This indicates an attack attempt to exploit a Denial of Service Vulnerability in Apache Log4j.
The vulnerability is due to insufficient sanitizing of user supplied inputs in the application. A remote attacker could exploit these vulnerabilities by sending a crafted request to the target server. Successful exploitation could result in a denial-of-service condition.
Apache Log4j 2.0-beta9 prior to 2.17.0
Denial of Service: Remote attackers can crash vulnerable systems.
Apply the most recent upgrade or patch from the vendor.