CWE-640: Weak Password Recovery Mechanism for Forgotten Password

What is Weak Password Recovery Mechanism for Forgotten Password?

• Overview: The CWE-640 vulnerability refers to a weak password recovery mechanism where users can reset forgotten passwords without needing the original password. This weakness makes it easier for unauthorized users to gain access to accounts, undermining the overall security of password protection.

• Exploitation Methods:

• Attackers can guess or find answers to weak security questions, especially if answers are available through social media.
• Exploitation through implementation flaws, such as tricking the system into sending password reset links to unauthorized email addresses.
• Denial of service attacks by repeatedly triggering password resets, preventing legitimate users from accessing their accounts.
• Systems sending the original password instead of a temporary one can be intercepted by attackers.

• Security Impact:

• Unauthorized access to user accounts by attackers.
• Possible data breaches and exposure of sensitive user information.
• Loss of user trust and potential damage to the business's reputation.
• Financial losses due to fraud or data protection violations.

• Prevention Guidelines:

• Implement strong, hard-to-guess security questions or use multi-factor authentication for password recovery.
• Ensure password reset links are time-limited and sent to verified email addresses only.
• Use rate limiting to prevent automated attacks and denial of service.
• Always generate a new temporary password or a reset link instead of sending the original password.
• Regularly audit and test the password recovery mechanism for vulnerabilities.

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Technical Details

Likelihood of Exploit: High

Affected Languages: Not Language-Specific

Affected Technologies: Not specified

Vulnerable Code Example

Python Example

The following Python code demonstrates a weak password recovery mechanism. The vulnerability lies in using a predictable token for password reset, which could be easily guessed by an attacker.

import random
import string

def generate_reset_token(email):
    # Vulnerable: Using a predictable token generation method
    # The token is composed of a fixed string and a predictable random number
    fixed_part = "RESET"
    random_part = str(random.randint(1000, 9999))  # Predictable four-digit number
    token = fixed_part + random_part
    return token

def request_password_reset(email):
    token = generate_reset_token(email)
    # Send email to user with reset token
    print(f"Password reset token for {email}: {token}")

# Example usage
request_password_reset("user@example.com")

Vulnerability Explanation

• Predictability: The token is generated using a fixed string and a predictable four-digit number, making it susceptible to guessing attacks.
• Lack of Expiration: There is no mechanism to associate the token with a user or to set an expiration time, allowing indefinite reuse of the token if intercepted.

How to fix Weak Password Recovery Mechanism for Forgotten Password?

Fixed Code Example

The fixed version uses Python's secrets module to generate a secure token.

import secrets
import string

def generate_secure_reset_token(email):
    # Fix: Using a cryptographically secure random number generator
    # Generate a random token with a combination of letters and digits
    token = ''.join(secrets.choice(string.ascii_letters + string.digits) for _ in range(20))
    return token

def request_password_reset(email):
    token = generate_secure_reset_token(email)
    # Securely associate the token with the user's email and set an expiration time
    # Send email to user with secure reset token
    print(f"Password reset token for {email}: {token}")

# Example usage
request_password_reset("user@example.com")

Fix Explanation

• Cryptographic Security: The secrets module is used to generate a token with a high degree of randomness, making it resistant to guessing attacks.
• Token Complexity: The token is composed of a mix of letters and digits, with a length of 20 characters, enhancing security.
• Best Practices: Although not shown in the code, it is essential to associate the token with a specific user and implement an expiration mechanism to ensure tokens cannot be reused indefinitely.