CVE-2026-9859CWE-863broken-access-control

CVE-2026-9859

Medium · published August 18, 2026

CVSS v3.1
6.5
EPSS
0%
Percentile
26.3
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 enforce PermissionManageBoardRoles on the channelId field of the batch endpoint, which allows an authenticated board editor to relink any board they can edit to an arbitrary channel via a crafted PATCH request. Mattermost Advisory ID: MMSA-2026-00686

The record
Technical detail
CVSS v3.1
6.5 · MEDIUM
Vector
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:N
CVSS v4.0
Not supplied
EPSS
0.00340 · 26.3th 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 22:06Z
    Mattermost Boards plugin didn’t enforce role-based authorization on board channel link allowing board editors to expose boards to arbitrary channels
    cvelistv5