Description
Mattermost versions 11.7.x <= 11.7.6, 10.11.x <= 10.11.21, 11.8.x <= 11.8.3 fail to validate BoardMember.Scheme* fields server-side on insert and archive-import paths which allows a board editor or non-guest team member to grant board admin to arbitrary users via POST /api/v2/boards/{boardID}/members and POST /api/v2/teams/{teamID}/archive/import.. Mattermost Advisory ID: MMSA-2026-00685
Published: 2026-08-17
Score: 8.3 High
EPSS: n/a
KEV: No
Impact: n/a
Action: n/a
AI Analysis

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Remediation

Vendor Solution

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

Tracking

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Advisories

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References
Link Providers
https://mattermost.com/security-updates cve-icon cve-icon
History

Mon, 17 Aug 2026 22:15:00 +0000

Type Values Removed Values Added
Description Mattermost versions 11.7.x <= 11.7.6, 10.11.x <= 10.11.21, 11.8.x <= 11.8.3 fail to validate BoardMember.Scheme* fields server-side on insert and archive-import paths which allows a board editor or non-guest team member to grant board admin to arbitrary users via POST /api/v2/boards/{boardID}/members and POST /api/v2/teams/{teamID}/archive/import.. Mattermost Advisory ID: MMSA-2026-00685
Title Insufficient server-side validation of board member role fields permits privilege escalation
Weaknesses CWE-863
References
Metrics cvssV3_1

{'score': 8.3, 'vector': 'CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:H/A:H'}

Subscriptions

No data.

cve-icon MITRE

Status: PUBLISHED

Assigner: Mattermost

Published:

Updated: 2026-08-17T22:05:24.910Z

Reserved: 2026-05-28T09:54:00.723Z

Link: CVE-2026-9816

cve-icon Vulnrichment

No data.

cve-icon NVD

Status : Received

Published: 2026-08-17T22:17:27.217

Modified: 2026-08-17T22:17:27.217

Link: CVE-2026-9816

cve-icon Redhat

No data.

cve-icon OpenCVE Enrichment

No data.

Weaknesses