Common Weakness Enumeration

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CWE-374: Passing Mutable Objects to an Untrusted Method

Weakness ID: 374
Abstraction: Base
Status: Draft
Presentation Filter:
+ Description

Description Summary

The program sends non-cloned mutable data as an argument to a method or function.

Extended Description

The function or method that has been called can alter or delete the mutable data. This could violate assumptions that the calling function has made about its state. In situations where unknown code is called with references to mutable data, this external code could make changes to the data sent. If this data was not previously cloned, the modified data might not be valid in the context of execution.

+ Time of Introduction
  • Implementation
+ Applicable Platforms






+ Common Consequences

Technical Impact: Modify memory

Potentially data could be tampered with by another function which should not have been tampered with.

+ Likelihood of Exploit


+ Demonstrative Examples

Example 1

(Bad Code)
Example Languages: C and C++ 
int foo;
complexType bar;
String baz;
otherClass externalClass;

void doStuff() {
externalClass.doOtherStuff(foo, bar, baz)

In this example, bar and baz will be passed by reference to doOtherStuff() which may change them.

Example 2

In the following Java example, the BookStore class manages the sale of books in a bookstore, this class includes the member objects for the bookstore inventory and sales database manager classes. The BookStore class includes a method for updating the sales database and inventory when a book is sold. This method retrieves a Book object from the bookstore inventory object using the supplied ISBN number for the book class, then calls a method for the sales object to update the sales information and then calls a method for the inventory object to update inventory for the BookStore.

(Bad Code)
Example Language: Java 
public class BookStore {
private BookStoreInventory inventory;
private SalesDBManager sales;
// constructor for BookStore
public BookStore() {
this.inventory = new BookStoreInventory();
this.sales = new SalesDBManager();
public void updateSalesAndInventoryForBookSold(String bookISBN) {
// Get book object from inventory using ISBN
Book book = inventory.getBookWithISBN(bookISBN);
// update sales information for book sold
// update inventory
// other BookStore methods
public class Book {
private String title;
private String author;
private String isbn;
// Book object constructors and get/set methods

However, in this example the Book object that is retrieved and passed to the method of the sales object could have its contents modified by the method. This could cause unexpected results when the book object is sent to the method for the inventory object to update the inventory.

In the Java programming language arguments to methods are passed by value, however in the case of objects a reference to the object is passed by value to the method. When an object reference is passed as a method argument a copy of the object reference is made within the method and therefore both references point to the same object. This allows the contents of the object to be modified by the method that holds the copy of the object reference. [R.374.1]

In this case the contents of the Book object could be modified by the method of the sales object prior to the call to update the inventory.

To prevent the contents of the Book object from being modified, a copy of the Book object should be made before the method call to the sales object. In the following example a copy of the Book object is made using the clone() method and the copy of the Book object is passed to the method of the sales object. This will prevent any changes being made to the original Book object.

(Good Code)
Example Language: Java 
public void updateSalesAndInventoryForBookSold(String bookISBN) {
// Get book object from inventory using ISBN
Book book = inventory.getBookWithISBN(bookISBN);
// Create copy of book object to make sure contents are not changed
Book bookSold = (Book) book.clone();
// update sales information for book sold
// update inventory
+ Potential Mitigations

Phase: Implementation

Pass in data which should not be altered as constant or immutable.

Phase: Implementation

Clone all mutable data before passing it into an external function . This is the preferred mitigation. This way, regardless of what changes are made to the data, a valid copy is retained for use by the class.

+ Relationships
NatureTypeIDNameView(s) this relationship pertains toView(s)
ChildOfCategoryCategory371State Issues
Development Concepts (primary)699
ChildOfWeakness ClassWeakness Class668Exposure of Resource to Wrong Sphere
Research Concepts (primary)1000
ChildOfCategoryCategory849CERT Java Secure Coding Section 04 - Object Orientation (OBJ)
Weaknesses Addressed by the CERT Java Secure Coding Standard (primary)844
ChildOfCategoryCategory963SFP Secondary Cluster: Exposed Data
Software Fault Pattern (SFP) Clusters (primary)888
+ Taxonomy Mappings
Mapped Taxonomy NameNode IDFitMapped Node Name
CLASPPassing mutable objects to an untrusted method
CERT Java Secure CodingOBJ04-JProvide mutable classes with copy functionality to safely allow passing instances to untrusted code
Software Fault PatternsSFP23Exposed Data
+ References
[R.374.1] Tony Sintes. "Does Java pass by reference or pass by value?". 2000-05-26. <>.
[R.374.2] Herbert Schildt. "Java: The Complete Reference, J2SE 5th Edition".
+ Content History
Submission DateSubmitterOrganizationSource
CLASPExternally Mined
Modification DateModifierOrganizationSource
2008-07-01Eric DalciCigitalExternal
updated Time_of_Introduction
2008-09-08CWE Content TeamMITREInternal
updated Applicable_Platforms, Common_Consequences, Relationships, Other_Notes, Taxonomy_Mappings
2010-06-21CWE Content TeamMITREInternal
updated Name, Taxonomy_Mappings
2010-12-13CWE Content TeamMITREInternal
updated Demonstrative_Examples
2011-06-01CWE Content TeamMITREInternal
updated Common_Consequences, Relationships, Taxonomy_Mappings
2012-05-11CWE Content TeamMITREInternal
updated Relationships, Taxonomy_Mappings
2014-06-23CWE Content TeamMITREInternal
updated Demonstrative_Examples, Description, Other_Notes, Potential_Mitigations, References
2014-07-30CWE Content TeamMITREInternal
updated Relationships, Taxonomy_Mappings
Previous Entry Names
Change DatePrevious Entry Name
2010-06-21Mutable Objects Passed by Reference

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Page Last Updated: May 05, 2017