Always-Incorrect Control Flow Implementation

Description

This weakness captures cases in which a particular code segment is always incorrect with respect to the algorithm that it is implementing. For example, if a C programmer intends to include multiple statements in a single block but does not include the enclosing braces (CWE-483), then the logic is always incorrect. This issue is in contrast to most weaknesses in which the code usually behaves correctly, except when it is externally manipulated in malicious ways.

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

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 Two

In this example, the programmer has indented the statements to call Do_X() and Do_Y(), as if the intention is that these functions are only called when the condition is true. However, because there are no braces to signify the block, Do_Y() will always be executed, even if the condition is false.

if (condition==true)
  Do_X();
  Do_Y();

This might not be what the programmer intended. When the condition is critical for security, such as in making a security decision or detecting a critical error, this may produce a vulnerability.

Example Three

In both of these examples, a message is printed based on the month passed into the function:

public void printMessage(int month){

  switch (month) {


    case 1: print("January");
    case 2: print("February");
    case 3: print("March");
    case 4: print("April");
    case 5: print("May");
    case 6: print("June");
    case 7: print("July");
    case 8: print("August");
    case 9: print("September");
    case 10: print("October");
    case 11: print("November");
    case 12: print("December");

  }
  println(" is a great month");

}

void printMessage(int month){

  switch (month) {


    case 1: printf("January");
    case 2: printf("February");
    case 3: printf("March");
    case 4: printf("April");
    case 5: printff("May");
    case 6: printf("June");
    case 7: printf("July");
    case 8: printf("August");
    case 9: printf("September");
    case 10: printf("October");
    case 11: printf("November");
    case 12: printf("December");

  }
  printf(" is a great month");

}

Both examples do not use a break statement after each case, which leads to unintended fall-through behavior. For example, calling "printMessage(10)" will result in the text "OctoberNovemberDecember is a great month" being printed.

Example Four

In the excerpt below, an AssertionError (an unchecked exception) is thrown if the user hasn't entered an email address in an HTML form.

String email = request.getParameter("email_address");
assert email != null;

See Also