In the Spring I fixed 3 of these holes in mine. Been several months now and is holding up great. Clean up the holes as much as possible with a wire brush/screw driver/Dremel to get any loose rust off so you have a solid area to work with. You may have to rip off the heat shield around the converter to get at the hole. Nothing a pry bar and vice grip can't handle. Once cleaned, find a short stubby screw that will fit and bite into the hole. If the hole is bigger than the screw, add some metal screen or washers to fill most of the gap. Once you feel the hole is mostly plugged with your desired screw/washer/screen combo go ahead on apply the leak stop putty. I used what I found on the shelf at Autozone, was about $4 (see below). Apply the putty to the areas making sure it gets squeezed into the gaps and holes around the screw to give you something solid to bond and hold onto. Let it dry for an hour or two starting the truck for about 45 seconds at some point to add some heat and aid the drying process. After driving as normal the next day, you may notice the putty has cracks and shrunk into the hold a little. Add more putty and fill in any cracks, let dry and you should be good to go.

 

Believe it or not, there is sealer on the market that is rated for 2300 degrees.
The way exhaust is repaired depends on the method because high heat and exhaust pressure needs to be considered for support.
The high temp. sealer comes in a small container.
Found it at Advance Auto.
One basic thing to remember is not to apply then start engine and blow a hole in the material.
Exhaust manifolds and Cats get into the 600 degree range.

 

I had a cracked exhaust, and I used my Hobart to fix it in 30 seconds.