CVE-2026-9859

Mattermost Boards plugin didn’t enforce role-based authorization on board channel link allowing board editors to expose boards to arbitrary channels

State: Published
Severity: 6.5 Medium
Published: Aug 17, 2026
Updated: Aug 18, 2026
Reserved: May 28, 2026

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Description

Mattermost versions 11.7.x <= 11.7.6, 10.11.x <= 10.11.21, 11.8.x <= 11.8.3 fail to enforce PermissionManageBoardRoles on the channelId field of the batch endpoint, which allows an authenticated board editor to relink any board they can edit to an arbitrary channel via a crafted PATCH request. Mattermost Advisory ID: MMSA-2026-00686

Scores

CVSS	Score	Vector	Source
3.1	6.5 Medium	CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:N	Mattermost

Weaknesses

CWE-863 Incorrect Authorization

Affected Products

Product	Versions
MattermostMattermost	11.7.0 through 11.7.6Affected 10.11.0 through 10.11.21Affected 11.8.0 through 11.8.3Affected 11.9.0Not affected 11.7.7Not affected 10.11.22Not affected 11.8.4Not affected

References

MMSA-2026-00686vendor-advisory

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