CVE-2025-4128 in Mattermost
Summary
by MITRE • 06/11/2025
Mattermost versions 10.5.x <= 10.5.4, 9.11.x <= 9.11.13 fail to properly restrict API access to team information, allowing guest users to bypass permissions and view information about public teams they are not members of via a direct API call to /api/v4/teams/{team_id}.
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Analysis
by VulDB Data Team • 06/11/2025
This vulnerability affects Mattermost server implementations across specific version ranges, creating a critical access control flaw that undermines the platform's permission model. The issue stems from insufficient validation of user roles when processing API requests for team information, specifically when accessing the /api/v4/teams/{team_id} endpoint. Guest users who should only have limited access to public teams can exploit this weakness to directly query team data without proper authorization checks, effectively bypassing the intended permission boundaries that distinguish between member and non-member access levels.
The technical implementation flaw resides in the API access control logic that fails to properly verify whether a guest user has legitimate authorization to view specific team information. This represents a clear violation of the principle of least privilege and demonstrates a failure in the authorization mechanism that should enforce role-based access controls. The vulnerability operates at the application layer and specifically targets the team information retrieval functionality, where the system should validate user credentials and membership status before returning sensitive team metadata. This weakness creates a path for unauthorized information disclosure that directly impacts the confidentiality of team data within the Mattermost environment.
The operational impact of this vulnerability extends beyond simple information disclosure, as it allows malicious actors to gather intelligence about team structures, membership patterns, and organizational layouts. Guest users can exploit this flaw to enumerate public teams they are not officially part of, potentially enabling social engineering attacks, reconnaissance for targeted phishing campaigns, or analysis of organizational security posture. The vulnerability particularly affects environments where guest users are granted limited access but should not be able to view information about teams they do not belong to, creating a significant risk for organizations that rely on Mattermost for secure communication channels. This flaw can be exploited through direct API calls without requiring additional authentication credentials beyond those already available to guest users.
Organizations should implement immediate mitigations including upgrading to patched versions of Mattermost that address this access control vulnerability. The recommended approach involves applying the vendor-provided security patches that correct the API permission validation logic and ensure proper role-based access controls are enforced. Additionally, organizations should consider implementing network-level restrictions that limit direct API access to trusted internal systems and establish monitoring for unusual API access patterns. The vulnerability aligns with CWE-285, which addresses improper authorization in software applications, and could be categorized under ATT&CK technique T1566 for credential harvesting and T1083 for file and directory discovery. Organizations should also review their user role assignments and ensure that guest user permissions are properly restricted to prevent similar access control bypass scenarios.