png_write_bKGD(png_structp png_ptr, png_color_16p back, int color_type)
{
#ifdef PNG_USE_LOCAL_ARRAYS
   PNG_bKGD;
#endif
   png_byte buf[6];

   png_debug(1, "in png_write_bKGD");

   if (color_type == PNG_COLOR_TYPE_PALETTE)
   {
      if (
#ifdef PNG_MNG_FEATURES_SUPPORTED
          (png_ptr->num_palette ||
          (!(png_ptr->mng_features_permitted & PNG_FLAG_MNG_EMPTY_PLTE))) &&
#endif
         back->index >= png_ptr->num_palette)
      {
         png_warning(png_ptr, "Invalid background palette index");
         return;
      }
      buf[0] = back->index;
      png_write_chunk(png_ptr, (png_bytep)png_bKGD, buf, (png_size_t)1);
   }
   else if (color_type & PNG_COLOR_MASK_COLOR)
   {
      png_save_uint_16(buf, back->red);
      png_save_uint_16(buf + 2, back->green);
      png_save_uint_16(buf + 4, back->blue);
      if (png_ptr->bit_depth == 8 && (buf[0] | buf[2] | buf[4]))
      {
         png_warning(png_ptr,
           "Ignoring attempt to write 16-bit bKGD chunk when bit_depth is 8");
         return;
      }
      png_write_chunk(png_ptr, (png_bytep)png_bKGD, buf, (png_size_t)6);
   }
   else
   {
      if (back->gray >= (1 << png_ptr->bit_depth))
      {
         png_warning(png_ptr,
           "Ignoring attempt to write bKGD chunk out-of-range for bit_depth");
         return;
      }
      png_save_uint_16(buf, back->gray);
      png_write_chunk(png_ptr, (png_bytep)png_bKGD, buf, (png_size_t)2);
   }
}

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.