We've been noticing this problem with Solr version 5.4.1 and it's still the case for the version 6.6.0. The problem is that we're using SolrCloud with secured Zookeeper and our users are granted access to Solr Admin GUI, and, at the same time, they are not supposed to have access to Zookeeper credentials, i.e. usernames and passwords. However, we (and some of our users) have found out that Zookeeper credentials are displayed on at least two sections of the Solr Admin GUI, i.e. "Dashboard" and "Java Properties".
Could you please consider for the future Solr releases removing the Zookeeper parameters mentioned above from the output of these URLs and from other URLs that contain this information in their output, if there are any besides the ones mentioned? We find that it is be pretty challenging (and probably impossible) to restrict users from accessing some particular paths with security.json mechanism, and we think that that would be beneficial for overall Solr security to hide Zookeeper credentials.
Thank you so much for your consideration!