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 searching for potentially-vulnerable patterns that connect "sources" (origins of input) with "sinks" (destinations where the data interacts with external components, a lower layer such as the OS, etc.)
CWE-595 Variant Incomplete
Comparison of Object References Instead of Object Contents
This vulnerability occurs when code incorrectly checks if two object references point to the same memory location, rather than comparing the actual data or values contained within the objects. This…
Definition
What is CWE-595?
This vulnerability occurs when code incorrectly checks if two object references point to the same memory location, rather than comparing the actual data or values contained within the objects. This mistake prevents the software from correctly identifying when two separate objects hold equivalent content.
In many programming languages, the default comparison operator (like `==` in Java or `is` in Python) checks for *reference equality*. This means it only returns true if both variables point to the exact same object in memory. To properly compare the internal state or data of two objects, you must use a method designed for *value equality*, such as `.equals()` in Java, `.equals()` or value comparators in C#, or overriding the `==` operator in languages that support it.
This is a common pitfall, especially with strings and collections. For instance, using `==` on two Java `String` objects with the same text will often fail because they are distinct objects in memory. Developers must be intentional about their comparison logic, choosing the correct method based on whether they need to verify object identity or object content, as using the wrong check leads to flawed program logic and unexpected behavior.
Real-world impact
Real-world CVEs caused by CWE-595
No public CVE references are linked to this CWE in MITRE's catalog yet.
How attackers exploit it
Step-by-step attacker path
- 1
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.
- 2
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:
- 3
In the following Java example, two BankAccount objects are compared in the isSameAccount method using the == operator.
- 4
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.
- 5
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.
Vulnerable code example
Vulnerable Java
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.
String str1 = new String("Hello");
String str2 = new String("Hello");
if (str1 == str2) {
System.out.println("str1 == str2");
} Secure code example
Secure Java
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:
if (str1.equals(str2)) {
System.out.println("str1 equals str2");
} What changed: the unsafe sink is replaced (or the input is validated/escaped) so the same payload no longer triggers the weakness.
Prevention checklist
How to prevent CWE-595
- 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 signals
How to detect CWE-595
CWE-595
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Frequently asked questions What is CWE-595?
How serious is CWE-595?
What languages or platforms are affected by CWE-595?
How can I prevent CWE-595?
How does Plexicus detect and fix CWE-595?
Where can I learn more about CWE-595?
Frequently asked questions
What is CWE-595?
This vulnerability occurs when code incorrectly checks if two object references point to the same memory location, rather than comparing the actual data or values contained within the objects. This mistake prevents the software from correctly identifying when two separate objects hold equivalent content.
How serious is CWE-595?
MITRE has not published a likelihood-of-exploit rating for this weakness. Treat it as medium-impact until your threat model proves otherwise.
What languages or platforms are affected by CWE-595?
MITRE lists the following affected platforms: Java, JavaScript, PHP.
How can I prevent CWE-595?
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.
How does Plexicus detect and fix CWE-595?
Plexicus's SAST engine matches the data-flow signature for CWE-595 on every commit. When a match is found, our Codex Remedium agent opens a fix PR with the corrected code, tests, and a one-line summary for the reviewer.
Where can I learn more about CWE-595?
MITRE publishes the canonical definition at https://cwe.mitre.org/data/definitions/595.html. You can also reference OWASP and NIST documentation for adjacent guidance.
Related weaknesses
Weaknesses related to CWE-595
CWE-1025 Parent
Comparison Using Wrong Factors
This weakness occurs when a program compares two items but checks the wrong properties or attributes. This flawed comparison leads to…
CWE-486 Sibling
Comparison of Classes by Name
This vulnerability occurs when an application determines an object's trustworthiness or behavior solely by checking its class name. Since…
CWE-1097 Child
Persistent Storable Data Element without Associated Comparison Control Element
This weakness occurs when a persistent data object lacks the necessary methods to be properly compared, which can lead to inconsistent or…
CWE-597 Child
Use of Wrong Operator in String Comparison
This vulnerability occurs when a developer incorrectly compares string values, typically by using reference equality operators (like == or…
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