Can cashews go bad? If so, how do you tell? We have a tub of cashews that seems "off:" they smell a little different and taste a little different than we're used to.

They don't smell or taste rancid (to us, I don't think I've ever tried cashews that were old enough to possibly be rancid) but I'm wondering if there can be any other type of degredation in them.  e.g. I've read that peanuts can get a sort of mold growing on them that's not good for you.
It is possible for mold to form on cashews - or any other nuts - but only if there has been moisture penetration into the container. If the moisture is at a safe (low) level, then mold won't grow.

See for example, Mycology and spoilage of retail cashew nuts, which refers to the maximum acceptable moisture content of 5.8% for retail storage/shipping, although if you look at their data table, it appears that you may still end up with non-trivial amounts of mold in the low 5% range (which is why you are supposed to store nuts sealed and in a cool, dry place).

Honestly, cashews are hard enough such that you would almost certainly see mold on the surface if it were present in harmful quantities. Most likely what you're smelling/tasting is simply oxidation of the fats (the process which causes rancidity) without actual full-blown rancidity. Mold requires moisture but all oxidation requires is light and maybe a little air exposure.

If you really want to be on the safe side - e.g. if your home is particularly hot or humid - then store your nuts in the refrigerator or freezer (sealed, to prevent contamination or off-odours). Although most (all?) nuts are considered shelf-stable, they do keep longer in the fridge or freezer.