Incorrect Control Flow Scoping

Demonstrations

The following examples help to illustrate the nature of this weakness and describe methods or techniques which can be used to mitigate the risk.

Note that the examples here are by no means exhaustive and any given weakness may have many subtle varieties, each of which may require different detection methods or runtime controls.

Example One

The following example attempts to resolve a hostname.

protected void doPost (HttpServletRequest req, HttpServletResponse res) throws IOException {
  String ip = req.getRemoteAddr();
  InetAddress addr = InetAddress.getByName(ip);
  ...
  out.println("hello " + addr.getHostName());
}

A DNS lookup failure will cause the Servlet to throw an exception.

Example Two

This code queries a server and displays its status when a request comes from an authorized IP address.

$requestingIP = $_SERVER['REMOTE_ADDR'];
if(!in_array($requestingIP,$ipAllowList)){
  echo "You are not authorized to view this page";
  http_redirect($errorPageURL);
}
$status = getServerStatus();
echo $status;
...

This code redirects unauthorized users, but continues to execute code after calling http_redirect(). This means even unauthorized users may be able to access the contents of the page or perform a DoS attack on the server being queried. Also, note that this code is vulnerable to an IP address spoofing attack (CWE-212).

Example Three

Included in the doPost() method defined below is a call to System.exit() in the event of a specific exception.

Public void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
  try {
    ...
  } catch (ApplicationSpecificException ase) {
    logger.error("Caught: " + ase.toString());
    System.exit(1);
  }
}

See Also