CVE-2026-9859 PUBLISHED

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

Assigner: Mattermost
Reserved: 28.05.2026 Published: 17.08.2026 Updated: 17.08.2026

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

Metrics

CVSS 3.1

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

Attack Vector	Network	Scope	Unchanged
Attack Complexity	Low	Confidentiality Impact	High
Privileges Required	Low	Integrity Impact	None
User Interaction	None	Availability Impact	None

CVSS 3.1

Product Status

Vendor	Mattermost
Product	Mattermost
Versions	Default: unaffected affected from 11.7.0 to 11.7.6 (incl.) affected from 10.11.0 to 10.11.21 (incl.) affected from 11.8.0 to 11.8.3 (incl.) Version 11.9.0 is unaffected Version 11.7.7 is unaffected Version 10.11.22 is unaffected Version 11.8.4 is unaffected

Solutions

Update Mattermost to versions 11.9.0, 11.7.7, 10.11.22, 11.8.4 or higher.

Credits

kauasilvab14fb3 finder

References

MMSA-2026-00686

Problem Types

CWE-863: Incorrect Authorization CWE