CVE-2026-43905: OpenImageIO: JPEG2000 (OpenJPH) signed integer overflow in buffer allocation

OpenImageIO is a toolset for reading, writing, and manipulating image files of any image file format relevant to VFX / animation. Prior to 3.0.18.0 and 3.1.13.0, jpeg2000input.cpp:395 computes buffer size as const int bufsize = w * h * ch * buffer_bpp using signed 32-bit arithmetic. When the product exceeds INT_MAX, the result wraps to 0 or a small value. m_buf.resize() allocates an undersized buffer, and subsequent pixel write loops cause heap overflow. Conditional on USE_OPENJPH build flag. This vulnerability is fixed in 3.0.18.0 and 3.1.13.0.