CWE-305: Authentication Bypass by Primary Weakness

What is Authentication Bypass by Primary Weakness?

• Overview: Authentication Bypass by Primary Weakness occurs when the authentication algorithm itself is secure, but the implementation can be bypassed due to another vulnerability. This means while the core authentication logic is correct, there is a secondary flaw that an attacker can exploit to bypass authentication entirely.

• Exploitation Methods:

• Attackers can exploit this vulnerability by identifying and leveraging the secondary weakness that bypasses authentication.
• Common techniques include exploiting incorrect access controls, leveraging flawed session management, or utilizing improper input validation to bypass intended authentication barriers.

• Security Impact:

• Direct consequences of successful exploitation include unauthorized access to systems, data, and functionalities.
• Potential cascading effects involve further exploitation of system resources, data breaches, and privilege escalation.
• Business impact can be severe, including loss of customer trust, potential legal liabilities, and financial losses due to data breaches.

• Prevention Guidelines:

• Specific code-level fixes include thoroughly auditing the code for secondary weaknesses that could affect authentication mechanisms.
• Security best practices involve implementing comprehensive threat modeling and secure design principles to ensure all components supporting authentication are secure.
• Recommended tools and frameworks include using automated security scanners and static code analysis tools to detect potential weaknesses, and adopting robust authentication libraries and frameworks that are thoroughly vetted and maintained.

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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:

# flask_app.py {15-17}
from flask import Flask, request, jsonify

app = Flask(__name__)

# Dummy user database
users = {
    "admin": {"password": "admin123", "role": "admin"},
    "user1": {"password": "user123", "role": "user"}
}

@app.route('/login', methods=['POST'])
def login():
    username = request.form.get('username')
    password = request.form.get('password')

    # Vulnerable code: Authentication bypass due to lack of password verification
    # This only checks if the username exists, not if the password matches.
    if username in users:
        return jsonify(message="Logged in as {}".format(username))
    return jsonify(message="Invalid credentials"), 401

if __name__ == '__main__':
    app.run()

Explanation of Vulnerability

• The code above checks if the username exists in the users' dictionary but does not verify if the provided password matches the stored password.
• This allows an attacker to log in as any user without knowing their password, as the password field is ignored.

How to fix Authentication Bypass by Primary Weakness?

To fix this vulnerability, ensure that both the username and password are validated. This involves:

• Verifying that the username exists in the database.
• Checking that the password provided matches the stored password for that user.
• Use secure password handling practices like hashing passwords instead of storing them in plain text.

Fixed Code Example

# flask_app.py {15-23}
from flask import Flask, request, jsonify
from werkzeug.security import check_password_hash, generate_password_hash

app = Flask(__name__)

# Dummy user database with hashed passwords
users = {
    "admin": {"password": generate_password_hash("admin123"), "role": "admin"},
    "user1": {"password": generate_password_hash("user123"), "role": "user"}
}

@app.route('/login', methods=['POST'])
def login():
    username = request.form.get('username')
    password = request.form.get('password')

    # Fixed code: Proper authentication check using password verification
    # This checks both the existence of the username and the correctness of the password.
    if username in users and check_password_hash(users[username]['password'], password):
        return jsonify(message="Logged in as {}".format(username))
    return jsonify(message="Invalid credentials"), 401

if __name__ == '__main__':
    app.run()

Explanation of Fix

• The generate_password_hash function is used to store passwords securely by hashing them.
• The check_password_hash function is used to verify the input password against the hashed password stored in the database.
• This ensures that even if someone knows the username, they cannot authenticate without the correct password, thereby preventing authentication bypass.