A long time ago, when I was a kid without any money, I band-aided a few holes in mufflers like that for short term fixes for myself and some friends. I'd grind off the rust, stuff the hole with 0000 steel wool, and then put a couple coats of JB weld over it. The steel would act as a backing for the JBW sort of like fiberglass for Bondo, then burn away inside (I think). It worked pretty well actually as JB is pretty hard and heat resistant. Definitely not a permanent fix, but got me by when I needed it.
Given the looks of the pipes, you really need to replace asap though.
Given the looks of the pipes, you really need to replace asap though.