CVE-2026-8821
High
Description
Mattermost versions 11.9.x <= 11.9.0, 11.8.x <= 11.8.4, 11.7.x <= 11.7.7, 10.11.x <= 10.11.22 fail to validate channel member-management permission during playbook run creation, allowing an authenticated channel member to add an arbitrary user to a restricted channel via the run owner field.. Mattermost Advisory ID: MMSA-2026-00677
SeverityHigh
CVSS7.1
Exploit probability—
Product
Mattermost Server
PublishedSep 14, 2026
First seenSep 14, 2026
Weakness typeCWE-862Missing authorization
How to fix
Update
- mattermost mattermost_server10.11.23, 11.7.8, 11.8.5, 11.9.1 or later
Vendor advisories
Affected products
| Product | Affected versions | Fixed in |
|---|---|---|
| mattermost mattermost_server | 10.11.0 ≤ v < 10.11.23, 11.7.0 ≤ v < 11.7.8, 11.8.0 ≤ v < 11.8.5, 11.9.0 ≤ v < 11.9.1 | 10.11.23, 11.7.8, 11.8.5, 11.9.1 |
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