This indicates an attack attempt to exploit a Remote Code Execution Vulnerability in Pivotal Spring Framework.
The vulnerability is due to an error in the vulnerable application when handling a maliciously crafted request. A remote attacker may be able to exploit this to execute arbitrary code within the context of the application, via a crafted request.
Pivotal Spring Framework 4.3 to 4.3.14
Pivotal Spring Framework 5.0 to 5.0.4
Pivotal Spring Framework prior to 4.x
System Compromise: Remote attackers can gain control of vulnerable systems.
Apply the most recent upgrade or patch from the vendor: