CWE-374: Passing Mutable Objects to an Untrusted Method

Description

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

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.

Potential Impact

Integrity

Modify Memory

Demonstrative Examples

The following example demonstrates the weakness.

Bad

private:int foo;complexType bar;String baz;otherClass externalClass;
                     
                     public:void doStuff() {externalClass.doOtherStuff(foo, bar, baz)}

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

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

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
                                 sales.updateSalesInformation(book);
                                 // update inventory
                                 inventory.updateInventory(book);
                           }
                           // 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. [REF-374]

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

...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
                           sales.updateSalesInformation(bookSold);
                           // update inventory
                           inventory.updateInventory(book);
                     }...

Mitigations & Prevention

Implementation

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

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.

Taxonomy Mappings

CLASP: — Passing mutable objects to an untrusted method
The CERT Oracle Secure Coding Standard for Java (2011): OBJ04-J — Provide mutable classes with copy functionality to safely allow passing instances to untrusted code
Software Fault Patterns: SFP23 — Exposed Data

Frequently Asked Questions

What is CWE-374?

CWE-374 (Passing Mutable Objects to an Untrusted Method) is a software weakness identified by MITRE's Common Weakness Enumeration. It is classified as a Base-level weakness. The product sends non-cloned mutable data as an argument to a method or function.

How can CWE-374 be exploited?

Attackers can exploit CWE-374 (Passing Mutable Objects to an Untrusted Method) to modify memory. This weakness is typically introduced during the Implementation phase of software development.

How do I prevent CWE-374?

Key mitigations include: Pass in data which should not be altered as constant or immutable.

What is the severity of CWE-374?

CWE-374 is classified as a Base-level weakness (Medium abstraction). Its actual severity depends on the specific context and how the weakness manifests in your application.