sir @pwuser164749502960 perhaps your vehicle under carriage is washed with brickish water. Please look for any other items under carriage with sign of corrosion. If it is only over the silver coated exhaust drum at external weld seams then the moisture in exhaust gases has corroded it completely from inside before showing up externally.
also check the coupling points of exhaust from manifold down below to tail end. If corroded it is highly recommended to swap the whole system. If it is only exhaust drum (as in picture) corroded, you may change that item soonest.