CWE-620: Unverified Password Change

What is Unverified Password Change?

• Overview: Unverified Password Change (CWE-620) is a vulnerability where a system allows a user to change their password without verifying their identity through the original password or another form of authentication. This can lead to unauthorized access if exploited by an attacker.

• Exploitation Methods:

• Attackers can exploit this vulnerability by gaining access to a user's account and changing the password without needing to know the original password.
• Common attack patterns include phishing attacks to gain initial access or exploiting weak authentication mechanisms that allow simple access to the password change functionality.

• Security Impact:

• Direct consequences of successful exploitation include unauthorized access to user accounts, leading to potential data theft or manipulation.
• Potential cascading effects include compromised user data, unauthorized transactions, and further system intrusions if the account has administrative privileges.
• Business impact can involve financial loss, reputational damage, and legal liabilities due to compromised customer data or breach of privacy regulations.

• Prevention Guidelines:

• Specific code-level fixes include implementing checks that require users to enter their current password or use two-factor authentication (2FA) during a password change process.
• Security best practices involve regularly auditing authentication and password management processes to ensure they adhere to security standards.
• Recommended tools and frameworks include using libraries that provide secure authentication mechanisms, such as OAuth, and incorporating strong encryption for password storage and transmission.

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Technical Details

Likelihood of Exploit: Not specified

Affected Languages: Not Language-Specific

Affected Technologies: Not specified

Vulnerable Code Example

class UserService:
    def change_password(self, username, new_password):
        # Vulnerable code: Password change without verifying the current password or identity
        user = self.get_user(username)
        user.password = new_password
        self.save_user(user)

Explanation:

• In this vulnerable example, the change_password method allows changing a user's password without verifying the user's identity or the current password. This flaw could be exploited by an attacker who gains access to the username, allowing unauthorized password changes.

How to fix Unverified Password Change?

To fix this vulnerability, always verify the user's identity before allowing a password change. This can be done by:

1. Requiring the current password to be provided along with the new password.
2. Alternatively, using another form of authentication, such as two-factor authentication (2FA), to verify the user's identity.
3. Implementing secure password hashing and comparison to prevent direct password exposure.

Fixed Code Example

import hashlib

class UserService:
    def change_password(self, username, current_password, new_password):
        # Fixed code: Verify the current password before allowing the password change
        user = self.get_user(username)
        if self.verify_password(user.password, current_password):  # Verify current password
            user.password = self.hash_password(new_password)       # Hash new password before saving
            self.save_user(user)
        else:
            raise ValueError("Current password is incorrect")

    def verify_password(self, stored_password, provided_password):
        # Securely compare hashed passwords using constant time comparison to prevent timing attacks
        return stored_password == hashlib.sha256(provided_password.encode()).hexdigest()

    def hash_password(self, password):
        # Hash password using SHA-256
        return hashlib.sha256(password.encode()).hexdigest()

Explanation:

• The fixed code requires the user to provide their current password before a password change is allowed, ensuring the request is legitimate.
• Passwords are hashed using SHA-256 before storage and comparison, enhancing security by not storing or comparing plaintext passwords.
• This approach combines password verification with secure password handling practices to mitigate the risk of unauthorized password changes.
• Additionally, ensure that password comparison is done in constant time to prevent timing attacks, though this example uses a simple equality check for demonstration. In a production environment, consider using libraries like hmac.compare_digest for secure comparisons.