security.json is avialble under /infra-solr znode.
you can login to zkcli and verify the same.
# /usr/hdp/current/zookeeper-client/bin/zkCli.sh
[zk: localhost:2181(CONNECTED) 0] ls /
[registry, cluster, controller, brokers, zookeeper, infra-solr, admin, isr_change_notification, hiveserver2, controller_epoch, druid, rmstore, ambari-metrics-cluster, consumers, config]
[zk: localhost:2181(CONNECTED) 1] ls /infra-solr
[configs, overseer, aliases.json, live_nodes, collections, overseer_elect, security.json, clusterstate.json, clusterprops.json]
you can also verify it through Solr web UI.