CWE-333: Improper Handling of Insufficient Entropy in TRNG

What is Improper Handling of Insufficient Entropy in TRNG?

• Overview: Improper Handling of Insufficient Entropy in TRNG (CWE-333) occurs when a true random number generator is used without accounting for its limited entropy source, leading to potential failures or blocking. This vulnerability arises from generating random numbers faster than the entropy can be replenished, which is crucial for security purposes.

• Exploitation Methods:

• Attackers can exploit this vulnerability by predicting random number outputs if the entropy pool is exhausted.
• Common attack patterns include timing attacks to determine when the entropy is low and exploiting the predictability of numbers generated with insufficient entropy.

• Security Impact:

• Direct consequences of successful exploitation include the ability to predict cryptographic keys, session tokens, or other security-critical random values.
• Potential cascading effects involve broader compromise of secure communications, authentication systems, and data integrity.
• Business impact includes loss of sensitive information, reputational damage, and potential legal liabilities.

• Prevention Guidelines:

• Specific code-level fixes include ensuring that random number generation logic accounts for and handles insufficient entropy conditions.
• Security best practices involve using high-quality entropy sources and integrating entropy checks before generating random numbers.
• Recommended tools and frameworks include using established libraries that manage entropy properly, such as those provided by operating systems or cryptographic libraries with TRNG support.

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Technical Details

Likelihood of Exploit: Low

Affected Languages: Not Language-Specific

Affected Technologies: Not specified

Vulnerable Code Example

const crypto = require('crypto');

function generateSecureToken(length) {
    // Vulnerable: Using crypto.randomBytes synchronously without error handling
    // This can lead to poor randomness if entropy is low or the call blocks
    try {
        return crypto.randomBytes(length);  // Potential for blocking without error handling
    } catch (err) {
        console.error('Error generating secure token:', err);
        return null;
    }
}

How to fix Improper Handling of Insufficient Entropy in TRNG?

In JavaScript, especially in Node.js, the crypto module provides methods for cryptographic operations. When using crypto.randomBytes, it is crucial to handle cases where entropy might be insufficient. The asynchronous version of crypto.randomBytes should be used to prevent blocking and handle potential errors.

To fix this:

• Use the asynchronous version of crypto.randomBytes to avoid blocking the event loop.
• Implement error handling to manage situations where entropy is insufficient.

Fixed Code Example

const crypto = require('crypto');

function generateSecureToken(length, callback) {
    // Fixed: Using the async version of crypto.randomBytes to avoid blocking
    // This handles potential errors due to insufficient entropy
    crypto.randomBytes(length, (err, buffer) => {
        if (err) {
            console.error('Error generating secure token due to insufficient entropy:', err);
            callback(err, null);
        } else {
            callback(null, buffer);  // Successfully generated secure token
        }
    });
}

In both examples, proper use of the crypto module and error handling ensures that the code does not block indefinitely and that it gracefully handles situations with low entropy, making the random number generation more robust and secure. The use of asynchronous methods is a best practice in Node.js to prevent blocking operations from hindering application performance.