Exceptions should only be used to denote exceptional conditions. They should not be used for ordinary control flow purposes. Failure to follow this advice complicates both security analysis and debugging, can result in abnormal control flow and can cause performance degradation.

Noncompliant Code Example

This noncompliant code example attempts to concatenate the string elements of the array values, storing the result as the first element.

String values[] = new String[3];
values[0] = "value1";
values[1] = "value2";
values[2] = "value3";
	
int i;
values[1] = null; // gets null value

try {
  i = 0;
  while(true) {	         
    values[0] = values[0].concat(values[i + 1]); // Concatenate and store in values[0]  
    i++;
  }
} catch (ArrayIndexOutOfBoundsException e) {
  i = 0; // Attempts to initialize i to 0
} catch (NullPointerException npe) {
  // Ignores
}

It uses an ArrayIndexOutOfBoundsException to detect the end of the array and reinitialize the value of variable i to 0 in the catch block. However, when some element of the array is null, a NullPointerException results. This exception is caught and ignored, a violation of guideline EXC15-J. Do not catch NullPointerException. Consequently, the variable i fails to be reinitialized.

The purpose of exception handling is to detect and recover from exceptional conditions, rather than to transfer control flow. Further, the exception-based idiom is slower than the standard non-exceptional code. It also prevents optimizations that the JVM would otherwise perform.

Compliant Solution

This compliant solution uses a standard for loop to concatenate the strings.

String values[] = new String[3];
values[0] = "value1";
values[1] = "value2";
values[2] = "value3";

int i;
for (i = 1; i < values.length; i++) {
  values[0] = values[0].concat(values[i]);
}
i = 0; // Initialize i to 0 after operation

Risk Assessment

Use of exceptions for any purpose other than detecting and handling exceptional conditions complicates both security analysis and debugging, and can cause performance degradation.

Automated Detection

TODO

Related Vulnerabilities

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

Bibliography

\[[Bloch 2001|AA. Bibliography#Bloch 01]\] Item 39: "Use exceptions only for exceptional conditions"
\[[JLS 2005|AA. Bibliography#JLS 05]\]

ERR01-J. Use a class dedicated to reporting exceptions      06. Exceptional Behavior (EXC)      ERR03-J. Use a logging API to log critical security exceptions