Apache Solr uses a PKI based mechanism to secure inter-node communication when security is enabled. It is possible to create a specially crafted node name that does not exist as part of the cluster and point it to a malicious node. This can trick the nodes in cluster to believe that the malicious node is a member of the cluster. So, if Solr users have enabled BasicAuth authentication mechanism using the BasicAuthPlugin or if the user has implemented a custom Authentication plugin, which does not implement either "HttpClientInterceptorPlugin" or "HttpClientBuilderPlugin", his/her servers are vulnerable to this attack. Users who only use SSL without basic authentication or those who use Kerberos are not affected. References: http://mail-archives.us.apache.org/mod_mbox/www-announce/201707.mbox/%3CCAOOKt53EgrybaD%2BiSn-nBbvFdse-szhg%3DhMoDZuvUvyMme-Z%3Dg%40mail.gmail.com%3E Upstream patch: http://git-wip-us.apache.org/repos/asf/lucene-solr/commit/2f5ecbcf
Upstream issue: https://issues.apache.org/jira/browse/SOLR-10624 References: http://seclists.org/bugtraq/2017/Jul/15