This indicates an attack attempt to exploit a Remote Code Execution Vulnerability in Apache Log4j.
The vulnerability is due to insufficient sanitizing of user supplied inputs in the application. A remote attacker may be able to exploit this to execute arbitrary code within the context of the application.
Apache Log4j before version 2.16
Apache Log4j version 1.2
System Compromise: Remote attacker can gain control of vulnerable systems.
Apply the most recent upgrade or patch from the vendor