Heap-based buffer overflow in the SOHM list-index deserialization code in HDF5 through 2.1.1 on all platforms allows attackers to cause a denial of service (crash) via a crafted HDF5 file whose shared-message list index declares a num messages count exceeding list max, triggering out-of-bounds heap reads and writes in H5SM cache list deserialize and H5SM cache list verify chksum.