CWE-343: Predictable Value Range from Previous Values

What is Predictable Value Range from Previous Values?

• Overview: Predictable Value Range from Previous Values refers to a vulnerability where the sequence of values produced by a random number generator can be predicted. When previous values are observed, it becomes possible to infer a limited range for the next potential value, making the sequence less random and more predictable.

• Exploitation Methods:

• Attackers can exploit this vulnerability by observing a series of random numbers and using statistical analysis to predict future values.
• Common attack patterns include brute force attacks that become more efficient due to the reduced number of possibilities to test, based on prior observed values.

• Security Impact:

• Direct consequences include reduced randomness in processes relying on the random number generator, such as encryption keys or session identifiers, leading to weakened security.
• Potential cascading effects may include compromised confidentiality and integrity of sensitive data protected by the affected random values.
• Business impact can involve financial loss, reputational damage, and potential non-compliance with security standards or regulations.

• Prevention Guidelines:

• Specific code-level fixes include using cryptographically secure random number generators that are designed to produce non-predictable sequences.
• Security best practices involve regularly updating and auditing random number generation mechanisms to ensure they meet current security standards.
• Recommended tools and frameworks include libraries and APIs that provide secure random number generation capabilities, such as those found in modern cryptographic libraries.

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Technical Details

Likelihood of Exploit: Not specified

Affected Languages: Not Language-Specific

Affected Technologies: Not specified

Vulnerable Code Example

Certainly! Below is the improved content with the necessary corrections and enhancements:

function generateToken() {
    // Vulnerable: Math.random() is not suitable for cryptographic purposes
    // The values generated are predictable and not secure for sensitive operations
    return Math.floor(Math.random() * 1000000);
}

// Usage
console.log(generateToken());

How to fix Predictable Value Range from Previous Values?

In JavaScript, the Math.random() function is not suitable for generating random numbers for security-critical applications because it does not produce cryptographically secure random numbers. An attacker can potentially predict the sequence of numbers generated by this method.

To fix this issue, use the crypto module available in Node.js, which provides functions to generate cryptographically secure random numbers.

Fixed Code Example

const crypto = require('crypto');

function generateSecureToken() {
    // Fix: Uses crypto.randomInt() to generate a secure random token
    // crypto.randomInt() is designed for cryptographic use and provides secure random numbers
    return crypto.randomInt(0, 1000000);  // Generates a secure random integer between 0 and 999999
}

// Usage
console.log(generateSecureToken());

Explanation

• Vulnerable Code: The use of Math.random() in the vulnerable example is problematic because it produces predictable sequences of numbers, which can be exploited in security-critical applications such as token generation.

• Fixed Code: The fixed example utilizes crypto.randomInt(), which is part of Node.js's crypto module. This method generates cryptographically secure random integers, making it suitable for generating tokens that need to be unpredictable and secure against attacks.

This change ensures that the values generated for tokens are not predictable, mitigating the risk associated with CWE-343.