Private Data Structure Returned From A Public Method

The product has a method that is declared public, but returns a reference to a private data structure, which could then be modified in unexpected ways.


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

SFP Secondary Cluster: Exposed Data

This category identifies Software Fault Patterns (SFPs) within the Exposed Data cluster (SFP23).

7PK - Encapsulation

This category represents one of the phyla in the Seven Pernicious Kingdoms vulnerability classification. It includes weaknesses that occur when the product does not su...

Comprehensive CWE Dictionary

This view (slice) covers all the elements in CWE.

CWE Cross-section

This view contains a selection of weaknesses that represent the variety of weaknesses that are captured in CWE, at a level of abstraction that is likely to be useful t...

Weaknesses Introduced During Implementation

This view (slice) lists weaknesses that can be introduced during implementation.


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