CVE-2026-8821

Playbooks run owner channel membership permission bypass

State: Published
Severity: 7.1 High
Published: Sep 14, 2026
Updated: Sep 14, 2026
Reserved: May 18, 2026

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

Scores

CVSS	Score	Vector	Source
3.1	7.1 High	CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:L/A:N	Mattermost

Weaknesses

CWE-862 Missing Authorization

Affected Products

Product	Versions
MattermostMattermost	11.9.0 through 11.9.0Affected 11.8.0 through 11.8.4Affected 11.7.0 through 11.7.7Affected 10.11.0 through 10.11.22Affected 11.10.0Not affected 11.9.1Not affected 11.8.5Not affected 11.7.8Not affected 10.11.23Not affected

References

MMSA-2026-00677vendor-advisory

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