About the Unsuccessful Quest for a Deserialization Gadget (or: How I found CVE-2021-21481)

This blog post describes the research on SAP J2EE Engine 7.50 I did between October 2020 and January 2021. The first part describes how I set off to find a pure SAP deserialization gadget, which would allow to leverage SAP's P4 protocol for exploitation, and how that led me, by sheer coincidence, to an entirely unrelated, yet critical vulnerability, which is outlined in part two.

The reader is assumed to be familiar with Java Deserialization and should have a basic understanding of Remote Method Invocation (RMI) in Java.