CWE-75: Failure to Sanitize Special Elements into a Different Plane (Special Element Injection)

What is Failure to Sanitize Special Elements into a Different Plane (Special Element Injection)?

• Overview: This vulnerability occurs when a software application does not properly filter or sanitize user input containing special elements, which can control the behavior of the application. Special elements can include characters or strings that have specific implications or commands within the application or its environment.

• Exploitation Methods:

• Attackers can exploit this vulnerability by injecting special elements into input fields to manipulate the application's behavior or gain unauthorized access.
• Common attack patterns include SQL injection, command injection, and XML injection, where malicious inputs are crafted to execute unintended commands or queries.

• Security Impact:

• Direct consequences of successful exploitation include unauthorized data access, data modification, or system compromise.
• Potential cascading effects can lead to broader security breaches, such as access to internal networks or further exploitations by chaining vulnerabilities.
• Business impact includes potential data breaches, loss of customer trust, legal liabilities, and financial loss due to compromised systems.

• Prevention Guidelines:

• Specific code-level fixes involve validating and escaping user inputs to ensure they are free from control characters or commands.
• Security best practices include implementing input validation, utilizing parameterized queries, and applying principle of least privilege.
• Recommended tools and frameworks include using libraries for input validation and sanitization, such as OWASP ESAPI, or leveraging language-specific security features.

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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

from flask import Flask, request

app = Flask(__name__)

@app.route('/search')
def search():
    # Vulnerable to special element injection
    query = request.args.get('query')
    # Directly using user input in HTML response without sanitization
    return f"<h1>Search Results for: {query}</h1>"

if __name__ == '__main__':
    app.run()

Explanation

• The code directly inserts user-controlled input (query) into the HTML response. This can lead to Cross-Site Scripting (XSS) attacks if special elements (e.g., <script>) are not sanitized or encoded. An attacker could inject malicious scripts that execute in the context of the user's browser.

How to fix Failure to Sanitize Special Elements into a Different Plane (Special Element Injection)?

To fix this vulnerability, we need to ensure that any user-controlled input is properly sanitized or encoded before being included in an HTML response. This can be achieved by using libraries or frameworks that automatically handle HTML escaping, or by manually escaping special characters in the input.

In the context of a Flask application, using the markupsafe library, which is automatically integrated with Flask's template rendering, helps by escaping special HTML characters. It ensures that special elements like <script> tags do not execute.

Fixed Code Example

from flask import Flask, request
from markupsafe import escape

app = Flask(__name__)

@app.route('/search')
def search():
    # Using escape to sanitize the user input
    query = request.args.get('query', type=str)
    sanitized_query = escape(query)  # Properly escape user input
    return f"<h1>Search Results for: {sanitized_query}</h1>"

if __name__ == '__main__':
    app.run()

Explanation

• The escape() function from the markupsafe library is used to automatically convert special HTML characters to their safe representations (e.g., < becomes <), preventing potential XSS attacks.
• By sanitizing the query input, we ensure that any special elements are treated as text and not executed as code. This protects the application from malicious scripts being injected and executed in the user's browser.