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Vulnerability record · CVE-2026-8821 · published 14 September 2026

CVE-2026-8821: Missing authorization vulnerability

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

7.1 CVSS 3.1 High EPSS 0.29% · top 80.7% CWE-862 · Missing authorization Awaiting Analysis
7.1CVSS 3.1 base score
0.29%EPSS exploitation probability, 30 days
NoNot in CISA KEV
0Affected product versions listed by NVD
1References
16 Sep 2026Last modified by NVD

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

CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:L/A:N

References

LinkTags
https://mattermost.com/security-updates

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Source: NIST National Vulnerability Database (record CVE-2026-8821), CISA KEV, FIRST EPSS (scores of 2026-09-26). This page is refreshed as NVD updates the record.