OpenEXR is the reference implementation and specification for the EXR image format, widely used in the motion picture industry. From version 3.4.0 through 3.4.12, the HTJ2K decoder parses a header-length field (PLEN) from a chunk's compressed data but never checks that this value fits within the available buffer before using it. When decoding, it advances the codestream pointer by the attacker-supplied header size and passes the resulting offset and remaining length to the OpenJPH memory-input path, so a crafted value pushes the pointer past the end of the buffer and causes an out-of-bounds read. Because this field comes straight from attacker-controlled EXR chunk data, the flaw is reachable during normal decoding of an untrusted file. This issue is fixed in version 3.4.13.