Breaking hash functions is in NP, but isn't expected to be NP-complete, meaning that you can't easily encode eg a SAT problem into a hash function, such that breaking the hash solves the SAT problem.
You can do the reverse (encode the hash into a SAT problem), but that's possible for any NP problem, because SAT is NP-complete.
You can do the reverse (encode the hash into a SAT problem), but that's possible for any NP problem, because SAT is NP-complete.