CWE-595: Comparison of Object References Instead of Object Contents

Description

The product compares object references instead of the contents of the objects themselves, preventing it from detecting equivalent objects.

For example, in Java, comparing objects using == usually produces deceptive results, since the == operator compares object references rather than values; often, this means that using == for strings is actually comparing the strings' references, not their values.

Potential Impact

Other

Varies by Context

Demonstrative Examples

In the example below, two Java String objects are declared and initialized with the same string values. An if statement is used to determine if the strings are equivalent.

Bad

String str1 = new String("Hello");String str2 = new String("Hello");if (str1 == str2) {System.out.println("str1 == str2");}

However, the if statement will not be executed as the strings are compared using the "==" operator. For Java objects, such as String objects, the "==" operator compares object references, not object values. While the two String objects above contain the same string values, they refer to different object references, so the System.out.println statement will not be executed. To compare object values, the previous code could be modified to use the equals method:

Good

if (str1.equals(str2)) {System.out.println("str1 equals str2");}

In the following Java example, two BankAccount objects are compared in the isSameAccount method using the == operator.

Bad

public boolean isSameAccount(BankAccount accountA, BankAccount accountB) {return accountA == accountB;}

Using the == operator to compare objects may produce incorrect or deceptive results by comparing object references rather than values. The equals() method should be used to ensure correct results or objects should contain a member variable that uniquely identifies the object.

The following example shows the use of the equals() method to compare the BankAccount objects and the next example uses a class get method to retrieve the bank account number that uniquely identifies the BankAccount object to compare the objects.

Good

public boolean isSameAccount(BankAccount accountA, BankAccount accountB) {return accountA.equals(accountB);}

Mitigations & Prevention

Implementation

In Java, use the equals() method to compare objects instead of the == operator. If using ==, it is important for performance reasons that your objects are created by a static factory, not by a constructor.

Detection Methods

Automated Static Analysis High — Automated static analysis, commonly referred to as Static Application Security Testing (SAST), can find some instances of this weakness by analyzing source code (or binary/compiled code) without having to execute it. Typically, this is done by building a model of data flow and control flow, then sea

Taxonomy Mappings

The CERT Oracle Secure Coding Standard for Java (2011): EXP02-J — Use the two-argument Arrays.equals() method to compare the contents of arrays
The CERT Oracle Secure Coding Standard for Java (2011): EXP02-J — Use the two-argument Arrays.equals() method to compare the contents of arrays
The CERT Oracle Secure Coding Standard for Java (2011): EXP03-J — Do not use the equality operators when comparing values of boxed primitives

Frequently Asked Questions

What is CWE-595?

CWE-595 (Comparison of Object References Instead of Object Contents) is a software weakness identified by MITRE's Common Weakness Enumeration. It is classified as a Variant-level weakness. The product compares object references instead of the contents of the objects themselves, preventing it from detecting equivalent objects.

How can CWE-595 be exploited?

Attackers can exploit CWE-595 (Comparison of Object References Instead of Object Contents) to varies by context. This weakness is typically introduced during the Implementation phase of software development.

How do I prevent CWE-595?

Key mitigations include: In Java, use the equals() method to compare objects instead of the == operator. If using ==, it is important for performance reasons that your objects are created by a static factory, not by a constru

What is the severity of CWE-595?

CWE-595 is classified as a Variant-level weakness (Low-Medium abstraction). Its actual severity depends on the specific context and how the weakness manifests in your application.