same here. it was working up til a few days ago. I can tell the front cam still works as I can see it in the settings for skin tone, as well as other apps that use the front cam. once I switch to the back cam those apps fail too.
this has to be a firmware issue. I doubt all of us suddenly have a physical cam issue (albeit I suppose it's possible).
I m also facing same problem but the reason might be the different. However the troubleshoot must have work. If it is not working than the problem us with your handset. Please check your smartphone by an expert.