According to Apache log4j
"A security vulnerability, CVE-2019-17571 has been identified against Log4j 1. Log4j includes a SocketServer that accepts serialized log events and deserializes them without verifying whether the objects are allowed or not. This can provide an attack vector that can be expoited. Since Log4j 1 is no longer maintained this issue will not be fixed. Users are urged to upgrade to Log4j 2."