CWE-304: Missing Critical Step in Authentication

What is Missing Critical Step in Authentication?

• Overview: This vulnerability occurs when an authentication process is not fully implemented, missing a critical step that compromises its effectiveness. It results in a weaker authentication process that can be bypassed or more easily attacked.

• Exploitation Methods:

• Attackers can exploit this vulnerability by identifying the missing step and bypassing the authentication process entirely.
• Common attack patterns include replay attacks, session hijacking, and brute force attacks that take advantage of the incomplete authentication process.

• Security Impact:

• Direct consequences include unauthorized access to systems and data.
• Potential cascading effects involve data breaches, loss of sensitive information, and further exploitation of compromised systems.
• Business impact may include reputational damage, financial losses, and legal implications due to non-compliance with security regulations.

• Prevention Guidelines:

• Specific code-level fixes involve ensuring that all steps of an authentication algorithm are correctly implemented and validated.
• Security best practices include using well-established authentication protocols and regularly reviewing authentication processes for completeness.
• Recommended tools and frameworks include automated security testing tools that can detect missing steps in authentication processes and secure development frameworks that provide proper authentication mechanisms.

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Technical Details

Likelihood of Exploit: Not specified

Affected Languages: Not Language-Specific

Affected Technologies: Not specified

Vulnerable Code Example

```python auth.py {1-11}
import hashlib

def authenticate_user(username, password):
    # Step 1: Retrieve the stored password hash for the user
    stored_password_hash = get_stored_password_hash(username)
    
    # Step 2: Hash the provided password and compare
    # VULNERABLE: Missing a critical step to verify that the user exists before hashing
    provided_password_hash = hashlib.sha256(password.encode()).hexdigest()
    
    # Step 3: Compare the hashes
    if provided_password_hash == stored_password_hash:
        return True
    return False

Explanation:

• The code above skips a critical step in the authentication process: verifying that the user exists before hashing the provided password.
• If a username does not exist in the system, get_stored_password_hash(username) might return None or a default value. Hashing the input without checking for the user first could lead to incorrect behavior or even exploitation through timing attacks.

How to fix Missing Critical Step in Authentication?

To fix this vulnerability, ensure the existence of the user is confirmed before proceeding with password hashing. By doing so, you prevent unnecessary computation and reduce the risk of timing attacks. Implement the following best practices:

1. Verify User Existence: Before hashing the password, check if the user exists in the database.
2. Separate Authentication Steps: Use separate logic for verifying user existence and password matching to ensure clarity and security.
3. Use Secure Password Hashing: Consider using libraries like bcrypt or argon2 for more secure password hashing.

Fixed Code Example

import bcrypt

def authenticate_user(username, password):
    # Step 1: Verify that the user exists
    stored_password_hash = get_stored_password_hash(username)
    if stored_password_hash is None:
        # User does not exist
        return False
    
    # Step 2: Hash the provided password and compare using a secure hashing algorithm
    provided_password_hash = bcrypt.hashpw(password.encode(), stored_password_hash)
    
    # Step 3: Compare the hashes
    if bcrypt.checkpw(password.encode(), stored_password_hash):
        return True
    return False

Explanation:

• Line 6: Added a check to ensure the stored_password_hash is not None, confirming the user exists before proceeding with the hashing process.
• Line 10: Utilized bcrypt for hashing the password, which is a more secure approach compared to hashlib.sha256.
• Line 12: Used bcrypt.checkpw to securely compare the provided password with the stored hash.
• This change ensures that the application follows a correct authentication sequence, preventing potential security loopholes due to missing critical authentication steps.