CVE-2026-21386
Mattermost fails to use consistent error responses when handling the /mute command in github.com/mattermost/mattermost-server
Description
Mattermost fails to use consistent error responses when handling the /mute command in github.com/mattermost/mattermost-server. NOTE: The source advisory for this report contains additional versions that could not be automatically mapped to standard Go module versions. (If this is causing false-positive reports from vulnerability scanners, please suggest an edit to the report.) The additional affected modules and versions are: github.com/mattermost/mattermost-server/v5 before v5.3.2-0.20260130144323-5bb5261c72fa.
How to fix CVE-2026-21386
To remediate CVE-2026-21386, upgrade the affected package to a fixed version below.
- —upgrade to 5.3.2-0.20260130144323-5bb5261c72fa or later
- —upgrade to 10.11.11+incompatible or later
- —no fix listed
- —no fix listed
- —upgrade to 8.0.0-20260130144323-5bb5261c72fa or later
- —upgrade to 8.0.0-20260130144323-5bb5261c72fa or later
Is CVE-2026-21386 being exploited?
Low — EPSS is 0.0%, meaning exploitation activity has not been observed at scale.
Affected packages (6)
- from 0, < 5.3.2-0.20260130144323-5bb5261c72fa
- >= 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
- from 0
- from 0
- from 0, < 8.0.0-20260130144323-5bb5261c72fa
- from 0, < 8.0.0-20260130144323-5bb5261c72fa
CVSS scores
| Source | Version | Severity | Vector |
|---|---|---|---|
| osv | CVSS 3.1 | MEDIUM4.3 | CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:N/A:N |