png_write_pHYs(png_structp png_ptr, png_uint_32 x_pixels_per_unit,
   png_uint_32 y_pixels_per_unit,
   int unit_type)
{
#ifdef PNG_USE_LOCAL_ARRAYS
   PNG_pHYs;
#endif
   png_byte buf[9];

   png_debug(1, "in png_write_pHYs");

   if (unit_type >= PNG_RESOLUTION_LAST)
      png_warning(png_ptr, "Unrecognized unit type for pHYs chunk");

   png_save_uint_32(buf, x_pixels_per_unit);
   png_save_uint_32(buf + 4, y_pixels_per_unit);
   buf[8] = (png_byte)unit_type;

   png_write_chunk(png_ptr, (png_bytep)png_pHYs, buf, (png_size_t)9);
}

The product performs operations on a memory buffer, but it reads from or writes to a memory location outside the buffer's intended boundary. This may result in read or write operations on unexpected memory locations that could be linked to other variables, data structures, or internal program data.