Access Control Bypass in Mattermost 11.7-11.8 via unassign API
CVE-2026-15754 Published on August 17, 2026
Missing per-channel team-scope check in ABAC access control policy unassign allows cross-team policy removal
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 still belongs to the requesting admin's team, which allows an authenticated team administrator to remove ABAC (attribute-based access control) policy assignments from channels outside their team via the policy unassign API after a channel has been moved to another team.. Mattermost Advisory ID: MMSA-2026-00718
Vulnerability Analysis
CVE-2026-15754 is exploitable with network access, requires user interaction and user privileges. This vulnerability is consided to have a high level of attack complexity. The potential impact of an exploit of this vulnerability is considered to have no impact on confidentiality, a high impact on integrity, and no impact on availability.
Weakness Type
What is an AuthZ Vulnerability?
The software performs an authorization check when an actor attempts to access a resource or perform an action, but it does not correctly perform the check. This allows attackers to bypass intended access restrictions.
CVE-2026-15754 has been classified to as an AuthZ vulnerability or weakness.
Products Associated with CVE-2026-15754
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Affected Versions
Mattermost:- Version 11.7.0, <= 11.7.6 is affected.
- Version 11.8.0, <= 11.8.3 is affected.
- Version 11.9.0 is unaffected.
- Version 11.7.7 is unaffected.
- Version 11.8.4 is unaffected.