CVE-2019-20889 in Mattermost Server
Summary
by MITRE
An issue was discovered in Mattermost Server before 5.7, 5.6.3, 5.5.2, and 4.10.5. It mishandles permissions for user-access token creation.
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Analysis
by VulDB Data Team • 10/25/2020
The vulnerability identified as CVE-2019-20889 represents a critical permission flaw within the Mattermost server authentication system that affects multiple versions including 5.7, 5.6.3, 5.5.2, and 4.10.5. This issue stems from inadequate access control mechanisms that allow unauthorized users to create user-access tokens through improper privilege validation. The flaw specifically impacts the server's token generation functionality where legitimate permission checks are bypassed, enabling malicious actors to escalate their privileges and gain unauthorized access to user accounts. Such vulnerabilities fall under the CWE-284 category of Improper Access Control, which is a fundamental security weakness that directly impacts the integrity and confidentiality of user data within the system.
The technical implementation of this vulnerability occurs at the authentication layer where the server fails to properly validate user permissions before allowing token creation operations. When users attempt to generate access tokens, the system should verify that the requesting user possesses the necessary administrative or authorization privileges to perform such actions. However, the flawed implementation allows any authenticated user to bypass these validation checks and create tokens that grant access to other user accounts or system resources. This misconfiguration creates a significant attack surface that can be exploited by both internal and external threat actors to gain unauthorized access to sensitive information and system functionality.
The operational impact of CVE-2019-20889 extends beyond simple privilege escalation as it enables persistent unauthorized access to user accounts and potentially the entire Mattermost deployment. Attackers can leverage this vulnerability to create tokens that maintain access even after initial exploitation, allowing for extended periods of unauthorized activity without detection. The vulnerability also impacts the system's ability to maintain proper audit trails and access logging since unauthorized token creation bypasses normal authentication monitoring mechanisms. This issue directly violates the principle of least privilege and can lead to data breaches, unauthorized communications, and potential system compromise that affects all users within the Mattermost environment.
Organizations affected by this vulnerability should implement immediate mitigations including applying the latest security patches released by Mattermost to address the permission validation flaw. System administrators should also review and strengthen their access control policies to ensure that token creation privileges are properly restricted to authorized administrators only. Network monitoring should be enhanced to detect unusual token creation patterns, and regular security audits should be conducted to identify any unauthorized access attempts. The ATT&CK framework categorizes this vulnerability under privilege escalation techniques where attackers can leverage weak access controls to gain elevated system privileges. Additionally, implementing proper input validation and access control mechanisms aligned with NIST cybersecurity frameworks will help prevent similar issues in the future and maintain the integrity of user authentication processes within the Mattermost platform.