There are 2 open security issues in buster.
1 important issue:
The optional ActiveMQ LDAP login module can be configured to use anonymous access to the LDAP server. In this case, for Apache ActiveMQ Artemis prior to version 2.16.0 and Apache ActiveMQ prior to versions 5.16.1 and 5.15.14, the anonymous context is used to verify a valid users password in error, resulting in no check on the password.
1 issue left for the package maintainer to handle:
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.
You can find information about how to handle this issue in the security team's documentation.