CWE-492 Variante Brouillon Medium likelihood

Use of Inner Class Containing Sensitive Data

Using inner classes to handle sensitive data can unintentionally expose that data because of how Java compiles them. The compiler transforms inner classes into separate, package-visible classes,…

Définition

What is CWE-492?

Using inner classes to handle sensitive data can unintentionally expose that data because of how Java compiles them. The compiler transforms inner classes into separate, package-visible classes, which can bypass the intended private access restrictions.

Inner classes in Java create hidden security risks due to their compilation process. While your source code might declare an inner class as private to its enclosing class, the Java bytecode has no built-in support for this relationship. To make it work, the compiler converts the inner class into a separate peer class with package-level access. This means code you intended to keep private within a single class becomes accessible to all other classes in the same package. This becomes especially dangerous because inner classes can access private fields of their outer class. To allow this access in the transformed bytecode, the compiler silently changes those private fields to protected scope. As a result, sensitive data you marked as private can be exposed through the newly created peer class, breaking your intended encapsulation and creating a potential data leak.

Impact réel

Real-world CVEs caused by CWE-492

Aucune référence CVE publique n'est liée à ce CWE dans le catalogue MITRE pour le moment.

Comment les attaquants l'exploitent

Parcours de l'attaquant étape par étape

1
The following Java Applet code mistakenly makes use of an inner class.
2
The following example shows a basic use of inner classes. The class OuterClass contains the private member inner class InnerClass. The private inner class InnerClass includes the method concat that accesses the private member variables of the class OuterClass to output the value of one of the private member variables of the class OuterClass and returns a string that is a concatenation of one of the private member variables of the class OuterClass, the separator input parameter of the method and the private member variable of the class InnerClass.
3
Although this is an acceptable use of inner classes it demonstrates one of the weaknesses of inner classes that inner classes have complete access to all member variables and methods of the enclosing class even those that are declared private and protected. When inner classes are compiled and translated into Java bytecode the JVM treats the inner class as a peer class with package level access to the enclosing class.
4
To avoid this weakness of inner classes, consider using either static inner classes, local inner classes, or anonymous inner classes.
5
The following Java example demonstrates the use of static inner classes using the previous example. The inner class InnerClass is declared using the static modifier that signifies that InnerClass is a static member of the enclosing class OuterClass. By declaring an inner class as a static member of the enclosing class, the inner class can only access other static members and methods of the enclosing class and prevents the inner class from accessing nonstatic member variables and methods of the enclosing class. In this case the inner class InnerClass can only access the static member variable memberTwo of the enclosing class OuterClass but cannot access the nonstatic member variable memberOne.

Exemple de code vulnérable

Vulnerable Java

The following Java Applet code mistakenly makes use of an inner class.

Vulnérable Java

public final class urlTool extends Applet {
  	private final class urlHelper {
  		...
  	}
  	...
  }

Exemple de code sécurisé

Secure Java

The following Java example demonstrates the use of static inner classes using the previous example. The inner class InnerClass is declared using the static modifier that signifies that InnerClass is a static member of the enclosing class OuterClass. By declaring an inner class as a static member of the enclosing class, the inner class can only access other static members and methods of the enclosing class and prevents the inner class from accessing nonstatic member variables and methods of the enclosing class. In this case the inner class InnerClass can only access the static member variable memberTwo of the enclosing class OuterClass but cannot access the nonstatic member variable memberOne.

Sécurisé Java

public class OuterClass {
```
// private member variables of OuterClass* 
  		private String memberOne;
  		private static String memberTwo;
  		
  		
  		 *// constructor of OuterClass* 
  		public OuterClass(String varOne, String varTwo) {
  		
  		```
  			this.memberOne = varOne;
  			this.memberTwo = varTwo;
  		}
```
// InnerClass is a static inner class of OuterClass* 
  		private static class InnerClass {
  		```
  				private String innerMemberOne;
  				public InnerClass(String innerVarOne) {
  					this.innerMemberOne = innerVarOne;
  				}
  				public String concat(String separator) {
```
// InnerClass only has access to static member variables of OuterClass* 
  						return memberTwo + separator + this.innerMemberOne;}}}

What changed: the unsafe sink is replaced (or the input is validated/escaped) so the same payload no longer triggers the weakness.

Liste de contrôle de prévention

How to prevent CWE-492

Implementation Using sealed classes protects object-oriented encapsulation paradigms and therefore protects code from being extended in unforeseen ways.
Implementation Inner Classes do not provide security. Warning: Never reduce the security of the object from an outer class, going to an inner class. If an outer class is final or private, ensure that its inner class is private as well.

Signaux de détection

How to detect CWE-492

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 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.)

Correction automatique Plexicus

Plexicus détecte automatiquement CWE-492 et ouvre une PR de correction en moins de 60 secondes.

Codex Remedium analyse chaque commit, identifie cette faiblesse précise et livre une pull request prête à être relue avec le correctif. Pas de tickets. Pas de transferts.

Obtenir une démo Essayer Plexicus gratuitement

Questions fréquentes

Frequently asked questions

Qu'est-ce que CWE-492 ?

Quelle est la gravité de CWE-492 ?

MITRE évalue la probabilité d'exploitation comme Moyenne — l'exploitation est réaliste mais nécessite généralement des conditions spécifiques.

Quels langages ou plateformes sont affectés par CWE-492 ?

MITRE lists the following affected platforms: Java.

Comment puis-je prévenir CWE-492 ?

Using sealed classes protects object-oriented encapsulation paradigms and therefore protects code from being extended in unforeseen ways. Inner Classes do not provide security. Warning: Never reduce the security of the object from an outer class, going to an inner class. If an outer class is final or private, ensure that its inner class is private as well.

Comment Plexicus détecte et corrige CWE-492 ?

Le moteur SAST de Plexicus reconnaît la signature de flux de données de CWE-492 à chaque commit. Lorsqu'une correspondance est trouvée, notre agent Codex Remedium ouvre une PR de correction avec le code corrigé, les tests et un résumé d'une ligne pour le relecteur.

Où puis-je en savoir plus sur CWE-492 ?

MITRE publie la définition canonique à https://cwe.mitre.org/data/definitions/492.html. Vous pouvez également consulter la documentation OWASP et NIST pour des conseils adjacents.

Faiblesses associées

Weaknesses related to CWE-492

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