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 Java CLI when handling serialized Java SignedObject objects. A remote attacker could exploit this to execute arbitrary code within the context of the application, via a crafted request.
Jenkins LTS before 2.46.2
Jenkins-Ci Jenkins before 2.57
System Compromise: Remote attackers can gain control of vulnerable systems.
Refer to the vendor's advisory for updates: