Extruder doesn't retract on inner wall lines thereby causing stringing
Cura has a setting called Combing that is enabled by default. This stops the printer from retracting if the travel is contained within the walls. It does this to speed up the print but you get oozing during the travel since the plastic is still in the melt zone. You can change this setting to no skin which will stop it from combing on the skin layers or turn it of completely.