Apache 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 Apache Solr 6.6.1 onwards.
CWE-287 - Improper Authentication
Improper (or broken) authentication attacks are widespread, and have accounted for many of the worst data breaches in recent years. Improper authentication attacks are a class of vulnerabilities where an attacker impersonates a legitimate user by exploiting weaknesses in either session management or credential management to gain access to the user’s account. This can result in disclosure of sensitive information, and can lead to system compromise, theft, identity theft, and fraud.