MagickExport int ReadBlobByte(Image *image)
{
  BlobInfo
    *magick_restrict blob_info;

  register const unsigned char
    *p;

  unsigned char
    buffer[1];

  assert(image != (Image *) NULL);
  assert(image->signature == MagickCoreSignature);
  assert(image->blob != (BlobInfo *) NULL);
  assert(image->blob->type != UndefinedStream);
  blob_info=image->blob;
  switch (blob_info->type)
  {
    case StandardStream:
    case FileStream:
    case PipeStream:
    {
      int
        c;

      p=(const unsigned char *) buffer;
      c=getc(blob_info->file_info.file);
      if (c == EOF)
        return(EOF);
      *buffer=(unsigned char) c;
      break;
    }
    default:
    {
      ssize_t
        count;

      p=(const unsigned char *) ReadBlobStream(image,1,buffer,&count);
      if (count != 1)
        return(EOF);
      break;
    }
  }
  return((int) (*p));
}

The product reuses or references memory after it has been freed. At some point afterward, the memory may be allocated again and saved in another pointer, while the original pointer references a location somewhere within the new allocation. Any operations using the original pointer are no longer valid because the memory belongs to the code that operates on the new pointer.