If a function is implicitly declared and it is not given enough arguments it will still pop the expected number from the stack. This could cause the program to crash.

Non compliant code

function(1, 2);
...
void function(int one, int two, int three){
printf("args %d %d $d, one, two, three);
}

Solution: Use function prototypes at the top of .c file or in a .h file so that a compiler error will occur if an incorrect number of arguments are used.

Compliant code

void function(int one, int two, int three); //at top of file or in .h file
...
function(1,2) //compiler error

Also using a compiler setting that checks for implicity declared function will prevent accidentally calling a function before it is declared.

gcc 3.4.6 for example will not allow the non compliant code above. 

Risk Assesment

References

• http://cwe.mitre.org/