mattermost/mattermost-server/v5all versionsno fix published
GO-2026-4744Gogithub.com/mattermost/mattermost-server/v6all versionsno fix published
GO-2026-4744Gogithub.com/mattermost/mattermost/server/v8<8.0.0-20260130144323-5bb5261c72fa8.0.0-20260130144323-5bb5261c72fa

References

Check your stackJSON