Security Design Flaws in Password Policy and Reset Process

Introduction

While registering for a new account on a new website (not to be publicly named) I found some really interesting security design flaws. These include weak initial password requirements, the ability to downgrade an account’s security via the password reset process, and the system's tendency to reveal valid usernames during login. This article will explore these issues in depth and offer recommendations for addressing the vulnerabilities.

The Flaw: Weak Password Policy, Reset Process, and Username Enumeration

The website's password management process suffers from several significant weaknesses.

Weak Initial Password Requirements: The password policy for new or manually changed passwords is limited to fewer than 15 characters and only allows uppercase letters, lowercase letters, and numbers. This limited character set and the relatively short maximum length severely restrict password strength.

• CWE-521: Weak Password Requirements: This flaw aligns with CWE-521, where insufficient password complexity is enforced. Limiting users to fewer than 16 characters and excluding special characters significantly reduces password entropy, making the system more vulnerable to brute force and dictionary attacks.

Password Reset Can Downgrade Account Security: Any user can request a password reset for any account. When the reset occurs, the system assigns a weak, 6-character password composed of uppercase letters, lowercase letters, and numbers. This password is considerably weaker than what a user might have originally set, effectively downgrading the account’s security.

• CWE-640: Weak Password Recovery Mechanism: By allowing an attacker to initiate the reset process and forcing the account to adopt a weak password, the system creates an exploit where attackers can target specific accounts and reduce their security, making them easier to compromise.

Username Enumeration During Login: The system reveals whether a username is valid during the login process. If an invalid username is entered, the system returns an error stating that the username was not found. When a valid username is used but with the wrong password, the system provides a different error message. This discrepancy allows attackers to confirm which usernames are valid.

• CWE-203: Observable Discrepancy: This flaw relates to CWE-203, where attackers can observe system behavior (error messages) to discern information that should not be revealed—in this case, valid usernames.

Implications of the Flaw

These flaws carry severe implications for the security of user accounts and the system as a whole:

1. Reduced Password Strength from the Start: Passwords with fewer than 16 characters and without special characters are inherently weak. They are more susceptible to cracking via brute force or dictionary attacks, as the number of possible combinations is far lower than would be with a more robust policy.

• Passwords restricted to just uppercase, lowercase, and numbers fail to provide sufficient entropy, a problem that CWE-521 addresses. An attacker could quickly generate guesses or crack such passwords using modern tools, especially if the system doesn't implement account lockout or rate-limiting mechanisms.

2. Account Downgrade Exploit: The ability to request a password reset for any user allows attackers to effectively downgrade the security of the account by replacing a strong password with a much weaker one. Once a password reset has been made, a pre-generated password (with only six characters) is emailed to the email address. This attack vector is particularly dangerous if targeted at high-value accounts, such as administrators or users with elevated privileges.

• After initiating a password reset, the system overwrites the existing password with a 6-character password, which has only about 56 billion possible combinations (62^6). Given modern computing power, this password can be easily brute-forced, making the CWE-640 vulnerability highly exploitable.

3. Username Enumeration: By revealing whether a username is valid, the system enables attackers to focus their efforts on known accounts. Once a valid username is discovered, the attacker can launch brute force, dictionary, or password reset-based attacks.

• This CWE-203 vulnerability facilitates the gathering of valid usernames, significantly increasing the chances of a successful attack. Additionally, attackers could use the valid usernames to craft targeted phishing or social engineering campaigns.

Potential Exploits

Attackers could exploit these flaws in several ways:

1. Password Cracking: Due to the weak initial password requirements, attackers could use brute force or dictionary attacks to crack user passwords. Limiting passwords to less than 16 characters and excluding special characters makes them much easier to guess, especially if other protections like account lockout or rate limiting are not in place.
2. Password Reset Exploit: An attacker could request a password reset for any valid account, thereby downgrading the account’s password to a much weaker 6-character password. After this, brute force tools could quickly crack the new, weak password and gain unauthorized access.
3. Username Enumeration: By testing different usernames during login, attackers could build a list of valid accounts. Once valid usernames are known, attackers could focus on brute forcing passwords or using the reset mechanism to downgrade their security.
4. Phishing and Social Engineering: Attackers could use the valid usernames to craft convincing phishing emails or messages, tricking users into divulging their credentials or other sensitive information.

Mitigation and Recommendations

To address these vulnerabilities, the following steps are recommended:

Strengthen Password Requirements:

• The system should enforce stronger password policies, allowing for at least 16 characters and requiring a mix of upper and lowercase letters, numbers, and special characters.
• Implement regular password audits to ensure users are following best practices, addressing CWE-521 by enforcing secure and complex passwords.

Improve the Password Reset Mechanism:

• Instead of assigning a weak 6-character password, the system should prompt users to set a secure password upon reset, following the same strong password policy.
• Implement rate limiting, CAPTCHA, or other controls to prevent abuse of the reset mechanism.

3. Implement Multi-Factor Authentication (MFA):

• MFA should be required for high-value accounts and offered as an option for all users. This would ensure that even if a password is compromised, an additional authentication factor is needed to gain access.
• MFA addresses CWE-640 by adding a critical layer of security beyond just the weak password.

4. Prevent Username Enumeration:

• The system should provide generic error messages during login, such as "Invalid username or password," regardless of which credential is incorrect. This will prevent attackers from determining whether a username is valid, addressing CWE-203. It is possible that this is just a hardcoded response.

5. Rate Limiting and Account Lockouts:

• To mitigate brute force attempts, implement rate limiting and temporary account lockouts after a certain number of failed login attempts. This would make it harder for attackers to use automated tools to guess passwords.

6. Logging and Monitoring:

• Enable logging for all password reset and login attempts, and monitor for unusual activity. Alerts should be set for abnormal patterns, such as a high number of reset requests for a particular account, which could indicate an attack.

Conclusion

Weak password policies, combined with an exploitable reset mechanism and username enumeration, create significant security vulnerabilities that could be easily exploited by attackers. By enforcing stronger password requirements, improving the reset process, implementing multi-factor authentication, and preventing username enumeration, these risks can be significantly reduced. Addressing these flaws will greatly enhance the overall security posture of the system and protect user accounts from unauthorized access.