CVE-2026-9816CWE-863broken-access-control

CVE-2026-9816

High · published August 18, 2026

CVSS v3.1
8.3
EPSS
0%
Percentile
27.4
In the wild
Unconfirmed
What it is

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

The record
Technical detail
CVSS v3.1
8.3 · HIGH
Vector
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:H/A:H
CVSS v4.0
Not supplied
EPSS
0.00350 · 27.4th percentile
Weakness
CWE-863 · Incorrect Authorization
Published
2026-08-18T02:17Z
Affected products (3)
ProductVersionsFixed in
mattermost/mattermost_server≥ 10.11.0, < 10.11.2210.11.22
mattermost/mattermost_server≥ 11.7.0, < 11.7.711.7.7
mattermost/mattermost_server≥ 11.8.0, < 11.8.411.8.4
References (1)
https://mattermost.com/security-updates · [email protected]
EPSS history
Timeline
  • 17 AUG 22:05Z
    Insufficient server-side validation of board member role fields permits privilege escalation
    cvelistv5