CVE-2023-6547 in Mattermost
Summary
by MITRE • 12/12/2023
Mattermost fails to validate team membership when a user attempts to access a playbook, allowing a user with permissions to a playbook but no permissions to the team the playbook is on to access and modify the playbook. This can happen if the user was once a member of the team, got permissions to the playbook and was then removed from the team.
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Analysis
by VulDB Data Team • 01/02/2024
This vulnerability in Mattermost represents a critical access control flaw that undermines the platform's security model through improper validation of team membership during playbook access operations. The issue stems from a failure in the authorization logic where the system allows users to access playbooks based solely on their playbook-specific permissions without verifying their current team membership status. This represents a classic privilege escalation vulnerability where former team members retain access to resources they should no longer be able to modify, creating a persistent security gap that can be exploited by malicious actors or compromised accounts.
The technical implementation flaw manifests when a user who was previously a member of a team but has since been removed from that team retains playbook permissions and can still access and modify playbook content. This occurs because the system does not enforce real-time team membership validation during playbook access requests, allowing the user to bypass normal team-based access controls. The vulnerability exists in the playbook access control mechanism where the authorization check only validates playbook-specific permissions rather than cross-referencing current team membership status, creating an authorization bypass that can be exploited by users with stale permissions.
The operational impact of this vulnerability extends beyond simple unauthorized access to include potential data integrity compromise and information disclosure risks. An attacker with playbook access but no team membership could modify playbook content, potentially introducing malicious workflows or altering critical operational procedures that other team members rely upon. This could lead to significant operational disruption, especially in environments where playbooks contain sensitive operational procedures or compliance-related processes. The vulnerability also creates a persistent backdoor for former team members who may have legitimate access to playbook content but should not be able to modify it without proper team membership, potentially leading to unauthorized changes to operational workflows.
From a cybersecurity perspective, this vulnerability aligns with CWE-285 (Improper Authorization) and represents a failure in the principle of least privilege enforcement. The issue demonstrates a lack of proper access control validation that could be exploited through various attack vectors including social engineering to gain initial access, or by compromising accounts of former team members. Organizations using Mattermost should consider this vulnerability in their threat modeling and incident response planning, particularly in environments where playbooks contain sensitive operational data or where strict access controls are required for compliance purposes. The vulnerability also relates to ATT&CK technique T1078 (Valid Accounts) and T1531 (Account Access Removal) as it enables persistent access through compromised or former accounts while potentially masking the actual unauthorized access through legitimate playbook permissions.
Mitigation strategies should focus on implementing immediate patching of the Mattermost platform to address the authorization validation flaw, combined with proactive monitoring of playbook access patterns to detect unauthorized modifications. Organizations should also implement regular permission audits to ensure that playbook permissions are properly synchronized with current team membership status, and consider implementing additional access controls that enforce real-time validation of team membership during playbook access operations. The vulnerability highlights the importance of maintaining proper access control lifecycle management and demonstrates why continuous monitoring of access patterns and permission changes is essential for maintaining secure platform operations.