OpenEXR is the reference implementation and specification for the EXR high-dynamic-range image file format, widely used in the motion picture industry. Versions 3.4.0 through 3.4.12 contain a NULL pointer dereference in the OpenEXRCore function exrattrsetbytes(). The public setter validates the top-level exrattrbytest value pointer but does not verify that the nested typehint pointer is non-NULL when hintlength is greater than zero. When a caller supplies a positive hintlength together with a NULL typehint, exrattrbytescreate() allocates a destination type-hint buffer and then copies from the NULL source pointer, causing a deterministic crash. The flaw is reachable through the public OpenEXRCore C API and results in a denial of service. The issue is fixed in version 3.4.13.