CWE-492 Variant Draft 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,…

Definition

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.

Auswirkungen in der Praxis

Real-world CVEs caused by CWE-492

Bisher sind in MITREs Katalog keine öffentlichen CVE-Referenzen mit dieser CWE verknüpft.

Wie Angreifer es ausnutzen

Angreiferpfad Schritt für Schritt

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.

Verwundbares Codebeispiel

Vulnerable Java

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

Verwundbar Java

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

Sicheres Codebeispiel

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.

Sicher 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.

Präventions-Checkliste

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.

Erkennungssignale

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.)

Plexicus Auto-Fix

Plexicus erkennt CWE-492 automatisch und öffnet in unter 60 Sekunden einen Fix-PR.

Codex Remedium scannt jeden Commit, identifiziert genau diese Schwachstelle und liefert einen reviewer-ready Pull Request mit dem Patch. Keine Tickets. Keine Hand-offs.

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Häufig gestellte Fragen

Frequently asked questions

Was ist CWE-492?

Wie gravierend ist CWE-492?

MITRE stuft die Exploit-Wahrscheinlichkeit als mittel ein — eine Ausnutzung ist realistisch, erfordert aber meist bestimmte Bedingungen.

Welche Sprachen oder Plattformen sind von CWE-492 betroffen?

MITRE lists the following affected platforms: Java.

Wie kann ich CWE-492 verhindern?

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.

Wie erkennt und behebt Plexicus CWE-492?

Die SAST-Engine von Plexicus erkennt die Datenfluss-Signatur von CWE-492 bei jedem Commit. Bei einem Treffer öffnet unser Codex-Remedium-Agent einen Fix-PR mit korrigiertem Code, Tests und einer einzeiligen Zusammenfassung für den Reviewer.

Wo erfahre ich mehr über CWE-492?

MITRE veröffentlicht die kanonische Definition unter https://cwe.mitre.org/data/definitions/492.html. Für ergänzende Hinweise kannst du auch die OWASP- und NIST-Dokumentation heranziehen.

Verwandte Schwachstellen

Weaknesses related to CWE-492

CWE-668 Parent

Exposure of Resource to Wrong Sphere

This vulnerability occurs when an application unintentionally makes a resource accessible to users or systems that should not have…

CWE-1189 Sibling

Improper Isolation of Shared Resources on System-on-a-Chip (SoC)

This vulnerability occurs when a System-on-a-Chip (SoC) fails to properly separate shared hardware resources between secure (trusted) and…

CWE-1282 Sibling

Assumed-Immutable Data is Stored in Writable Memory

This vulnerability occurs when data that should be permanent and unchangeable—like a bootloader, device IDs, or one-time configuration…

CWE-1327 Sibling

Binding to an Unrestricted IP Address

This vulnerability occurs when software or a service is configured to bind to the IP address 0.0.0.0 (or :: in IPv6), which acts as a…

CWE-1331 Sibling

Improper Isolation of Shared Resources in Network On Chip (NoC)

This vulnerability occurs when a Network on Chip (NoC) fails to properly separate its internal, shared resources—like buffers, switches,…

CWE-134 Sibling

Use of Externally-Controlled Format String

This vulnerability occurs when a program uses a format string from an untrusted, external source (like user input, a network packet, or a…

CWE-200 Sibling

Exposure of Sensitive Information to an Unauthorized Actor

This weakness occurs when an application unintentionally reveals sensitive data to someone who shouldn't have access to it.

CWE-374 Sibling

Passing Mutable Objects to an Untrusted Method

This vulnerability occurs when a function receives a direct reference to mutable data, such as an object or array, instead of a safe copy…

CWE-375 Sibling

Returning a Mutable Object to an Untrusted Caller

This vulnerability occurs when a method directly returns a reference to its internal mutable data, allowing untrusted calling code to…

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