The libcap internal function for validating cap_t and cap_iab_t values up to and including libcap-2.54 contained code to protect the validation from NULL pointers. Between libcap-2.55 and libcap-2.58 inclusive, this protection was dropped. We will add it back in libcap-2.59.
Fixed in: https://git.kernel.org/pub/scm/libs/libcap/libcap.git/commit/?id=6643c636e8ab44add497f97e479ad8a931d43adf