An object reference value from a call to a function that might return null might be dereferenced either explicitly or through a call to a function that can dereference it, without checking for null.

Vulnerability and risk

Dereferencing a null object reference is a critical runtime problem that will crash the application on some operating systems and throw a runtime exception on others.

Example 1

    class Program
        public Program foo()
            if (flag)
                return null;
            return new Program();

        public void var(bool b)
            Program a = foo();
            if (b)
        private bool flag;

Klocwork produces an issue report (CS.NRE.FUNC.MIGHT) at line 18 for variable 'a'. If Variable 'a' is assigned to a value which might be null and which comes from a call to function 'foo' at line 16, it may still be null when it is dereferenced at line 18.

Security training

Application security training materials provided by Secure Code Warrior.