There are two distinct versions of the CUCM 12.5 ISO. It is vital to select the correct one based on your deployment region:
12.5 focuses on simplifying admin and enhancing security. To make this story more useful for you, could you tell me: cucm 12.5 bootable iso download
Open the non-bootable ISO and locate the isolinux folder. Extract the isolinux.bin file. There are two distinct versions of the CUCM 12