How to ensure security in the "64-bit program + 32-bit COM proxy" combination?

Question

Windows

There is a 64-bit program that communicates with a 32-bit accounting system via COM. In order for this to somehow work, we made a "proxy" - a 32-bit program that, through a regular console in XML format, transmits data to a 64-bit "mother". The accounting system checks which program it is contacting, but, of course, it sees a proxy, not a mother.
Theoretically, such a data leak is possible: the malware launches a proxy and pulls data as much as you like. What sysadmin and programmer measures are best taken against such a case?
So far, the only defense against this is the “elusive Joe.” Switching to 64-bit COM is impossible - the developers of the accounting system simply did not provide a COM server.

Answer 1

Again I have to answer myself.
Win32: Who called the program?

Answer 2

Theoretically, such a data leak is possible: the malware launches a proxy and pulls data as much as it pleases. What sysadmin and programmer measures are best taken against such a case?

Theoretically, data leakage is always possible.
No one knows how critical this is for you and whether you need to take measures at all, and what kind of measures you need to take.

Answer 3

Make the interaction through Pipe.
Set up an ACL for pipe.