Can cashews go bad? If so, how do you tell?
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.