CWE-437: Incomplete Model of Endpoint Features

What is Incomplete Model of Endpoint Features?

• Overview: A vulnerability where a software product acts as a go-between or monitor for endpoints but lacks a full understanding of those endpoints' features, behaviors, or states, leading to potential misbehavior or incorrect actions.

• Exploitation Methods:

• Attackers can exploit this by sending unexpected or malformed data that the intermediary fails to handle correctly due to its incomplete model.
• Common attack patterns include manipulating data flows, injecting data that the intermediary cannot process correctly, or causing it to misinterpret endpoint states.

• Security Impact:

• Direct consequences include incorrect processing of data, unauthorized access, or data leakage.
• Potential cascading effects involve broader system failures or allowing attackers to manipulate other connected components.
• Business impact could consist of data breaches, loss of customer trust, and legal liabilities.

• Prevention Guidelines:

• Specific code-level fixes include ensuring thorough validation and understanding of endpoint features and behaviors.
• Security best practices involve keeping comprehensive documentation of endpoint capabilities and regular updates to intermediary software.
• Recommended tools and frameworks include using endpoint simulation tools to test intermediary handling and employing comprehensive logging and monitoring of endpoint interactions.

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Technical Details

Likelihood of Exploit: Not specified

Affected Languages: Not Language-Specific

Affected Technologies: Not specified

Vulnerable Code Example

import requests

class APIGateway:
    def __init__(self, endpoints):
        self.endpoints = endpoints

    def process_request(self, endpoint_name, data):
        # Vulnerable: Assuming the endpoint supports POST request without verifying
        response = requests.post(self.endpoints[endpoint_name], json=data)
        return response.json()

# Example usage
endpoints = {
    "user_service": "http://user-service/api/users",
    "order_service": "http://order-service/api/orders"
}

gateway = APIGateway(endpoints)
response = gateway.process_request("order_service", {"order_id": 123})
print(response)

Explanation:

• Vulnerability: The process_request method assumes that all endpoints support POST requests. If an endpoint only supports GET requests, this will fail or lead to unexpected behavior.
• Security Issue: The code does not have a complete model of the endpoint's capabilities (i.e., the supported HTTP methods), leading to potential miscommunication and failures.

How to fix Incomplete Model of Endpoint Features?

To fix this vulnerability, the program should maintain a complete model of each endpoint's features, including supported HTTP methods. This can be achieved by:

1. Defining Endpoint Capabilities: Maintain a dictionary of endpoints with their supported HTTP methods.
2. Validating Requests: Before making a request, verify if the desired HTTP method is supported by the endpoint.
3. Error Handling: Implement error handling to manage unsupported operations gracefully.

Fixed Code Example

import requests

class APIGateway:
    def __init__(self, endpoints):
        self.endpoints = endpoints

    def process_request(self, endpoint_name, method, data=None):
        # Fix: Check if the requested method is supported by the endpoint
        if method not in self.endpoints[endpoint_name]['methods']:
            raise ValueError(f"HTTP method {method} not supported by {endpoint_name}")

        url = self.endpoints[endpoint_name]['url']
        # Fixed: Dynamically choose the request method based on the endpoint's capabilities
        if method == 'POST':
            response = requests.post(url, json=data)
        elif method == 'GET':
            response = requests.get(url, params=data)
        else:
            raise ValueError("Unsupported HTTP method")

        return response.json()

# Example usage
endpoints = {
    "user_service": {"url": "http://user-service/api/users", "methods": ["GET", "POST"]},
    "order_service": {"url": "http://order-service/api/orders", "methods": ["GET"]}
}

gateway = APIGateway(endpoints)
try:
    response = gateway.process_request("order_service", "POST", {"order_id": 123})
except ValueError as e:
    print(e)  # Prints an error about unsupported HTTP method

Explanation:

• Endpoint Capabilities: Each endpoint now includes a list of supported HTTP methods, ensuring the code has a complete model of the endpoint's features.
• Validation and Error Handling: The process_request method validates the method before making requests and raises an error if the method is unsupported.
• Dynamic Method Selection: The code dynamically selects the correct HTTP method based on the endpoint's capabilities, preventing incorrect requests.