CWE-486: Comparison of Classes by Name

Description

The product compares classes by name, which can cause it to use the wrong class when multiple classes can have the same name.

If the decision to trust the methods and data of an object is based on the name of a class, it is possible for malicious users to send objects of the same name as trusted classes and thereby gain the trust afforded to known classes and types.

Potential Impact

Integrity, Confidentiality, Availability

Execute Unauthorized Code or Commands

Demonstrative Examples

In this example, the expression in the if statement compares the class of the inputClass object to a trusted class by comparing the class names.

Bad

if (inputClass.getClass().getName().equals("TrustedClassName")) {
                        
                           
                           // Do something assuming you trust inputClass
                           
                           
                           // ...
                           
                        
                     }

However, multiple classes can have the same name therefore comparing an object's class by name can allow untrusted classes of the same name as the trusted class to be use to execute unintended or incorrect code. To compare the class of an object to the intended class the getClass() method and the comparison operator "==" should be used to ensure the correct trusted class is used, as shown in the following example.

Good

if (inputClass.getClass() == TrustedClass.class) {
                        
                           
                           // Do something assuming you trust inputClass
                           
                           
                           // ...
                           
                        
                     }

In this example, the Java class, TrustedClass, overrides the equals method of the parent class Object to determine equivalence of objects of the class. The overridden equals method first determines if the object, obj, is the same class as the TrustedClass object and then compares the object's fields to determine if the objects are equivalent.

Bad

public class TrustedClass {
                        ...
                           @Overridepublic boolean equals(Object obj) {
                              boolean isEquals = false;
                                 
                                 // first check to see if the object is of the same class
                                 if (obj.getClass().getName().equals(this.getClass().getName())) {
                                    
                                       
                                       // then compare object fields
                                       ...if (...) {isEquals = true;}
                                 }
                                 return isEquals;
                           }
                           ...
                     }

However, the equals method compares the class names of the object, obj, and the TrustedClass object to determine if they are the same class. As with the previous example using the name of the class to compare the class of objects can lead to the execution of unintended or incorrect code if the object passed to the equals method is of another class with the same name. To compare the class of an object to the intended class, the getClass() method and the comparison operator "==" should be used to ensure the correct trusted class is used, as shown in the following example.

Good

public boolean equals(Object obj) {
                        ...
                           
                           // first check to see if the object is of the same class
                           if (obj.getClass() == this.getClass()) {...}
                           ...
                     }

Mitigations & Prevention

Implementation

Use class equivalency to determine type. Rather than use the class name to determine if an object is of a given type, use the getClass() method, and == operator.

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

7 Pernicious Kingdoms: — Comparing Classes by Name
CLASP: — Comparing classes by name
The CERT Oracle Secure Coding Standard for Java (2011): OBJ09-J — Compare classes and not class names
Software Fault Patterns: SFP1 — Glitch in computation

Frequently Asked Questions

What is CWE-486?

CWE-486 (Comparison of Classes by Name) is a software weakness identified by MITRE's Common Weakness Enumeration. It is classified as a Variant-level weakness. The product compares classes by name, which can cause it to use the wrong class when multiple classes can have the same name.

How can CWE-486 be exploited?

Attackers can exploit CWE-486 (Comparison of Classes by Name) to execute unauthorized code or commands. This weakness is typically introduced during the Implementation phase of software development.

How do I prevent CWE-486?

Key mitigations include: Use class equivalency to determine type. Rather than use the class name to determine if an object is of a given type, use the getClass() method, and == operator.

What is the severity of CWE-486?

CWE-486 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.