CVE-2019-20844 in Mattermost Server
Summary
by MITRE
An issue was discovered in Mattermost Server before 5.18.0, 5.17.2, 5.16.4, 5.15.4, and 5.9.7. An attacker can spoof a direct-message channel by changing the type of a channel.
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Analysis
by VulDB Data Team • 10/25/2020
The vulnerability identified as CVE-2019-20844 represents a critical security flaw in Mattermost Server versions prior to 5.18.0, 5.17.2, 5.16.4, 5.15.4, and 5.9.7. This issue stems from insufficient validation of channel type parameters during direct message channel creation and modification processes. The flaw allows malicious actors to manipulate channel metadata to transform regular channels into direct message channels, effectively bypassing intended access controls and authentication mechanisms. The vulnerability is categorized under CWE-284 Access Control Bypass, which specifically addresses insufficient access control mechanisms that permit unauthorized users to access resources or perform actions they should not be permitted to execute.
The technical implementation of this vulnerability exploits a weakness in the server-side channel type validation logic. When an attacker modifies channel attributes through API calls or client-side manipulation, the system fails to properly verify that the channel type remains consistent with its intended purpose. Direct message channels in Mattermost are designed to be private communications between specific users, but the flaw allows an attacker to alter channel properties to make them appear as direct messages when they are actually public or group channels. This manipulation can occur through various interfaces including the REST API, WebSocket connections, or even through crafted client requests that exploit the lack of proper input sanitization and validation.
The operational impact of this vulnerability is significant and multifaceted within enterprise environments that rely on Mattermost for secure communications. An attacker who successfully exploits this vulnerability can gain unauthorized access to direct message conversations that should be restricted to specific participants, potentially leading to information disclosure, data exfiltration, or social engineering attacks. The ability to spoof direct message channels creates a persistent threat vector where malicious users can intercept private communications, impersonate legitimate users, or establish backdoors within the communication infrastructure. This vulnerability directly impacts the confidentiality and integrity of communications within the platform, undermining the trust model that organizations depend upon for secure collaboration.
Mitigation strategies for CVE-2019-20844 should prioritize immediate deployment of patched Mattermost Server versions that address the channel type validation flaw. Organizations should implement comprehensive monitoring of channel creation and modification activities through audit logs and API usage tracking to detect anomalous behavior patterns. Network segmentation and access control policies should be strengthened to limit exposure of Mattermost services to untrusted networks. The implementation of additional authentication layers and session management controls can help reduce the attack surface. Security teams should conduct thorough penetration testing and vulnerability assessments to identify any potential exploitation attempts that may have occurred prior to patching. According to ATT&CK framework category T1566 Credential Access, this vulnerability falls under the category of credential and session manipulation, where attackers can exploit system weaknesses to gain unauthorized access to protected resources. Organizations should also consider implementing automated patch management processes to ensure timely deployment of security updates across all instances of the Mattermost platform.