CWE-334: Small Space of Random Values

What is Small Space of Random Values?

• Overview: The CWE-334 vulnerability occurs when the range of possible random values is too small, making it easier for attackers to predict or guess these values through brute-force methods. This often happens when random number generators are not used correctly, resulting in insufficient randomness.

• Exploitation Methods:

• Attackers can exploit this vulnerability by systematically trying all possible values in the small random space until the correct value is found.
• Common attack patterns include brute-force guessing and enumeration of possible values, especially in scenarios like session IDs, tokens, or cryptographic keys.

• Security Impact:

• Direct consequences of successful exploitation include unauthorized access to systems or data, as attackers can predict or replicate values intended to be secret.
• Potential cascading effects include the compromise of additional systems or data protected by the same weak random values.
• Business impact can be significant, including data breaches, loss of customer trust, legal penalties, and financial losses.

• Prevention Guidelines:

• Specific code-level fixes include using cryptographically secure random number generators that provide a sufficiently large space of values.
• Security best practices involve regularly reviewing and testing the randomness of values used in security-critical areas, such as authentication and encryption.
• Recommended tools and frameworks include those that offer built-in support for secure random number generation, such as cryptographic libraries and APIs provided by trusted vendors.

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Technical Details

Likelihood of Exploit: Not specified

Affected Languages: Not Language-Specific

Affected Technologies: Not specified

Vulnerable Code Example

# Vulnerable code: Using random.randint() with a small range for token generation.
# The small range of random values makes the tokens predictable and prone to brute force attacks.

import random

def generate_token():
    token = random.randint(0, 999)  # Generates a token between 0 and 999
    return str(token)

print("Generated token:", generate_token())

Explanation:

• Issue: The use of random.randint(0, 999) generates a token within a very limited range (only 1000 possible values). This makes the tokens highly predictable and susceptible to brute force attacks, as an attacker could easily iterate through all possible values.
• Impact: An attacker could potentially guess a valid token within a short period, compromising security.

How to fix Small Space of Random Values?

To fix this vulnerability, replace the use of random.randint() with functions from the secrets module, which are specifically designed to generate cryptographically secure random numbers. The secrets module provides functions like secrets.token_hex() that generate secure random tokens with a much larger space of random values, making them resistant to attacks.

Fixed Code Example

# Fixed code: Using the secrets module to generate a secure random token.
# secrets.token_hex() generates a secure token with a larger space of random values.

import secrets

def generate_secure_token():
    token = secrets.token_hex(16)  # Generates a secure 32-character hexadecimal token
    return token

print("Generated secure token:", generate_secure_token())

Explanation:

• Solution: The secrets.token_hex(16) function is used to generate a 32-character hexadecimal token. This provides a much larger space of possible values, significantly increasing the difficulty for an attacker to predict or brute-force the token.
• Benefits: By using cryptographically secure methods, the tokens are far more resistant to attacks, enhancing the overall security of the system.

In both examples, the key change involves switching from non-secure random number generation methods, which have a limited range, to cryptographically secure functions that provide a much larger and more unpredictable space of random values, thereby significantly enhancing security against brute force attacks.