CVE-2019-20847 in Mattermost Server
Summary
by MITRE
An issue was discovered in Mattermost Server before 5.18.0. An attacker can send a user_typing WebSocket event to any channel.
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Analysis
by VulDB Data Team • 10/25/2020
The vulnerability identified as CVE-2019-20847 represents a significant security flaw in Mattermost Server versions prior to 5.18.0, where attackers can exploit a WebSocket communication channel to send user_typing events to any channel within the system. This issue stems from inadequate access controls and validation mechanisms within the WebSocket event handling functionality. The flaw allows malicious actors to manipulate real-time communication patterns by broadcasting typing indicators to channels they should not have access to, effectively enabling unauthorized participation in conversations and potential information disclosure.
This vulnerability manifests through the WebSocket protocol implementation where the server fails to properly authenticate or authorize WebSocket events before processing them. The user_typing event is designed to notify channel members when someone is typing a message, but the security mechanism that should restrict this functionality to authorized users is bypassed. Attackers can leverage this by establishing a WebSocket connection and sending crafted user_typing events to arbitrary channels, creating a false impression of user activity in channels they do not belong to. The flaw exists at the application layer and affects the integrity of real-time communication within the Mattermost platform.
The operational impact of this vulnerability extends beyond simple information disclosure, as it can enable more sophisticated attack vectors including social engineering, information gathering, and potential disruption of communication channels. An attacker could use this capability to create false activity patterns in sensitive channels, potentially misleading team members about ongoing discussions or to identify active users within specific channels. This manipulation of user typing indicators can also contribute to information leakage about channel membership and activity patterns, which may be exploited in conjunction with other reconnaissance activities. The vulnerability affects the overall trust and integrity of the communication system, as users cannot rely on the authenticity of typing indicators.
The security implications of CVE-2019-20847 align with CWE-284, which addresses improper access control, and can be mapped to ATT&CK technique T1078 for valid accounts usage and T1566 for credential access through social engineering. Organizations should immediately upgrade to Mattermost Server version 5.18.0 or later to address this vulnerability. Additional mitigations include implementing network-level restrictions on WebSocket connections, monitoring for unusual WebSocket activity patterns, and ensuring proper authentication mechanisms are in place for all WebSocket event handling. Administrators should also review and tighten access controls for channels and ensure that WebSocket communication is properly authenticated and authorized before processing any events, as this vulnerability demonstrates the critical importance of validating all incoming communication in real-time systems.