CVE-2019-20864 in Mattermost Plugins
Summary
by MITRE
An issue was discovered in Mattermost Plugins before 5.13.0. The GitHub plugin allows an attacker to attach his Mattermost account to a different person's GitHub account.
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Analysis
by VulDB Data Team • 10/25/2020
The vulnerability described in CVE-2019-20864 represents a critical authentication and authorization flaw within the Mattermost collaboration platform's plugin architecture. This issue specifically affects the GitHub plugin component and exists in versions prior to 5.13.0, creating a scenario where malicious actors can exploit the plugin's account linking mechanism to associate their own Mattermost user credentials with another individual's GitHub account. The flaw essentially undermines the integrity of user identity verification within the integrated ecosystem, allowing unauthorized access to GitHub resources through compromised Mattermost accounts.
The technical nature of this vulnerability stems from inadequate validation and verification processes during the account linking procedure between Mattermost and GitHub platforms. When users attempt to connect their GitHub accounts to Mattermost through the plugin interface, the system fails to properly authenticate that the person initiating the connection is indeed the legitimate owner of the target GitHub account. This weakness creates a path for privilege escalation attacks where an attacker can manipulate the account association process to gain unauthorized access to another user's GitHub repositories, issues, and other collaborative resources. The vulnerability aligns with CWE-287, which addresses authentication failures, and represents a direct violation of proper access control mechanisms that should prevent unauthorized account linking operations.
The operational impact of this vulnerability extends beyond simple unauthorized access to encompass potential data breaches, intellectual property exposure, and compromise of sensitive development workflows. Organizations relying on Mattermost for team collaboration and code management may experience significant security implications when attackers exploit this flaw to gain access to private repositories, view confidential project information, or manipulate development environments. The attack vector is particularly concerning because it operates within the legitimate plugin interface, making detection more challenging for security monitoring systems. This vulnerability also demonstrates the broader risks associated with third-party plugin integrations in enterprise collaboration platforms, where insufficient security controls in individual components can compromise the entire system's security posture.
Organizations should immediately upgrade to Mattermost version 5.13.0 or later to remediate this vulnerability, as the fix addresses the core account linking validation mechanism that was previously bypassable. Security teams should also implement monitoring for unusual account linking activities within their Mattermost environments and conduct regular audits of plugin configurations to ensure that only authorized users can establish external account connections. Additional mitigations include implementing multi-factor authentication for all Mattermost accounts, restricting plugin installation permissions to administrative users only, and establishing clear policies for account linking procedures. From an ATT&CK framework perspective, this vulnerability maps to techniques involving privilege escalation and credential access, specifically leveraging the initial access through the plugin interface to expand attack capabilities. Organizations should also consider implementing network segmentation controls to limit the potential lateral movement that could occur if attackers successfully exploit this vulnerability to gain access to connected GitHub resources.