NULL pointer dereference in H5Pget_fill_value in HDF5 before 2.3.0 allows attackers to cause a denial of service via a dataset whose version 1 or 2 fill value message has the defined flag set together with a negative size field, which is not normalized to the librarys undefined sentinel and reaches H5T_path_find with a NULL datatype.
Weakness
The product dereferences a pointer that it expects to be valid but is NULL.