Are all corrosives either acids or bases?
Wikipedia lists many corrosive compounds.  While a lot of them function as strong acids or bases, there are also these (not an exhaustive list):


Strong oxidizers including concentrated hydrogen peroxide
Fluorides (they say "fluoride ion", so salts as well as the acid are meant)
Organic compounds that can act as alkylating agents such as methyl sulfate


The moral of the story: Hazards can't be pigeonholed into specific types of chemicals.  Best to find and read the safety data sheet with any chemical.