Apache ActiveMQ uses LocateRegistry.createRegistry() to create the JMX RMI registry and binds the server to the "jmxrmi" entry. It is possible to connect to the registry without authentication and call the rebind method to rebind jmxrmi to something else. If an attacker creates another server to proxy the original, and bound that, he effectively becomes a man in the middle and is able to intercept the credentials when an user connects. Upgrade to Apache ActiveMQ 5.15.12.
Xstream API versions up to 1.4.6 and version 1.4.10, if the security framework has not been initialized, may allow a remote attacker to run arbitrary shell commands by manipulating the processed input stream when unmarshaling XML or any supported format. e.g. JSON.