How to find the leak in a basement?
I can see some cracks in the cement at the top of the drain. it looks like the drain is full of debris is it draining properly? If the drain is plugged or partially obstructed the water may be backing up enough and flowing through the cracks. Sealing the cracks with hydraulic cement (outside the house) will reduce the amount of water escaping the box and that should reduce the water entering the basement. Make sure to seal the cracks all the way to the bottom if they extend that far down I cant tell in the photo.