According to a couple of scanf docs I found, the '%x' format expects to write into unsigned int*, just as we already do. So it shouldn't be possible to overflow there.

The following line (or-ing all the values and checking that it's less than 256) handles the overflow already.

Limiting each %x specifier to two characters has exactly the same effect, and could potentially fix overflow errors in C runtimes that assume a larger destination without the data size prefix ('%zx' or '%llx'), but I don't know of any of those.

All that said, I'm not opposed to adding the tests. If the parsing logic is a sticking point, then that can be undone, but I think it's also okay.