It was found that Apache Solr would accept an object from an unauthenticated user that could be manipulated through subsequent post requests. An attacker could use this flaw to assemble an object that could permit execution of arbitrary code on the server.

Apache Solr versions 6.6.0 to 6.6.6, 7.0.0 to 7.7.3 and 8.0.0 to 8.6.2 prevents some features considered dangerous (which could be used for remote code execution) to be configured in a ConfigSet that's uploaded via API without authentication/authorization. The checks in place to prevent such features can be circumvented by using a combination of UPLOAD/CREATE actions.