CWE-307: Improper Restriction of Excessive Authentication Attempts

What is Improper Restriction of Excessive Authentication Attempts?

• Overview: CWE-307 refers to a security vulnerability where a system does not have adequate measures in place to limit the number of failed authentication attempts, allowing attackers to repeatedly attempt to guess valid credentials.

• Exploitation Methods:

• Attackers can exploit this vulnerability by employing brute force attacks, repeatedly attempting to guess passwords or other authentication credentials.
• Common attack patterns include automated scripts that try multiple password combinations quickly or using lists of common passwords to gain unauthorized access.

• Security Impact:

• Direct consequences include unauthorized access to user accounts, potentially leading to data breaches or account takeover.
• Potential cascading effects involve lateral movement within a system, where attackers use compromised credentials to access other sensitive areas.
• Business impact includes loss of user trust, potential legal repercussions, and financial losses due to unauthorized transactions or data theft.

• Prevention Guidelines:

• Specific code-level fixes include implementing account lockout mechanisms after a certain number of failed attempts, and introducing exponential backoff or CAPTCHA challenges.
• Security best practices involve monitoring and logging authentication attempts, and using multi-factor authentication (MFA) to add an additional layer of security.
• Recommended tools and frameworks include using libraries or APIs that provide built-in rate limiting and lockout features, and employing application firewalls to detect and block suspicious activities.

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Technical Details

Likelihood of Exploit: Not specified

Affected Languages: Not Language-Specific

Affected Technologies: Not specified

Vulnerable Code Example

Python Example

import time

class AuthService:
    def __init__(self):
        self.user_passwords = {"user1": "password123"}  # For demonstration purposes

    def authenticate(self, username, password):
        # No restriction on the number of authentication attempts
        if username in self.user_passwords and self.user_passwords[username] == password:
            return "Authenticated"
        return "Authentication Failed"

auth_service = AuthService()

# Simulating brute force attack
for attempt in range(5):
    result = auth_service.authenticate("user1", "wrongpassword")
    print(f"Attempt {attempt + 1}: {result}")

Explanation

• The code above demonstrates a vulnerable authentication system where there is no restriction on the number of failed authentication attempts.
• An attacker could repeatedly try different passwords without any delay or penalty, making it susceptible to brute force attacks.

How to fix Improper Restriction of Excessive Authentication Attempts?

To fix this vulnerability, implement a rate-limiting mechanism to restrict excessive authentication attempts. This can be achieved by:

1. Tracking Failed Attempts: Maintain a record of failed login attempts for each user.
2. Locking Accounts Temporarily: Temporarily lock accounts after a set number of failed attempts.
3. Imposing Delays: Introduce a delay before allowing the next attempt after a series of failures.
4. Logging and Alerting: Log excessive failed attempts and alert administrators for potential brute force attacks.

Fixed Code Example

import time

class AuthService:
    def __init__(self):
        self.user_passwords = {"user1": "password123"}
        self.failed_attempts = {}  # Track failed attempts
        self.lockout_time = 60  # 1 minute lockout period

    def authenticate(self, username, password):
        if username in self.failed_attempts:
            attempt_info = self.failed_attempts[username]
            if attempt_info['count'] >= 3:  # Lock account after 3 failed attempts
                elapsed_time = time.time() - attempt_info['last_attempt']
                if elapsed_time < self.lockout_time:
                    return "Account temporarily locked. Try again later."

        if username in self.user_passwords and self.user_passwords[username] == password:
            self.failed_attempts.pop(username, None)  # Reset failed attempts on success
            return "Authenticated"
        
        # Increment failed attempt count
        if username not in self.failed_attempts:
            self.failed_attempts[username] = {'count': 1, 'last_attempt': time.time()}
        else:
            self.failed_attempts[username]['count'] += 1
            self.failed_attempts[username]['last_attempt'] = time.time()
        return "Authentication Failed"

auth_service = AuthService()

# Simulating brute force attack
for attempt in range(5):
    result = auth_service.authenticate("user1", "wrongpassword")
    print(f"Attempt {attempt + 1}: {result}")
    time.sleep(1)  # Simulate time delay between attempts

Explanation

• Failed Attempts Tracking: The code now tracks the number of failed attempts with timestamps for each user.
• Account Locking and Delays: If a user fails to log in three times in a row, their account is temporarily locked for one minute. This prevents rapid-fire brute force attempts.
• Reset on Success: Successful authentication resets the failed attempt count, ensuring users aren't locked out after entering the correct password.