I was fixing my blocked sunroof drains on my 2010 CTS wagon.Make repairs to the sunroof drains first... See if issue goes away. Will be a bit of a pain accessing the drivers side but you really need to start there. There should be no way for the rails to leak through unless something was damaged. Mine only have one of those holes per side but I don't even have the rubber on my rails with the bike rack mounted there. Those rails are riveted to the roof and if there is a leak somewhere from those rails the vehicle must have been in an accident that wasn't repaired properly or some other issue such as rusted through hole or something that you can't see.
I strongly suspect it is the drains on your car. If you want to see otherwise you may have to drop the headliner and pour water on the rails and see where it is coming through and end up having to fix from underneath. You may find it easiest to drop the headliner by the rear lift gate and look there.
This video is very good for the front drain pipes:
The right hand side can be accessed by removing the rear wheel liner.
You will see a big grommet with a cable coming out towards the upper rear of the wheel arch. Pull the whole grommet out and you will see the pipe inserted into the back of it. Make sure you scoop out all the muck inside the grommet where the pipe was inserted and run a weed whacked line up the drain pipe. Both were full of muck.
You can undo the four bolts holding the rear stationary sunroof to gain access to the drain holes and slide it an inch forward out of the way. No need to drop the roof lining.