Acid Exhaust ?

[Fix_It]

after taking my daughter sledding this morning , i found the rear corner of my truck bumper totally eaten up with rust and pealing the chrome up and other areas showing rust coming through ..this is only where the black soot from the exhaust touched .. i just washed the truck 3 days ago and never saw this ..and its not a small patch ...

its even hitting the clear coat on the truck bed corner .. the truck is only a year old ..

would this happen if the cat not function properly ?

this is on my 06 cu mmins ..