CWE-492

Use of Inner Class Containing Sensitive Data
AI Translation Available

Inner classes are translated into classes that are accessible at package scope and may expose code that the programmer intended to keep private to attackers.

Status
draft
Abstraction
variant
Likelihood
medium
Java

Inner classes quietly introduce several security concerns because of the way they are translated into Java bytecode. In Java source code, it appears that an inner class can be declared to be accessible only by the enclosing class, but Java bytecode has no concept of an inner class, so the compiler must transform an inner class declaration into a peer class with package level access to the original outer class. More insidiously, since an inner class can access private fields in its enclosing class, once an inner class becomes a peer class in bytecode, the compiler converts private fields accessed by the inner class into protected fields.

Common Consequences

confidentiality
Impacts
read application data

Detection Methods

automated static analysis

Potential Mitigations

Phases:
implementation
Descriptions:
• 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.
• Using sealed classes protects object-oriented encapsulation paradigms and therefore protects code from being extended in unforeseen ways.