Description
Mattermost versions 11.7.x <= 11.7.6, 10.11.x <= 10.11.21, 11.8.x <= 11.8.3 fails to reconcile SchemeAdmin flags with a user's current role which allows a user demoted to System Guest to retain Board Admin privileges and perform admin-only operations via the Boards REST API or UI.. Mattermost Advisory ID: MMSA-2026-00691
Published: 2026-08-17
Score: 6.3 Medium
EPSS: n/a
KEV: No
Impact: n/a
Action: n/a
AI Analysis

Impact

The Boards plugin for Mattermost fails to reconcile SchemeAdmin flags when a user is demoted to System Guest, allowing the user to retain Board Admin privileges. This flaw permits the user to execute admin‑only operations through the Boards REST API or user interface, enabling unauthorized privilege escalation within the Mattermost platform.

Affected Systems

Affected versions are Mattermost 10.11.x up to 10.11.21, 11.7.x up to 11.7.6, and 11.8.x up to 11.8.3. The issue arises in the Boards plugin component of Mattermost and involves the core platform’s role‑management logic.

Risk and Exploitability

With a CVSS score of 6.3 the vulnerability is of moderate severity. The EPSS score is not available, and it is not listed in the CISA KEV catalog. Based on the description, the likely attack vector is via the Boards REST API or UI, allowing a demoted user to perform administrative actions remotely if the Mattermost instance is reachable over the network.

Generated by OpenCVE AI on August 17, 2026 at 15:37 UTC.

Remediation

Vendor Solution

Update Mattermost to versions 11.9.0, 11.7.7, 10.11.22, 11.8.4 or higher.

OpenCVE Recommended Actions

  • Update Mattermost to version 11.9.0, 11.7.7, 10.11.22, 11.8.4, or later.
  • Remove Board Admin permissions from all users assigned the System Guest role until the update is applied.
  • Enable auditing of board administration actions to detect and investigate any unauthorized activity post‑remediation.

Generated by OpenCVE AI on August 17, 2026 at 15:37 UTC.

Tracking

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Advisories

No advisories yet.

References
Link Providers
https://mattermost.com/security-updates cve-icon cve-icon
History

Mon, 17 Aug 2026 15:45:00 +0000

Type Values Removed Values Added
First Time appeared Mattermost
Mattermost mattermost
Vendors & Products Mattermost
Mattermost mattermost

Mon, 17 Aug 2026 14:45:00 +0000

Type Values Removed Values Added
Description Mattermost versions 11.7.x <= 11.7.6, 10.11.x <= 10.11.21, 11.8.x <= 11.8.3 fails to reconcile SchemeAdmin flags with a user's current role which allows a user demoted to System Guest to retain Board Admin privileges and perform admin-only operations via the Boards REST API or UI.. Mattermost Advisory ID: MMSA-2026-00691
Title Boards plugin retains Board Admin rights for users demoted to System Guest
Weaknesses CWE-863
References
Metrics cvssV3_1

{'score': 6.3, 'vector': 'CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:L/A:L'}

Subscriptions

Mattermost Mattermost
cve-icon MITRE

Status: PUBLISHED

Assigner: Mattermost

Published:

Updated: 2026-08-17T15:25:25.134Z

Reserved: 2026-06-01T10:10:10.052Z

Link: CVE-2026-10527

cve-icon Vulnrichment

No data.

cve-icon NVD

Status : Received

Published: 2026-08-17T15:16:53.087

Modified: 2026-08-17T15:16:53.087

Link: CVE-2026-10527

cve-icon Redhat

No data.

cve-icon OpenCVE Enrichment

Updated: 2026-08-17T15:30:06Z

Weaknesses