Failure to Handle Missing Parameter

Demonstrations

The following examples help to illustrate the nature of this weakness and describe methods or techniques which can be used to mitigate the risk.

Note that the examples here are by no means exhaustive and any given weakness may have many subtle varieties, each of which may require different detection methods or runtime controls.

Example One

The following example demonstrates the weakness.

foo_funct(one, two);

void foo_funct(int one, int two, int three) {
  printf("1) %d\n2) %d\n3) %d\n", one, two, three);
}

void some_function(int foo, ...) {
  int a[3], i;
  va_list ap;
  va_start(ap, foo);
  for (i = 0; i < sizeof(a) / sizeof(int); i++) a[i] = va_arg(ap, int);
  va_end(ap);
}

int main(int argc, char *argv[]) {
  some_function(17, 42);
}

This can be exploited to disclose information with no work whatsoever. In fact, each time this function is run, it will print out the next 4 bytes on the stack after the two numbers sent to it.

See Also