CVE-2019-20846 in Mattermost Server
Summary
by MITRE
An issue was discovered in Mattermost Server before 5.18.0. It has weak permissions for server-local file storage.
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Analysis
by VulDB Data Team • 10/25/2020
The vulnerability identified as CVE-2019-20846 represents a critical access control weakness within the Mattermost Server platform that affects versions prior to 5.18.0. This issue stems from inadequate permission controls governing server-local file storage mechanisms, creating potential security risks for organizations relying on the platform for collaborative communication. The flaw allows unauthorized access to files stored locally on the server, potentially exposing sensitive data and compromising the integrity of the communication environment. Organizations utilizing Mattermost for enterprise communication may face significant security implications due to this vulnerability, particularly in environments where strict data governance and access controls are required.
The technical implementation of this vulnerability manifests through insufficient file system permission checks within the Mattermost server architecture. When files are stored locally on the server, the platform fails to properly enforce access controls that would normally restrict file visibility and modification capabilities to authorized users only. This weakness creates an attack surface where malicious actors or compromised user accounts could potentially access, modify, or exfiltrate files stored within the server's local storage. The vulnerability specifically affects the server-local file storage functionality, which is commonly used for document sharing, attachment handling, and other file-related operations within the Mattermost ecosystem. According to CWE classification, this represents a weakness in permissions and access control mechanisms, specifically falling under CWE-284 which addresses improper access control.
The operational impact of CVE-2019-20846 extends beyond simple data exposure, potentially enabling broader system compromise and data integrity violations. Organizations may experience unauthorized access to sensitive documents, user communications, and system files that should remain protected. The vulnerability's presence in server-local storage creates opportunities for attackers to escalate privileges or conduct data exfiltration campaigns. Additionally, the weakness may facilitate persistence mechanisms within the compromised environment, allowing attackers to maintain access over extended periods. From an attacker's perspective, this vulnerability aligns with techniques described in the MITRE ATT&CK framework under the privilege escalation and defense evasion domains, where attackers seek to gain unauthorized access to system resources and maintain covert operations.
Organizations should prioritize immediate remediation by upgrading to Mattermost Server version 5.18.0 or later, which contains the necessary patches addressing the weak permissions issue. Security teams should conduct comprehensive audits of file storage permissions and access controls within their Mattermost environments to identify any potential exploitation that may have occurred. Network segmentation and monitoring controls should be enhanced to detect unauthorized access attempts to file storage areas. The vulnerability serves as a reminder of the importance of proper access control implementation in collaborative platforms, particularly those handling sensitive organizational data. Regular security assessments and vulnerability management processes should include evaluation of file system permissions and access controls to prevent similar weaknesses from emerging in other components of the platform infrastructure.