in zipimport.c
  1116     bytes_size = compress == 0 ? data_size : data_size + 1;
  1117     if (bytes_size == 0)
  1118         bytes_size++;
  1119     raw_data = PyBytes_FromStringAndSize((char *)NULL, bytes_size);

If compress != 0, then bytes_size = data_size + 1
data_size is not sanitized, so if data_size = -1, then it overflows and becomes 0.
In that case bytes_size becomes 1 and python allocates small heap, but after that in fread, it overflows heap.