365 lines
11 KiB
Python
365 lines
11 KiB
Python
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import hashlib
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import logging
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import os
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import warnings
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from functools import wraps
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from flask import Blueprint, current_app, g, request, session
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from itsdangerous import BadData, SignatureExpired, URLSafeTimedSerializer
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from werkzeug.exceptions import BadRequest
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from werkzeug.security import safe_str_cmp
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from wtforms import ValidationError
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from wtforms.csrf.core import CSRF
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from ._compat import FlaskWTFDeprecationWarning, string_types, urlparse
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__all__ = ('generate_csrf', 'validate_csrf', 'CSRFProtect')
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logger = logging.getLogger(__name__)
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def generate_csrf(secret_key=None, token_key=None):
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"""Generate a CSRF token. The token is cached for a request, so multiple
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calls to this function will generate the same token.
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During testing, it might be useful to access the signed token in
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``g.csrf_token`` and the raw token in ``session['csrf_token']``.
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:param secret_key: Used to securely sign the token. Default is
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``WTF_CSRF_SECRET_KEY`` or ``SECRET_KEY``.
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:param token_key: Key where token is stored in session for comparision.
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Default is ``WTF_CSRF_FIELD_NAME`` or ``'csrf_token'``.
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"""
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secret_key = _get_config(
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secret_key, 'WTF_CSRF_SECRET_KEY', current_app.secret_key,
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message='A secret key is required to use CSRF.'
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)
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field_name = _get_config(
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token_key, 'WTF_CSRF_FIELD_NAME', 'csrf_token',
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message='A field name is required to use CSRF.'
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)
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if field_name not in g:
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if field_name not in session:
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session[field_name] = hashlib.sha1(os.urandom(64)).hexdigest()
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s = URLSafeTimedSerializer(secret_key, salt='wtf-csrf-token')
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setattr(g, field_name, s.dumps(session[field_name]))
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return g.get(field_name)
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def validate_csrf(data, secret_key=None, time_limit=None, token_key=None):
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"""Check if the given data is a valid CSRF token. This compares the given
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signed token to the one stored in the session.
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:param data: The signed CSRF token to be checked.
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:param secret_key: Used to securely sign the token. Default is
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``WTF_CSRF_SECRET_KEY`` or ``SECRET_KEY``.
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:param time_limit: Number of seconds that the token is valid. Default is
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``WTF_CSRF_TIME_LIMIT`` or 3600 seconds (60 minutes).
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:param token_key: Key where token is stored in session for comparision.
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Default is ``WTF_CSRF_FIELD_NAME`` or ``'csrf_token'``.
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:raises ValidationError: Contains the reason that validation failed.
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.. versionchanged:: 0.14
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Raises ``ValidationError`` with a specific error message rather than
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returning ``True`` or ``False``.
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"""
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secret_key = _get_config(
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secret_key, 'WTF_CSRF_SECRET_KEY', current_app.secret_key,
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message='A secret key is required to use CSRF.'
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)
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field_name = _get_config(
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token_key, 'WTF_CSRF_FIELD_NAME', 'csrf_token',
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message='A field name is required to use CSRF.'
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)
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time_limit = _get_config(
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time_limit, 'WTF_CSRF_TIME_LIMIT', 3600, required=False
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)
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if not data:
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raise ValidationError('The CSRF token is missing.')
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if field_name not in session:
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raise ValidationError('The CSRF session token is missing.')
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s = URLSafeTimedSerializer(secret_key, salt='wtf-csrf-token')
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try:
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token = s.loads(data, max_age=time_limit)
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except SignatureExpired:
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raise ValidationError('The CSRF token has expired.')
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except BadData:
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raise ValidationError('The CSRF token is invalid.')
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if not safe_str_cmp(session[field_name], token):
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raise ValidationError('The CSRF tokens do not match.')
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def _get_config(
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value, config_name, default=None,
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required=True, message='CSRF is not configured.'
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):
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"""Find config value based on provided value, Flask config, and default
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value.
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:param value: already provided config value
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:param config_name: Flask ``config`` key
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:param default: default value if not provided or configured
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:param required: whether the value must not be ``None``
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:param message: error message if required config is not found
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:raises KeyError: if required config is not found
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"""
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if value is None:
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value = current_app.config.get(config_name, default)
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if required and value is None:
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raise KeyError(message)
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return value
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class _FlaskFormCSRF(CSRF):
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def setup_form(self, form):
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self.meta = form.meta
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return super(_FlaskFormCSRF, self).setup_form(form)
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def generate_csrf_token(self, csrf_token_field):
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return generate_csrf(
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secret_key=self.meta.csrf_secret,
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token_key=self.meta.csrf_field_name
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)
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def validate_csrf_token(self, form, field):
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if g.get('csrf_valid', False):
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# already validated by CSRFProtect
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return
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try:
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validate_csrf(
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field.data,
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self.meta.csrf_secret,
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self.meta.csrf_time_limit,
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self.meta.csrf_field_name
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)
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except ValidationError as e:
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logger.info(e.args[0])
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raise
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class CSRFProtect(object):
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"""Enable CSRF protection globally for a Flask app.
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::
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app = Flask(__name__)
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csrf = CsrfProtect(app)
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Checks the ``csrf_token`` field sent with forms, or the ``X-CSRFToken``
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header sent with JavaScript requests. Render the token in templates using
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``{{ csrf_token() }}``.
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See the :ref:`csrf` documentation.
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"""
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def __init__(self, app=None):
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self._exempt_views = set()
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self._exempt_blueprints = set()
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if app:
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self.init_app(app)
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def init_app(self, app):
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app.extensions['csrf'] = self
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app.config.setdefault('WTF_CSRF_ENABLED', True)
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app.config.setdefault('WTF_CSRF_CHECK_DEFAULT', True)
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app.config['WTF_CSRF_METHODS'] = set(app.config.get(
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'WTF_CSRF_METHODS', ['POST', 'PUT', 'PATCH', 'DELETE']
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))
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app.config.setdefault('WTF_CSRF_FIELD_NAME', 'csrf_token')
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app.config.setdefault(
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'WTF_CSRF_HEADERS', ['X-CSRFToken', 'X-CSRF-Token']
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)
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app.config.setdefault('WTF_CSRF_TIME_LIMIT', 3600)
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app.config.setdefault('WTF_CSRF_SSL_STRICT', True)
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app.jinja_env.globals['csrf_token'] = generate_csrf
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app.context_processor(lambda: {'csrf_token': generate_csrf})
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@app.before_request
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def csrf_protect():
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if not app.config['WTF_CSRF_ENABLED']:
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return
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if not app.config['WTF_CSRF_CHECK_DEFAULT']:
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return
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if request.method not in app.config['WTF_CSRF_METHODS']:
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return
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if not request.endpoint:
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return
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view = app.view_functions.get(request.endpoint)
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if not view:
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return
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if request.blueprint in self._exempt_blueprints:
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return
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dest = '%s.%s' % (view.__module__, view.__name__)
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if dest in self._exempt_views:
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return
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self.protect()
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def _get_csrf_token(self):
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# find the ``csrf_token`` field in the subitted form
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# if the form had a prefix, the name will be
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# ``{prefix}-csrf_token``
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field_name = current_app.config['WTF_CSRF_FIELD_NAME']
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for key in request.form:
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if key.endswith(field_name):
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csrf_token = request.form[key]
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if csrf_token:
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return csrf_token
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for header_name in current_app.config['WTF_CSRF_HEADERS']:
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csrf_token = request.headers.get(header_name)
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if csrf_token:
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return csrf_token
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return None
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def protect(self):
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if request.method not in current_app.config['WTF_CSRF_METHODS']:
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return
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try:
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validate_csrf(self._get_csrf_token())
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except ValidationError as e:
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logger.info(e.args[0])
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self._error_response(e.args[0])
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if request.is_secure and current_app.config['WTF_CSRF_SSL_STRICT']:
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if not request.referrer:
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self._error_response('The referrer header is missing.')
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good_referrer = 'https://{0}/'.format(request.host)
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if not same_origin(request.referrer, good_referrer):
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self._error_response('The referrer does not match the host.')
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g.csrf_valid = True # mark this request as CSRF valid
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def exempt(self, view):
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"""Mark a view or blueprint to be excluded from CSRF protection.
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::
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@app.route('/some-view', methods=['POST'])
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@csrf.exempt
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def some_view():
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...
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::
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bp = Blueprint(...)
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csrf.exempt(bp)
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"""
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if isinstance(view, Blueprint):
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self._exempt_blueprints.add(view.name)
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return view
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if isinstance(view, string_types):
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view_location = view
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else:
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view_location = '%s.%s' % (view.__module__, view.__name__)
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self._exempt_views.add(view_location)
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return view
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def _error_response(self, reason):
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raise CSRFError(reason)
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def error_handler(self, view):
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"""Register a function that will generate the response for CSRF errors.
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.. deprecated:: 0.14
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Use the standard Flask error system with
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``@app.errorhandler(CSRFError)`` instead. This will be removed in
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version 1.0.
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The function will be passed one argument, ``reason``. By default it will
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raise a :class:`~flask_wtf.csrf.CSRFError`. ::
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@csrf.error_handler
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def csrf_error(reason):
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return render_template('error.html', reason=reason)
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Due to historical reasons, the function may either return a response
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or raise an exception with :func:`flask.abort`.
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"""
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warnings.warn(FlaskWTFDeprecationWarning(
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'"@csrf.error_handler" is deprecated. Use the standard Flask error '
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'system with "@app.errorhandler(CSRFError)" instead. This will be'
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'removed in 1.0.'
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), stacklevel=2)
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@wraps(view)
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def handler(reason):
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response = current_app.make_response(view(reason))
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raise CSRFError(response.get_data(as_text=True), response=response)
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self._error_response = handler
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return view
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class CsrfProtect(CSRFProtect):
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"""
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.. deprecated:: 0.14
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Renamed to :class:`~flask_wtf.csrf.CSRFProtect`.
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"""
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def __init__(self, app=None):
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warnings.warn(FlaskWTFDeprecationWarning(
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'"flask_wtf.CsrfProtect" has been renamed to "CSRFProtect" '
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'and will be removed in 1.0.'
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), stacklevel=2)
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super(CsrfProtect, self).__init__(app=app)
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class CSRFError(BadRequest):
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"""Raise if the client sends invalid CSRF data with the request.
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Generates a 400 Bad Request response with the failure reason by default.
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Customize the response by registering a handler with
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:meth:`flask.Flask.errorhandler`.
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"""
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description = 'CSRF validation failed.'
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def same_origin(current_uri, compare_uri):
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current = urlparse(current_uri)
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compare = urlparse(compare_uri)
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return (
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current.scheme == compare.scheme
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and current.hostname == compare.hostname
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and current.port == compare.port
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)
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