CWE-670: Always-Incorrect Control Flow Implementation

Description

The code contains a control flow path that does not reflect the algorithm that the path is intended to implement, leading to incorrect behavior any time this path is navigated.

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.

Potential Impact

Other

Other, Alter Execution Logic

Demonstrative Examples

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

Bad

$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).

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.

Bad

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.

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

Bad

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");
               }

Bad

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.

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

Bad

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

Real-World CVE Examples

CVE ID	Description
CVE-2021-3011	virtual interrupt controller in a virtualization product allows crash of host by writing a certain invalid value to a register, which triggers a fatal error instead of returning an error code

Frequently Asked Questions

What is CWE-670?

CWE-670 (Always-Incorrect Control Flow Implementation) is a software weakness identified by MITRE's Common Weakness Enumeration. It is classified as a Class-level weakness. The code contains a control flow path that does not reflect the algorithm that the path is intended to implement, leading to incorrect behavior any time this path is navigated.

How can CWE-670 be exploited?

Attackers can exploit CWE-670 (Always-Incorrect Control Flow Implementation) to other, alter execution logic. This weakness is typically introduced during the Implementation phase of software development.

How do I prevent CWE-670?

Follow secure coding practices, conduct code reviews, and use automated security testing tools (SAST/DAST) to detect this weakness early in the development lifecycle.

What is the severity of CWE-670?

CWE-670 is classified as a Class-level weakness (High abstraction). It has been observed in 1 real-world CVEs.