CWE-637: Unnecessary Complexity in Protection Mechanism (Not Using 'Economy of Mechanism')

What is Unnecessary Complexity in Protection Mechanism (Not Using 'Economy of Mechanism')?

• Overview: This vulnerability occurs when a security mechanism is needlessly complex, making it harder to understand, implement, and maintain, potentially leading to security weaknesses.

• Exploitation Methods:

• Attackers can exploit this by taking advantage of misunderstandings or misconfigurations within the complex mechanism.
• Common attack patterns include exploiting implementation errors or compatibility issues that arise from the unnecessary complexity.

• Security Impact:

• Direct consequences include potential unauthorized access or data breaches due to misconfigured security measures.
• Potential cascading effects involve other parts of the system being compromised as attackers leverage the flawed mechanism.
• Business impact can include financial loss, damage to reputation, and legal repercussions due to data breaches or compliance failures.

• Prevention Guidelines:

• Specific code-level fixes include simplifying the security mechanism to make it easier to understand and implement correctly.
• Security best practices involve adhering to the principle of 'economy of mechanism,' ensuring that security measures are as simple and straightforward as possible.
• Recommended tools and frameworks include those that emphasize simplicity and have strong support for security, such as well-documented libraries with clear configuration guidelines.

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Technical Details

Likelihood of Exploit: Not specified

Affected Languages: Not Language-Specific

Affected Technologies: Not specified

Vulnerable Code Example

# auth_system.py {6-16}
import hashlib

class AuthSystem:
    def __init__(self):
        self.users = {}

    # Complex password hashing mechanism
    def hash_password(self, password):
        # Unnecessarily complex hashing with multiple steps
        # This complexity doesn't add real security value and is hard to maintain
        step1 = hashlib.md5(password.encode()).hexdigest()
        step2 = hashlib.sha1(step1.encode()).hexdigest()
        step3 = hashlib.sha256(step2.encode()).digest()
        step4 = hashlib.sha512(step3).hexdigest()
        return step4

    def register_user(self, username, password):
        self.users[username] = self.hash_password(password)

    def verify_user(self, username, password):
        hashed = self.hash_password(password)
        if username in self.users:
            return self.users[username] == hashed
        return False

Explanation of Vulnerability

The above code demonstrates an unnecessarily complex password hashing mechanism. The hash_password function uses multiple hashing algorithms in sequence (MD5, SHA1, SHA256, SHA512) to hash passwords. This complexity does not significantly improve security and makes the code harder to understand and maintain. Each additional step introduces potential for errors and misunderstandings. Additionally, MD5 and SHA1 are considered weak for cryptographic purposes, further undermining security.

How to fix Unnecessary Complexity in Protection Mechanism (Not Using 'Economy of Mechanism')?

To fix this vulnerability, we should simplify the password hashing mechanism by using a single, strong, and well-tested hashing algorithm that is designed for password hashing, such as bcrypt. Bcrypt is specifically designed to be slow and computationally expensive, making it more resistant to brute-force attacks. Furthermore, it automatically handles salting and key stretching, which are essential for secure password storage.

Fixed Code Example

# auth_system.py {6-13}
from passlib.hash import bcrypt

class AuthSystem:
    def __init__(self):
        self.users = {}

    # Simplified password hashing using bcrypt
    def hash_password(self, password):
        # Bcrypt handles salting and key stretching internally
        return bcrypt.hash(password)

    def register_user(self, username, password):
        self.users[username] = self.hash_password(password)

    def verify_user(self, username, password):
        if username in self.users:
            # Bcrypt's verify method checks if the password matches the hash
            return bcrypt.verify(password, self.users[username])
        return False

Explanation of Fix

The fixed code replaces the complex hashing mechanism with bcrypt, which is a well-regarded library for password hashing. This simplifies the code and enhances security by using a single, robust mechanism. Bcrypt automatically handles crucial security features such as salting and iterative hashing, which were previously managed manually (and incorrectly) in the vulnerable code. This approach not only reduces the complexity but also makes the system more secure and easier to maintain. By using bcrypt, we ensure that the password storage follows best practices, making it resistant to common attacks like brute force and rainbow table attacks.