Mattermost versions 11.7.x <= 11.7.6, 11.8.x <= 11.8.3 The access control policy unassign endpoint fails to re-validate that each target channel… (CVE-2026-15754)
Mattermost versions 11.7.x up to 11.7.6 and 11.8.x up to 11.8.3 contain a vulnerability in the access control policy unassign endpoint. This endpoint does not properly re-validate that each target channel still belongs to the requesting admin's team, allowing an authenticated team administrator to remove attribute-based access control (ABAC) policy assignments from channels outside their team after those channels have been moved to another team. The vulnerability has a CVSS 3.1 score of 4.2, indicating medium severity.
AI Analysis
Technical Summary
In Mattermost versions 11.7.x <= 11.7.6 and 11.8.x <= 11.8.3, the access control policy unassign API endpoint fails to re-validate channel ownership relative to the requesting admin's team. This allows an authenticated team administrator to remove ABAC policy assignments from channels that have been moved to a different team, bypassing intended access control restrictions. The issue is tracked as CVE-2026-15754 and corresponds to CWE-863 (Incorrect Authorization).
Potential Impact
An authenticated team administrator can remove ABAC policy assignments from channels outside their own team, potentially weakening access controls on those channels. There is no impact on confidentiality or availability, but integrity of access control policies can be compromised. The vulnerability requires high privileges (team admin) and user interaction (API call).
Mitigation Recommendations
Patch status is not yet confirmed — check the vendor advisory for current remediation guidance. No official fix or patch links are provided in the available data. Until a patch is available, restrict team administrator privileges carefully and monitor for unusual policy unassign API usage.
Mattermost versions 11.7.x <= 11.7.6, 11.8.x <= 11.8.3 The access control policy unassign endpoint fails to re-validate that each target channel… (CVE-2026-15754)
Description
Mattermost versions 11.7.x up to 11.7.6 and 11.8.x up to 11.8.3 contain a vulnerability in the access control policy unassign endpoint. This endpoint does not properly re-validate that each target channel still belongs to the requesting admin's team, allowing an authenticated team administrator to remove attribute-based access control (ABAC) policy assignments from channels outside their team after those channels have been moved to another team. The vulnerability has a CVSS 3.1 score of 4.2, indicating medium severity.
CVSS v3.1
Score 4.2medium
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
In Mattermost versions 11.7.x <= 11.7.6 and 11.8.x <= 11.8.3, the access control policy unassign API endpoint fails to re-validate channel ownership relative to the requesting admin's team. This allows an authenticated team administrator to remove ABAC policy assignments from channels that have been moved to a different team, bypassing intended access control restrictions. The issue is tracked as CVE-2026-15754 and corresponds to CWE-863 (Incorrect Authorization).
Potential Impact
An authenticated team administrator can remove ABAC policy assignments from channels outside their own team, potentially weakening access controls on those channels. There is no impact on confidentiality or availability, but integrity of access control policies can be compromised. The vulnerability requires high privileges (team admin) and user interaction (API call).
Mitigation Recommendations
Patch status is not yet confirmed — check the vendor advisory for current remediation guidance. No official fix or patch links are provided in the available data. Until a patch is available, restrict team administrator privileges carefully and monitor for unusual policy unassign API usage.
Technical Details
- Gcve Source
- db.gcve.eu
- Osv Id
- GHSA-mg83-f953-3vq5
- Osv Schema Version
- 1.4.0
- Aliases
- ["CVE-2026-15754"]
- Ecosystems
- []
- Database Specific Severity
- MODERATE
- Cvss Version
- 3.1
Threat ID: 6a833342bf8831d5392a3a97
Added to database: 08/17/2026, 16:13:54 UTC
Last enriched: 08/17/2026, 16:15:36 UTC
Last updated: 08/17/2026, 19:01:22 UTC
Views: 3
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