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CVE-2026-9859 Details

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

Metrics

CVSS 3.x Severity and Vector Strings:

CNA: [email protected]CVSS-B:6.5 MEDIUMVector:CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:N

References to Advisories, Solutions, and Tools

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URL	Source(s)	Tag(s)
https://mattermost.com/security-updates	[email protected]	Vendor Advisory

Weakness Enumeration

CWE-ID	CWE Name	Source
CWE-863	Incorrect Authorization	[email protected]

Affected Products

Product	Versions
mattermost mattermost server	>= 10.11.0, < 10.11.22 >= 11.7.0, < 11.7.7 >= 11.8.0, < 11.8.4
CPE cpe:2.3:a:mattermost:mattermost_server:::::::: Remediation No remediation found in references.

Change History

3 change records found show changes

Date	Action	Recorded By
Aug 19, 2026	Initial Analysis	[email protected]
Aug 18, 2026	CVE Modified	CISA-ADP
Aug 17, 2026	New CVE Received	[email protected]