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Lack of data validation - Non Sanitized Variables

Need​

Implementation of proper data validation and sanitization techniques

Context​

  • Usage of Python 3 for developing Python applications
  • Usage of the os module for interacting with the operating system in Node.js
  • Usage of django.http for handling HTTP requests and responses in Django

Description​

Non compliant code​

import os
from django.http import HttpResponse

def run_command(request):
    command = request.GET.get('command', '')
    os.system(command)
    return HttpResponse("Command executed successfully")

In the above code snippet, the function run_command(request) is designed to receive a GET request, extract a command from the request parameters, and execute it on the server using the os.system() function.

This is a serious security vulnerability, as it lacks proper data validation and sanitization. The application is using user-provided data (the 'command' variable) directly in a system command without first sanitizing it. This means that an attacker could potentially manipulate the 'command' variable to execute arbitrary system commands on the server.

For instance, an attacker could send a GET request with a 'command' parameter like ; rm -rf /, which would delete all files on the server if it has sufficient permissions. This is a classic example of a Command Injection vulnerability.

Steps​

  • First, avoid using user input directly in system commands. This is a bad practice as it opens up the system to command injection attacks.
  • If it's necessary to use user input in system commands, sanitize the input before using it. This can be done by removing or escaping special characters that could modify the system command.
  • Use a whitelist of allowed commands. This way, even if an attacker manages to inject a command, it won't be executed unless it's in the whitelist.
  • Consider using built-in functions or libraries that can perform the desired operation without the need for system commands. These are usually safer as they don't expose the system to command injection attacks.
  • Implement error handling to catch and handle any exceptions that may occur during the execution of the system command.

Compliant code​

import os
import shlex
from django.http import HttpResponse

ALLOWED_COMMANDS = ['ls', 'pwd', 'date']

def sanitize_command(command):
    return ''.join(ch for ch in command if ch.isalnum())

def run_command(request):
    command = request.GET.get('command', '')
    command = sanitize_command(command)
    if command in ALLOWED_COMMANDS:
        os.system(shlex.quote(command))
        return HttpResponse("Command executed successfully")
    else:
        return HttpResponse("Invalid command")

The updated code includes a function sanitize_command that sanitizes the user input by removing any character that is not alphanumeric. This effectively neutralizes special elements that could modify the system command.

The run_command function now uses the sanitized command instead of the raw user input. It also checks if the command is in the ALLOWED_COMMANDS list before executing it. This is a whitelist of allowed commands. If the command is not in the list, the function returns an "Invalid command" response.

The os.system call now uses shlex.quote to further ensure that the command is properly escaped before it's executed. This provides an additional layer of protection against command injection attacks.

This approach significantly reduces the risk of command injection attacks by ensuring that only safe, whitelisted commands can be executed and that any user input used in these commands is properly sanitized and escaped.

References​

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