Private Data Structure Returned From A Public Method

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

Here, a public method in a Java class returns a reference to a private array. Given that arrays in Java are mutable, any modifications made to the returned reference would be reflected in the original private array.

private String[] colors;
public String[] getColors() {
  return colors;
}

Example Two

In this example, the Color class defines functions that return non-const references to private members (an array type and an integer type), which are then arbitrarily altered from outside the control of the class.

class Color
{
  private:
    int[2] colorArray;
    int colorValue;
  public:
    Color () : colorArray { 1, 2 }, colorValue (3) { };
    int[2] & fa () { return colorArray; }    // return reference to private array
    int & fv () { return colorValue; }    // return reference to private integer

};

int main ()
{
  Color c;

  c.fa () [1] = 42;  // modifies private array element
  c.fv () = 42;  // modifies private int

  return 0;
}

See Also