Returning a Mutable Object to an Untrusted Caller

Sending non-cloned mutable data as a return value may result in that data being altered or deleted by the calling function.


In situations where functions return references to mutable data, it is possible that the external code which called the function may make changes to the data sent. If this data was not previously cloned, the class will then be using modified data which may violate assumptions about its internal state.


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

This class has a private list of patients, but provides a way to see the list :

public class ClinicalTrial {
  private PatientClass[] patientList = new PatientClass[50];
  public getPatients(...){
    return patientList;

While this code only means to allow reading of the patient list, the getPatients() method returns a reference to the class's original patient list instead of a reference to a copy of the list. Any caller of this method can arbitrarily modify the contents of the patient list even though it is a private member of the class.

See Also

Comprehensive Categorization: Exposed Resource

Weaknesses in this category are related to exposed resource.

SEI CERT Perl Coding Standard - Guidelines 03. Expressions (EXP)

Weaknesses in this category are related to the rules and recommendations in the Expressions (EXP) section of the SEI CERT Perl Coding Standard.

SEI CERT Oracle Secure Coding Standard for Java - Guidelines 05. Object Orientation (OBJ)

Weaknesses in this category are related to the rules and recommendations in the Object Orientation (OBJ) section of the SEI CERT Oracle Secure Coding Standard for Java.

Comprehensive CWE Dictionary

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

Weaknesses Introduced During Implementation

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

Weakness Base Elements

This view (slice) displays only weakness base elements.

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