Overview

Omitting a break statement so that one may fall through is often indistinguishable from an error, and therefore should not be used.

Consequences

Unspecified.

Exposure period

• Pre-design through Build: The use of tools to detect this problem is recommended.

• Implementation: Many logic errors can lead to this condition. It can be exacerbated by lack of or misuse of mitigating technologies

Platform

• Languages: C/C++/Java

• Operating platforms: Any

Required resources

Any

Severity

High

Likelihood of exploit

Medium

Avoidance and mitigation

• Pre-design through Build: Most static analysis programs should be able to catch these errors.

• Implementation: The functionality of omitting a break statement could be clarified with an if statement. This method is much safer.

Discussion

While most languages with similar constructs automatically run only a single branch, C and C++ are different. This has bitten many programmers, and can lead to critical code executing in situations where it should not.

Examples

Java:

{    
    int month = 8;
        switch (month) {
            case 1:  print("January");
            case 2:  print("February");
            case 3:  print("March");
            case 4:  print("April");
            case 5:  println("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");
  }

C/C++:

Is identical if one replaces print with printf or cout.

One might think that if they just tested case12, it will display that the respective month "is a great month." However, if one tested November, one notice that it would display "November December is a great month."