static MagickBooleanType DecodeImage(const unsigned char *compressed_pixels,
  const size_t length,unsigned char *pixels,size_t maxpixels)
{
  register const unsigned char
    *l,
    *p;

  register unsigned char
    *q;

  ssize_t
    count;

  unsigned char
    byte;

  (void) LogMagickEvent(TraceEvent,GetMagickModule(),"...");
  assert(compressed_pixels != (unsigned char *) NULL);
  assert(pixels != (unsigned char *) NULL);
  p=compressed_pixels;
  q=pixels;
  l=q+maxpixels;
  while (((size_t) (p-compressed_pixels) < length) && (q < l))
  {
    byte=(*p++);
    if (byte != 128U)
      *q++=byte;
    else
      {
        /*
          Runlength-encoded packet: <count><byte>
        */
        count=(ssize_t) (*p++);
        if (count > 0)
          byte=(*p++);
        while ((count >= 0) && (q < l))
        {
          *q++=byte;
          count--;
        }
     }
  }
  return(MagickTrue);
}

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.