Sounds like a hardware issue. Do a full wipe and restore to stock ucmc1 and try again. If switching to front camera freezes and crashes out of the camera app then it is hardware.
Buy a front camera off eBay, watch a YouTube video if you haven't opened one of these phones so you don't break anything, and finally swap it out!
Sent from my SAMSUNG-SGH-I727 using xda app-developers app