EXC32-J. Do not catch RuntimeException

It is highly unlikely that a method is built to deal with all possible runtime exceptions; therefore no method should ever catch RuntimeException. If a method catches RuntimeException, it will receive exceptions it was not designed to handle, such as NullPointerException. Many catch clauses simply log or ignore their error, and resume control flow. But runtime exceptions represent a bug in the program that should be fixed by the developer, and almost always lead to control flow vulnerabilities.

Likewise, a method should never catch Exception or Throwable, since this implies catching RuntimeException.

Noncompliant Code Example

The following function takes a string and returns true if it consists of a capital letter succeeded by lowercase letters. To handle corner cases, it merely wraps the code in a try/catch block and reports any excepts that arise.

boolean isCapitalized(String s) {
  try {
    if (s.equals("")) {
      return true;
    }
    String first = s.substring( 0, 1);
    String rest = s.substring( 1);
    return (first.equals( first.toUpperCase()) &&
	    rest.equals( rest.toLowerCase()));
  } catch (RuntimeException exception) {
    ExceptionReporter.report( exception);
  }
  return false;
}

This code will report errors such as if s is a null pointer, or is the empty string. However, it will also catch other errors unlikely to be handled properly, such as if the string belongs to a different thread.

Compliant Solution

Intead of catching RuntimeException, a program should catch very specific exceptions.

boolean isCapitalized(String s) {
  try {
    if (s.equals("")) {
      return true;
    }
    String first = s.substring( 0, 1);
    String rest = s.substring( 1);
    return (first.equals( first.toUpperCase()) &&
	    rest.equals( rest.toLowerCase()));
  } catch (NullPointerException exception) {
    ExceptionReporter.report( exception);
  }
  return false;
}

This code will only catch exceptions intended by the programmer to be caught. A concurrency-based exception will not be caught by this code, and can therefore be managed by code more specifically designed to handle it.

Exceptions

EXC32-J-EX1: A secure application must also abide by EXC01-J. Do not allow exceptions to transmit sensitive information. In order to follow this rule, an application might find it necessary to catch all exceptions at some 'top' level in order to sanitize (or suppress) them. This is also summarized in the CWE entries, CWE 7 and CWE 388.

Risk Assessment

Catching RuntimeException will trap several types of exceptions not intended to be caught. This prevents them from being handled properly.

Automated Detection

TODO

Related Vulnerabilities

Search for vulnerabilities resulting from the violation of this rule on the CERT website.

References

[[MITRE 09]] CWE ID 396 "Declaration of Catch for Generic Exception", CWE ID 7 "J2EE Misconfiguration: Missing Error Handling"

EXC03-J. Try to recover gracefully from system errors      10. Exceptional Behavior (EXC)      EXC30-J. Do not exit abruptly from a finally block