CVE-2019-13423 in Search Guard Plugin
Summary
by MITRE
Search Guard Kibana Plugin versions before 5.6.8-7 and before 6.x.y-12 had an issue that an authenticated Kibana user could impersonate as kibanaserver user when providing wrong credentials when all of the following conditions a-c are true: a) Kibana is configured to use Single-Sign-On as authentication method, one of Kerberos, JWT, Proxy, Client certificate. b) The kibanaserver user is configured to use HTTP Basic as the authentication method. c) Search Guard is configured to use an SSO authentication domain and HTTP Basic at the same time
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Analysis
by VulDB Data Team • 08/04/2020
The vulnerability identified as CVE-2019-13423 affects the Search Guard Kibana plugin, specifically targeting versions prior to 5.6.8-7 and 6.x.y-12. This security flaw represents a critical authentication bypass issue that undermines the integrity of the plugin's access control mechanisms. The vulnerability arises from a misconfiguration scenario involving multiple authentication methods that creates an unexpected interaction between Single-Sign-On (SSO) and HTTP Basic authentication domains. The flaw demonstrates a classic case of improper authentication handling where the system fails to properly validate user credentials when multiple authentication methods are simultaneously configured.
The technical implementation of this vulnerability stems from the plugin's failure to correctly enforce authentication boundaries when multiple authentication domains are active. When an authenticated Kibana user attempts to access resources while providing incorrect credentials, the system's logic incorrectly allows the user to assume the identity of the kibanaserver user. This occurs specifically when the system is configured with SSO authentication methods such as Kerberos, JWT, Proxy, or Client certificate, while simultaneously maintaining HTTP Basic authentication for the kibanaserver user. The interaction between these authentication domains creates a logical flaw in the authentication flow where credential validation becomes inconsistent and predictable.
The operational impact of this vulnerability is severe as it allows authenticated users to escalate their privileges and impersonate the kibanaserver user, which typically possesses elevated system-level permissions. The kibanaserver user usually has critical access to core Kibana functionalities and system configurations, making this privilege escalation particularly dangerous. Attackers could potentially access sensitive data, modify system configurations, or perform administrative actions that should be restricted to authorized personnel only. This vulnerability directly violates the principle of least privilege and can lead to complete system compromise when combined with other exploitation techniques.
The root cause of this vulnerability can be classified under CWE-287 - Improper Authentication, specifically addressing issues related to authentication bypass through improper session management. The flaw aligns with ATT&CK technique T1078.004 - Valid Accounts: Kerberos Ticketing, as it exploits the interaction between different authentication mechanisms within the same system. Organizations using Search Guard with mixed authentication methods face significant risk as this vulnerability requires minimal user interaction to exploit and can remain undetected for extended periods. The vulnerability also demonstrates poor separation of concerns in authentication domain management, where the system fails to properly isolate authentication flows between different user contexts.
Mitigation strategies should focus on immediate configuration changes to eliminate the conflicting authentication setup that enables this vulnerability. Organizations must ensure that either SSO authentication or HTTP Basic authentication is used exclusively rather than simultaneously. The recommended approach involves reconfiguring the Search Guard plugin to use only one authentication method for all user contexts, with proper authentication domain separation. Additionally, implementing proper access controls and monitoring for unusual authentication patterns can help detect exploitation attempts. Regular security audits of authentication configurations should be conducted to prevent similar misconfigurations. System administrators should also consider implementing additional security layers such as network segmentation and comprehensive logging to detect unauthorized access attempts. The vulnerability highlights the importance of thorough testing of authentication logic when multiple security mechanisms are combined, emphasizing the need for proper security configuration management practices.