import hashlib import logging import os from urllib.parse import urlparse from itsdangerous import BadData, SignatureExpired, URLSafeTimedSerializer from quart import current_app, g, request, session from werkzeug.exceptions import BadRequest from werkzeug.security import safe_str_cmp from wtforms import ValidationError __all__ = ('generate_csrf', 'validate_csrf', 'CSRFProtect') logger = logging.getLogger(__name__) def generate_csrf(secret_key=None, token_key=None): """Generate a CSRF token. The token is cached for a request, so multiple calls to this function will generate the same token. During testing, it might be useful to access the signed token in ``g.csrf_token`` and the raw token in ``session['csrf_token']``. :param secret_key: Used to securely sign the token. Default is ``QUART_CSRF_SECRET_KEY`` or ``SECRET_KEY``. :param token_key: Key where token is stored in session for comparison. Default is ``QUART_CSRF_FIELD_NAME`` or ``'csrf_token'``. """ secret_key = _get_config( secret_key, 'QUART_CSRF_SECRET_KEY', current_app.secret_key, message='A secret key is required to use CSRF.' ) field_name = _get_config( token_key, 'QUART_CSRF_FIELD_NAME', 'csrf_token', message='A field name is required to use CSRF.' ) if field_name not in g: s = URLSafeTimedSerializer(secret_key, salt='quart-csrf-token') if field_name not in session: session[field_name] = hashlib.sha1(os.urandom(64)).hexdigest() try: token = s.dumps(session[field_name]) except TypeError: session[field_name] = hashlib.sha1(os.urandom(64)).hexdigest() token = s.dumps(session[field_name]) setattr(g, field_name, token) return g.get(field_name) def validate_csrf(data, secret_key=None, time_limit=None, token_key=None): """Check if the given data is a valid CSRF token. This compares the given signed token to the one stored in the session. :param data: The signed CSRF token to be checked. :param secret_key: Used to securely sign the token. Default is ``QUART_CSRF_SECRET_KEY`` or ``SECRET_KEY``. :param time_limit: Number of seconds that the token is valid. Default is ``QUART_CSRF_TIME_LIMIT`` or 3600 seconds (60 minutes). :param token_key: Key where token is stored in session for comparison. Default is ``QUART_CSRF_FIELD_NAME`` or ``'csrf_token'``. :raises ValidationError: Contains the reason that validation failed. .. versionchanged:: 0.14 Raises ``ValidationError`` with a specific error message rather than returning ``True`` or ``False``. """ secret_key = _get_config( secret_key, 'QUART_CSRF_SECRET_KEY', current_app.secret_key, message='A secret key is required to use CSRF.' ) field_name = _get_config( token_key, 'QUART_CSRF_FIELD_NAME', 'csrf_token', message='A field name is required to use CSRF.' ) time_limit = _get_config( time_limit, 'QUART_CSRF_TIME_LIMIT', 3600, required=False ) if not data: raise ValidationError('The CSRF token is missing.') if field_name not in session: raise ValidationError('The CSRF session token is missing.') s = URLSafeTimedSerializer(secret_key, salt='quart-csrf-token') try: token = s.loads(data, max_age=time_limit) except SignatureExpired: raise ValidationError('The CSRF token has expired.') except BadData: raise ValidationError('The CSRF token is invalid.') if not safe_str_cmp(session[field_name], token): raise ValidationError('The CSRF tokens do not match.') def _get_config( value, config_name, default=None, required=True, message='CSRF is not configured.' ): """Find config value based on provided value, Flask config, and default value. :param value: already provided config value :param config_name: Flask ``config`` key :param default: default value if not provided or configured :param required: whether the value must not be ``None`` :param message: error message if required config is not found :raises KeyError: if required config is not found """ if value is None: value = current_app.config.get(config_name, default) if required and value is None: raise RuntimeError(message) return value class CSRFProtect: """Enable CSRF protection globally for a Flask app. :: app = Flask(__name__) csrf = CSRFProtect(app) Checks the ``csrf_token`` field sent with forms, or the ``X-CSRFToken`` header sent with JavaScript requests. Render the token in templates using ``{{ csrf_token() }}``. See the :ref:`csrf` documentation. """ def __init__(self, app=None): if app: self.init_app(app) def init_app(self, app): app.extensions['csrf'] = self app.config.setdefault('QUART_CSRF_ENABLED', True) app.config.setdefault('QUART_CSRF_CHECK_DEFAULT', True) app.config['QUART_CSRF_METHODS'] = set(app.config.get( 'QUART_CSRF_METHODS', ['POST', 'PUT', 'PATCH', 'DELETE'] )) app.config.setdefault('QUART_CSRF_FIELD_NAME', 'csrf_token') app.config.setdefault( 'QUART_CSRF_HEADERS', ['X-CSRFToken', 'X-CSRF-Token'] ) app.config.setdefault('QUART_CSRF_TIME_LIMIT', 3600) app.config.setdefault('QUART_CSRF_SSL_STRICT', True) app.jinja_env.globals['csrf_token'] = generate_csrf app.context_processor(lambda: {'csrf_token': generate_csrf}) @app.before_request async def csrf_protect(): if not app.config['QUART_CSRF_ENABLED']: return if not app.config['QUART_CSRF_CHECK_DEFAULT']: return if request.method not in app.config['QUART_CSRF_METHODS']: return if not request.endpoint: return await self.protect() async def _get_csrf_token(self): # find the token in the form data form = await request.form field_name = current_app.config['QUART_CSRF_FIELD_NAME'] base_token = form.get(field_name) if base_token: return base_token # if the form has a prefix, the name will be {prefix}-csrf_token for key in form: if key.endswith(field_name): csrf_token = form[key] if csrf_token: return csrf_token # find the token in the headers for header_name in current_app.config['QUART_CSRF_HEADERS']: csrf_token = request.headers.get(header_name) if csrf_token: return csrf_token return None async def protect(self): if request.method not in current_app.config['QUART_CSRF_METHODS']: return try: validate_csrf(await self._get_csrf_token()) except ValidationError as e: logger.info(e.args[0]) self._error_response(e.args[0]) if request.is_secure and current_app.config['QUART_CSRF_SSL_STRICT']: if not request.referrer: self._error_response('The referrer header is missing.') good_referrer = f'https://{request.host}/' if not same_origin(request.referrer, good_referrer): self._error_response('The referrer does not match the host.') g.csrf_valid = True # mark this request as CSRF valid def _error_response(self, reason): raise CSRFError(reason) class CSRFError(BadRequest): """Raise if the client sends invalid CSRF data with the request. Generates a 400 Bad Request response with the failure reason by default. Customize the response by registering a handler with :meth:`flask.Flask.errorhandler`. """ description = 'CSRF validation failed.' def same_origin(current_uri, compare_uri): current = urlparse(current_uri) compare = urlparse(compare_uri) return ( current.scheme == compare.scheme and current.hostname == compare.hostname and current.port == compare.port )