static bool extract_if_dead(struct connectdata *conn,
                            struct Curl_easy *data)
{
  size_t pipeLen = conn->send_pipe.size + conn->recv_pipe.size;
  if(!pipeLen && !CONN_INUSE(conn)) {
    /* The check for a dead socket makes sense only if there are no
       handles in pipeline and the connection isn't already marked in
       use */
    bool dead;

    conn->data = data;
    if(conn->handler->connection_check) {
      /* The protocol has a special method for checking the state of the
         connection. Use it to check if the connection is dead. */
      unsigned int state;

      state = conn->handler->connection_check(conn, CONNCHECK_ISDEAD);
      dead = (state & CONNRESULT_DEAD);
    }
    else {
      /* Use the general method for determining the death of a connection */
      dead = SocketIsDead(conn->sock[FIRSTSOCKET]);
    }

    if(dead) {
      infof(data, "Connection %ld seems to be dead!\n", conn->connection_id);
      Curl_conncache_remove_conn(conn, FALSE);
      conn->data = NULL; /* detach */
      return TRUE;
    }
  }
  return FALSE;
}

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 Any operations using the original pointer are no longer valid because the memory belongs to the code that operates on the new pointer.