CVE-2023-2787 in Server
Summary
by MITRE • 06/16/2023
Mattermost fails to check channel membership when accessing message threads, allowing an attacker to access arbitrary posts by using the message threads API.
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Analysis
by VulDB Data Team • 06/16/2023
The vulnerability identified as CVE-2023-2787 represents a critical access control flaw within the Mattermost collaboration platform that undermines the integrity of channel-based security models. This issue affects the message threads API functionality where the system fails to properly validate user permissions before granting access to specific message threads. The flaw exists in the authentication and authorization mechanisms that should enforce channel membership restrictions, creating a path for unauthorized access to confidential communications and data. Such a vulnerability directly impacts the principle of least privilege and can lead to information disclosure across multiple channels within the platform.
The technical implementation of this vulnerability stems from insufficient input validation and access control checks within the message threads API endpoint. When users attempt to access specific message threads through the API, the system does not verify whether the requesting user has proper membership rights to the channel containing those threads. This oversight allows attackers to craft API requests with arbitrary thread identifiers and potentially access posts from channels they should not be authorized to view. The flaw operates at the application layer and can be exploited through direct API calls without requiring elevated privileges or complex attack chains. According to CWE classification, this vulnerability maps to CWE-285: Improper Authorization, which specifically addresses insufficient authorization checks in software systems.
The operational impact of CVE-2023-2787 extends beyond simple data exposure to encompass potential compromise of sensitive business communications, intellectual property, and confidential discussions. Attackers could leverage this vulnerability to access private channel conversations, employee communications, strategic planning discussions, and other sensitive content that should remain restricted to authorized participants only. The vulnerability affects organizations using Mattermost in enterprise environments where channel-based access control is fundamental to maintaining information security boundaries. Depending on the configuration and usage patterns, this flaw could enable attackers to gather intelligence about organizational structure, ongoing projects, security measures, and other potentially valuable information.
Organizations utilizing Mattermost should implement immediate mitigations including applying the vendor-provided security patches and updates as soon as they become available. Network segmentation and API rate limiting can provide additional defensive layers while waiting for official patches. Access control policies should be reviewed and strengthened to ensure that API endpoints properly validate user permissions before granting access to sensitive resources. Security monitoring should be enhanced to detect unusual API access patterns and unauthorized attempts to access message threads. From an ATT&CK framework perspective, this vulnerability aligns with techniques such as T1078 Valid Accounts and T1566 Phishing, as attackers may use compromised credentials to exploit this flaw or conduct reconnaissance activities. Organizations should also consider implementing automated vulnerability scanning and penetration testing to identify similar access control weaknesses in their deployment environments.