CVE-2026-9816

HighCVSS 8.3

Published: 17/08/2026(UTC)Updated: 19/08/2026(UTC)Translated: 18/08/2026(UTC)NVD NIST

Exploitation Probability (EPSS)

Low risk

0.25%

16th percentile - higher than 16% of all known CVEs

Summary

Mattermost versions 11.7.x <= 11.7.6, 10.11.x <= 10.11.21, and 11.8.x <= 11.8.3 fail to validate BoardMember.Scheme* fields server-side on insert and archive-import paths, allowing a board editor or non-guest team member to grant board admin to arbitrary users.

Risk Assessment

A user with limited privileges can escalate to board admin, potentially leading to unauthorized access and data integrity issues.

Recommendation

Update Mattermost to a patched version and review user permissions.

Original NVD description (English source)

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