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 nummessages count exceeding listmax, triggering out-of-bounds heap reads and writes in H5SMcachelistdeserialize and H5SMcachelistverify_chksum.