NET+OS Upgrade

I have some rather old custom firmware running on ConnectME CF/W devices (P/N (1P) 50000878-03 H) built using NET+OS 6.0e with GNU tools. Recently, there was an issue with a TCP server running on the devices and I was wondering if a NET+OS upgrade would help.

So, my question is, what’s the latest version of NET+OS/GNU that supports these devices and how do I get it?