CWE-940: Improper Verification of Source of a Communication Channel

What is Improper Verification of Source of a Communication Channel?

• Overview: Improper Verification of Source of a Communication Channel occurs when a system establishes a communication channel in response to a request without adequately verifying the origin of that request, allowing unauthorized actors to potentially gain access or privileges.

• Exploitation Methods:

• Attackers can exploit this vulnerability by spoofing the source of a communication request, making it appear legitimate.
• Common attack patterns include man-in-the-middle attacks, IP spoofing, and domain impersonation.

• Security Impact:

• Direct consequences of successful exploitation include unauthorized access to sensitive data or system functionality.
• Potential cascading effects may include privilege escalation, data breaches, or system compromise.
• Business impact can involve financial loss, reputational damage, and regulatory penalties.

• Prevention Guidelines:

• Specific code-level fixes include implementing strict origin checks and validating the source of incoming requests.
• Security best practices involve using secure communication protocols like TLS/SSL and maintaining up-to-date access control lists.
• Recommended tools and frameworks include firewalls, intrusion detection systems, and secure API gateways to monitor and control communication requests.

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Technical Details

Likelihood of Exploit: Not specified

Affected Languages: Not Language-Specific

Affected Technologies: Mobile

Vulnerable Code Example

import requests

def fetch_data(endpoint):
    # This function does not verify the source of the incoming data
    response = requests.get(endpoint)  # Fetch data from the endpoint
    if response.status_code == 200:
        return response.json()  # Return JSON data if the request was successful
    return None  # Return None if the request failed

# Example usage
data = fetch_data('http://example.com/data')

Explanation

In this example, the fetch_data function retrieves data from a specified endpoint without verifying the source. This lack of verification can lead to serious security issues where an attacker could redirect the request to a malicious server, potentially resulting in data leaks or data manipulation.

How to fix Improper Verification of Source of a Communication Channel?

To address this vulnerability, it is crucial to implement the following security measures:

• Whitelisting: Only allow requests to approved and trusted domains.
• HTTPS: Ensure the use of secure communication channels to prevent man-in-the-middle attacks.
• Certificate Verification: Verify the server's SSL/TLS certificate to ensure it's from a trusted authority.

Fixed Code Example

import requests
from urllib.parse import urlparse

def fetch_data(endpoint):
    # Whitelist of allowed domains
    allowed_domains = ['example.com']

    # Parse the URL to extract the domain
    parsed_url = urlparse(endpoint)
    domain = parsed_url.netloc

    # Validate that the endpoint is from an allowed domain and uses HTTPS
    if domain in allowed_domains and parsed_url.scheme == 'https':
        try:
            response = requests.get(endpoint, verify=True)  # Verify SSL certificate
            if response.status_code == 200:
                return response.json()  # Return JSON data if the request was successful
        except requests.exceptions.SSLError as e:
            print(f"SSL error: {e}")  # Log SSL errors for debugging

    # Return None if the endpoint is not from a trusted source or verification fails
    return None

# Example usage
data = fetch_data('https://example.com/data')

Explanation

1. Domain Whitelisting: The code checks if the domain of the endpoint is in a predefined list of trusted domains.
2. HTTPS Enforcement: The code ensures that the endpoint uses https:// to secure the communication channel, preventing eavesdropping and man-in-the-middle attacks.
3. Certificate Verification: By setting verify=True, the code ensures that the server's SSL certificate is verified, adding an additional layer of security.

By implementing these checks, the application ensures it only communicates with trusted sources, thereby mitigating the risk associated with improper verification of the source of a communication channel.