Apache Solr is an independent full-text search server written in Java and running in a Servlet container (such as Apache Tomcat or Jetty). Apache Solr 5.0.0 to Apache Solr 8.3.1 are vulnerable to a Remote Code Execution through the VelocityResponseWriter. A Velocity template can be provided through Velocity templates in a configset velocity/
directory or as a parameter. A user-defined configset could contain renderable, potentially malicious, templates.
Attackers can use the Velocity-SSTI vulnerability to execute arbitrary code on the Solr system with the help of a custom Velocity template function
We recommend you to upgrade Apache Solr to the latest version.