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… (CVE-2026-9859)
Mattermost versions 11.7.x up to 11.7.6, 10.11.x up to 10.11.21, and 11.8.x up to 11.8.3 contain a vulnerability where the PermissionManageBoardRoles permission is not enforced on the channelId field of the batch endpoint. This flaw allows an authenticated board editor to relink any board they can edit to an arbitrary channel by sending a crafted PATCH request. The vulnerability has a moderate severity with a CVSS score of 6.5.
AI Analysis
Technical Summary
Mattermost versions 11.7.x <= 11.7.6, 10.11.x <= 10.11.21, and 11.8.x <= 11.8.3 fail to enforce the PermissionManageBoardRoles permission on the channelId field of the batch endpoint. This permission enforcement failure allows an authenticated user with board editor privileges to relink any board they can edit to an arbitrary channel by crafting a PATCH request targeting the channelId field. The issue is tracked as CVE-2026-9859 and corresponds to CWE-863 (Improper Authorization). No known exploits in the wild have been reported. No patch or remediation information is provided in the available data.
Potential Impact
An authenticated board editor can relink boards to arbitrary channels without proper authorization checks, potentially leading to unauthorized changes in board-channel associations. This could affect board organization and access control within Mattermost environments. The vulnerability does not impact confidentiality, integrity of data beyond the channel linkage, or availability.
Mitigation Recommendations
Patch status is not yet confirmed — check the vendor advisory (Mattermost Advisory ID: MMSA-2026-00686) for current remediation guidance. Until an official fix is available, restrict board editor permissions to trusted users only and monitor for unusual board relinking activities.
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… (CVE-2026-9859)
Description
Mattermost versions 11.7.x up to 11.7.6, 10.11.x up to 10.11.21, and 11.8.x up to 11.8.3 contain a vulnerability where the PermissionManageBoardRoles permission is not enforced on the channelId field of the batch endpoint. This flaw allows an authenticated board editor to relink any board they can edit to an arbitrary channel by sending a crafted PATCH request. The vulnerability has a moderate severity with a CVSS score of 6.5.
CVSS v3.1
Score 6.5medium
Affected software
pkg:github/mattermost/mattermost-serverRun on your own infrastructure? Check whether these packages are installed with threat-finder — our free open-source scanner.
Weaknesses
AI-Powered Analysis
Machine-generated threat intelligence
Technical Analysis
Mattermost versions 11.7.x <= 11.7.6, 10.11.x <= 10.11.21, and 11.8.x <= 11.8.3 fail to enforce the PermissionManageBoardRoles permission on the channelId field of the batch endpoint. This permission enforcement failure allows an authenticated user with board editor privileges to relink any board they can edit to an arbitrary channel by crafting a PATCH request targeting the channelId field. The issue is tracked as CVE-2026-9859 and corresponds to CWE-863 (Improper Authorization). No known exploits in the wild have been reported. No patch or remediation information is provided in the available data.
Potential Impact
An authenticated board editor can relink boards to arbitrary channels without proper authorization checks, potentially leading to unauthorized changes in board-channel associations. This could affect board organization and access control within Mattermost environments. The vulnerability does not impact confidentiality, integrity of data beyond the channel linkage, or availability.
Mitigation Recommendations
Patch status is not yet confirmed — check the vendor advisory (Mattermost Advisory ID: MMSA-2026-00686) for current remediation guidance. Until an official fix is available, restrict board editor permissions to trusted users only and monitor for unusual board relinking activities.
Technical Details
- Gcve Source
- db.gcve.eu
- Osv Id
- GHSA-27x7-qjjm-4f83
- Osv Schema Version
- 1.4.0
- Aliases
- ["CVE-2026-9859"]
- Ecosystems
- []
- Database Specific Severity
- MODERATE
- Cvss Version
- 3.1
Threat ID: 6a83aa68bf8831d539e30f3b
Added to database: 08/18/2026, 00:42:16 UTC
Last enriched: 08/18/2026, 01:13:26 UTC
Last updated: 08/18/2026, 02:01:14 UTC
Views: 3
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