CVE-2026-9816 — Insufficient server-side validation of board member role fields permits privilege escalation

CVE-2026-9816

Insufficient server-side validation of board member role fields permits privilege escalation PUBLISHED

Description (CNA)

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

Affected (CNA)

Vendor / product	Versions
Mattermost / Mattermost	affected 11.7.0 through 11.7.6; affected 10.11.0 through 10.11.21; affected 11.8.0 through 11.8.3; unaffected 11.9.0; unaffected 11.7.7; unaffected 10.11.22; unaffected 11.8.4

CWE

CWE-863

References

https://mattermost.com/security-updates

ADP enrichment

CISA-ADP

No English description supplied.

No references supplied.