From my experience, dumping memory and most likely reverse engineering the binary is a must. Actually as it is legacy system, changes are this will be easier.

From my experience, dumping memory and most likely reverse engineering the binary is a must. Actually as it is legacy system, changes are this will be easier. To be honest, the path to follow mostly depends on the OS. As it is critical system, I would start with reverse engineering the binary, making sure the config is preserved across life time of application.