Hessian serialization is a network protocol that supports object-based transmission. Apache Cayenne's optional Remote Object Persistence (ROP) feature is a web services-based technology that provides object persistence and query functionality to 'remote' applications. In Apache Cayenne 4.1 and earlier, running on non-current patch versions of Java, an attacker with client access to Cayenne ROP can transmit a malicious payload to any vulnerable third-party dependency on the server. This can result in arbitrary code execution.

Deserialization of untrusted data in Apache Cayenne