This indicates an attack attempt to exploit a remote Code Execution vulnerability in Jenkins CI Server.
The vulnerability is due to an error in the vulnerable application when handling a maliciously crafted request. A remote attacker may be able exploit this to execute arbitrary code within the context of the application via crafted requests.
Jenkins Jenkins 1.649 and prior
Jenkins Jenkins LTS releases 1.642.1 and prior
System Compromise: Remote attackers can gain control of vulnerable systems
Apply the most recent upgrade or patch from the vendor.