The issue is related to the exposure of sensitive information to an unauthorized actor in Apache Solr. Solr Streaming Expressions allows users to extract data from other Solr Clouds using a `zkHost` parameter. When the original SolrCloud is set up to use ZooKeeper credentials and ACLs, they will be sent to whatever `zkHost` the user provides. An attacker could set up a server to mock ZooKeeper, accepting ZooKeeper requests with credentials and ACLs, and extract sensitive information. Then, they could send a streaming expression using the mock server's address in `zkHost`. Streaming Expressions are exposed via the "/streaming" handler with "read" permissions.