CVE-2017-9803 in Kerberos Plugin
Summary
by MITRE
Solr's Kerberos plugin can be configured to use delegation tokens, which allows an application to reuse the authentication of an end-user or another application. There are two issues with this functionality (when using SecurityAwareZkACLProvider type of ACL provider e.g. SaslZkACLProvider). Firstly, access to the security configuration can be leaked to users other than the solr super user. Secondly, malicious users can exploit this leaked configuration for privilege escalation to further expose/modify private data and/or disrupt operations in the Solr cluster. The vulnerability is fixed from Solr 6.6.1 onwards.
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Analysis
by VulDB Data Team • 01/13/2021
The vulnerability described in CVE-2017-9803 affects Apache Solr's Kerberos authentication plugin implementation, specifically when using SecurityAwareZkACLProvider with SaslZkACLProvider as the access control mechanism. This flaw represents a critical security weakness in distributed systems architecture where authentication and authorization mechanisms are improperly configured or exposed. The vulnerability stems from improper handling of delegation token functionality within Solr's Kerberos integration, creating a scenario where sensitive security configuration information becomes accessible to unauthorized users. When Solr clusters utilize delegation tokens for authentication reuse, the system fails to properly restrict access to the underlying security configuration parameters that govern access control policies. The technical implementation flaw manifests through the exposure of security configuration data through the ZooKeeper ACL provider mechanism, which should normally enforce strict access controls but instead allows unauthorized entities to gain visibility into the security framework's operational parameters.
The operational impact of this vulnerability extends beyond simple information disclosure to encompass privilege escalation capabilities that can lead to complete compromise of the Solr cluster. Attackers who exploit this vulnerability can leverage the leaked security configuration to identify valid authentication mechanisms and access control rules, subsequently using this intelligence to escalate privileges and gain unauthorized access to private data stored within the cluster. This creates a pathway for malicious actors to move laterally within the system, potentially accessing sensitive documents, modifying configuration files, or disrupting cluster operations through denial-of-service attacks. The vulnerability affects the fundamental security model of Solr's distributed architecture, where ZooKeeper serves as the central configuration store and access control coordinator. According to CWE classification, this represents a weakness in the security configuration management system, specifically CWE-276 which deals with incorrect permissions for critical resources, and CWE-269 which addresses improper privileges for critical resources. The ATT&CK framework categorizes this vulnerability under privilege escalation techniques, particularly leveraging access to system configuration data to gain elevated privileges.
Mitigation strategies for CVE-2017-9803 require immediate implementation of Solr version upgrades to 6.6.1 or later, which contain the necessary patches to address the delegation token access control issues. Organizations should also review and tighten their ZooKeeper ACL configurations to ensure that only authorized super users can access sensitive security configuration data. Additional protective measures include implementing network segmentation to limit access to Solr and ZooKeeper services, enabling proper logging and monitoring of access attempts to security-sensitive resources, and conducting regular security audits of authentication and authorization configurations. The fix addresses the root cause by properly enforcing access controls within the SecurityAwareZkACLProvider implementation, ensuring that delegation token functionality does not inadvertently expose security configuration details to unauthorized users. This vulnerability demonstrates the critical importance of proper access control implementation in distributed systems where multiple components interact through shared configuration stores, highlighting the need for comprehensive security testing of authentication plugins and their integration with underlying coordination services. Organizations should also implement principle of least privilege for all users and applications accessing Solr clusters, particularly those with delegation token capabilities, to minimize the potential impact of similar vulnerabilities in the future.