CVE-2026-9816
Medium
Elevated severity or exploit probability.
CVSS base
8.3
HIGH
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:H/A:H
EPSS — probability of exploitation (30 days)
0.3%
18.2th percentile
CISA KEV
Not listed
Weakness / dates
CWE-863
Published 2026-08-17 · modified 2026-08-19
CVSS breakdown
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:H/A:H
| Attack Vector | N | Network |
| Attack Complexity | L | Low |
| Privileges Required | L | Low |
| User Interaction | N | None |
| Scope | U | Unchanged |
| Confidentiality | L | Low |
| Integrity | H | High |
| Availability | H | High |
Timeline
- 2026-08-17 — Published (NVD)
- 2026-08-19 — Last modified (NVD)
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