CWE-568: finalize() Method Without super.finalize()

What is finalize() Method Without super.finalize()?

• Overview: The vulnerability CWE-568 occurs when a Java class implements a finalize() method but fails to call super.finalize(). This oversight can disrupt the proper cleanup of resources and object finalization.

• Exploitation Methods:

• Attackers cannot directly exploit this vulnerability for malicious purposes.
• It can lead to resource leaks or improper resource management, indirectly affecting software performance and reliability.

• Security Impact:

• Direct consequences include resource leaks such as memory or file handles not being properly released.
• Potential cascading effects include system instability, increased memory usage, and application crashes.
• Business impact may involve degraded application performance, increased maintenance costs, and diminished user trust due to unreliability.

• Prevention Guidelines:

• Specific code-level fixes include ensuring that any override of finalize() calls super.finalize() within the method.
• Security best practices involve reviewing finalize() implementations to confirm they adhere to Java specifications.
• Recommended tools and frameworks include static code analysis tools like SonarQube or FindBugs to detect missing super.finalize() calls.

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Technical Details

Likelihood of Exploit: Not specified

Affected Languages: Java

Affected Technologies: Not specified

Vulnerable Code Example

// This class represents a custom resource handler that overrides finalize().
// However, it fails to call super.finalize(), which could lead to resource leaks.
public class ResourceHandler {
    
    // Some resource that needs cleanup
    private FileHandler fileHandler;

    public ResourceHandler() {
        // Initialize resource
        this.fileHandler = new FileHandler("logfile.txt");
    }

    @Override
    protected void finalize() throws Throwable {
        try {
            // Attempt to close the file handler
            if (fileHandler != null) {
                fileHandler.close();
            }
            // Missing call to super.finalize() could prevent superclass cleanup
        } finally {
            // No call to the superclass finalize method, which could prevent proper cleanup
        }
    }
}

How to fix finalize() Method Without super.finalize()?

The finalize() method serves as a safety mechanism to clean up resources that might not have been explicitly released. When overriding finalize() in a subclass, it's crucial to call super.finalize() to ensure the superclass can finalize its resources. Omitting this call can lead to resource leaks and unpredictable behavior, especially if the superclass manages critical resources.

To fix this issue:

1. Always Call super.finalize(): Ensure that super.finalize() is called within your finalize() method. This ensures the superclass's resources are finalized.
2. Use try-finally Blocks Wisely: Place the super.finalize() call within a finally block to ensure it executes even if an exception occurs during resource cleanup.

Fixed Code Example

// This class represents a custom resource handler with proper finalization.
// It correctly calls super.finalize() to ensure superclass resources are managed.
public class ResourceHandler {
    
    // Some resource that needs cleanup
    private FileHandler fileHandler;

    public ResourceHandler() {
        // Initialize resource
        this.fileHandler = new FileHandler("logfile.txt");
    }

    @Override
    protected void finalize() throws Throwable {
        try {
            // Attempt to close the file handler
            if (fileHandler != null) {
                fileHandler.close();
            }
        } finally {
            // Call to super.finalize() ensures superclass resources are finalized
            super.finalize();
        }
    }
}

In the fixed code, we ensure that super.finalize() is called within the finally block. This guarantees that no matter what happens during the cleanup of resources in the finalize() method, the superclass's finalization logic will still execute, preventing potential resource leaks and maintaining consistent program behavior.

Additionally, it's worth noting that starting with Java 9, the use of finalize() is deprecated due to its unpredictability and performance issues. It's recommended to use other resource management techniques like try-with-resources or explicit cleanup methods.