A heap-based buffer overflow in H5VM_array_fill() in src/H5VM.c in HDF5 before 2.2.0 lets a remote attacker cause an application crash and possibly execute arbitrary code with a crafted HDF5 file. When a dataset's unallocated chunks are read, H5D__fill_init() fills the fill-value buffer from datatype and dataspace metadata in the file. If that metadata is inconsistent with the buffer's allocated size, the write goes past the end of the buffer. The attacker can control the content written through the fill value stored in the file.