CVE-2024-24776 in Mattermost
Summary
by MITRE • 02/09/2024
Mattermost fails to check the required permissions in the POST /api/v4/channels/stats/member_count API resulting in channel member counts being leaked to a user without permissions.
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Analysis
by VulDB Data Team • 03/03/2024
The vulnerability identified as CVE-2024-24776 represents a critical access control flaw within the Mattermost collaboration platform that undermines the integrity of channel membership data. This issue specifically affects the POST /api/v4/channels/stats/member_count API endpoint where the system fails to validate whether authenticated users possess the necessary permissions to access channel member count statistics. The flaw exists in the platform's authorization mechanism, where proper privilege checks are not enforced when processing requests to retrieve channel membership information through this particular API endpoint.
The technical implementation of this vulnerability stems from insufficient input validation and authorization logic within the Mattermost server-side API handling. When a user submits a request to the member_count endpoint, the system should verify that the requesting user has appropriate access rights to the target channel before returning member count data. However, the current implementation bypasses this critical permission check, allowing any authenticated user to obtain channel membership statistics regardless of their role or access level within the channel. This misconfiguration creates a clear path for information disclosure where unauthorized users can gather sensitive data about channel membership, potentially revealing the size and composition of private or restricted communication groups.
The operational impact of this vulnerability extends beyond simple information leakage to encompass significant security implications for organizations relying on Mattermost for secure communications. Attackers could exploit this flaw to enumerate channel memberships across different teams and workspaces, potentially identifying sensitive channels, mapping communication patterns, and discovering high-value targets for further social engineering or targeted attacks. The vulnerability particularly affects organizations with strict data governance policies where channel membership information should remain confidential to maintain operational security and protect against insider threats. This flaw directly violates the principle of least privilege and could enable adversaries to gain intelligence about organizational structures, team compositions, and communication dynamics that would otherwise remain private.
From a cybersecurity framework perspective, this vulnerability aligns with CWE-284 (Improper Access Control) and represents a clear violation of the access control principles outlined in the NIST Cybersecurity Framework. The issue also maps to ATT&CK technique T1087.001 (Account Discovery: Local Account) and T1566 (Phishing) as attackers could use the leaked information to craft more convincing social engineering campaigns. Organizations implementing Mattermost should consider this vulnerability as part of their broader security posture assessment, particularly in environments where information disclosure could lead to compliance violations or operational compromise. The flaw demonstrates a critical gap in the platform's security architecture where API endpoints are not adequately protected against unauthorized access attempts.
Mitigation strategies for this vulnerability should include immediate implementation of proper permission checks within the affected API endpoint, ensuring that all requests are validated against the requesting user's access rights before returning channel member count data. Organizations should also implement comprehensive API access logging to detect unauthorized access attempts and establish monitoring procedures to identify potential exploitation of this vulnerability. The Mattermost platform should be updated to the latest version where this issue has been addressed through proper authorization enforcement. Additionally, security teams should conduct thorough audits of all API endpoints to identify similar permission validation gaps and implement consistent access control measures across the entire platform. Network segmentation and API gateway controls can provide additional layers of protection, while regular security assessments should include testing for unauthorized access to sensitive data through API interfaces.