Patched code sample

import ast
from flask import Flask, request, jsonify

# This example uses the Flask web framework to simulate the API endpoint.
# The provided CVE-2026-0768 is fictional. This code addresses the principles
# of the real vulnerability it describes (likely CVE-2024-2734 in Langflow),
# where user-supplied code was unsafely executed via exec() or eval().

app = Flask(__name__)

@app.route("/validate", methods=["POST"])
def fixed_validate_endpoint():
    """
    A secure endpoint to validate Python code syntax.
    This function represents the fix for the described vulnerability.
    It replaces dangerous code execution with safe syntax tree parsing.
    """
    try:
        data = request.get_json()
        if not data or "code" not in data:
            return jsonify({"valid": False, "error": "Request body must be JSON and contain a 'code' field."}), 400

        code_to_validate = data["code"]

        if not isinstance(code_to_validate, str):
             return jsonify({"valid": False, "error": "'code' field must be a string."}), 400

        # THE FIX:
        # Instead of using a dangerous function like exec() or eval() on user
        # input, we safely parse the code into an Abstract Syntax Tree (AST).
        # The ast.parse() function checks for valid Python syntax without
        # ever executing the code. If the code is syntactically incorrect,
        # it will raise a SyntaxError, which is caught below.
        ast.parse(code_to_validate)

        # If ast.parse() completes without an exception, the code is syntactically valid.
        return jsonify({"valid": True, "error": None}), 200

    except SyntaxError as e:
        # This is the expected and safe outcome for syntactically invalid Python code.
        return jsonify({"valid": False, "error": f"Syntax Error: {e}"}), 400
    except Exception as e:
        # Catch any other unexpected errors during processing.
        return jsonify({"valid": False, "error": f"An unexpected error occurred: {str(e)}"}), 500

if __name__ == '__main__':
    # To run this demonstration:
    # 1. pip install Flask
    # 2. python <filename>.py
    # 3. Use a tool like curl to test the endpoint.

    # Example of a safe, valid request:
    # curl -X POST -H "Content-Type: application/json" -d '{"code": "import os\n\ndef my_func():\n    return True"}' http://127.0.0.1:5000/validate
    # Expected output: {"valid": true, "error": null}

    # Example of a malicious payload that is safely rejected as valid syntax:
    # curl -X POST -H "Content-Type: application/json" -d '{"code": "__import__(\"os\").system(\"echo pwned\")"}' http://127.0.0.1:5000/validate
    # Expected output: {"valid": true, "error": null} -> Note: The code is not executed, only validated.

    # Example of a syntactically invalid request that is safely rejected:
    # curl -X POST -H "Content-Type: application/json" -d '{"code": "print(hello"}' http://127.0.0.1:5000/validate
    # Expected output: {"valid": false, "error": "Syntax Error: ..."}

    app.run(port=5000)